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Find video protocols related to scientific articles indexed in Pubmed.
Rapid diversification of five Oryza AA genomes associated with rice adaptation.
Proc. Natl. Acad. Sci. U.S.A.
PUBLISHED: 11-03-2014
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Comparative genomic analyses among closely related species can greatly enhance our understanding of plant gene and genome evolution. We report de novo-assembled AA-genome sequences for Oryza nivara, Oryza glaberrima, Oryza barthii, Oryza glumaepatula, and Oryza meridionalis. Our analyses reveal massive levels of genomic structural variation, including segmental duplication and rapid gene family turnover, with particularly high instability in defense-related genes. We show, on a genomic scale, how lineage-specific expansion or contraction of gene families has led to their morphological and reproductive diversification, thus enlightening the evolutionary process of speciation and adaptation. Despite strong purifying selective pressures on most Oryza genes, we documented a large number of positively selected genes, especially those genes involved in flower development, reproduction, and resistance-related processes. These diversifying genes are expected to have played key roles in adaptations to their ecological niches in Asia, South America, Africa and Australia. Extensive variation in noncoding RNA gene numbers, function enrichment, and rates of sequence divergence might also help account for the different genetic adaptations of these rice species. Collectively, these resources provide new opportunities for evolutionary genomics, numerous insights into recent speciation, a valuable database of functional variation for crop improvement, and tools for efficient conservation of wild rice germplasm.
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Natural insertions in rice commonly form tandem duplications indicative of patch-mediated double-strand break induction and repair.
Proc. Natl. Acad. Sci. U.S.A.
PUBLISHED: 04-23-2014
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The insertion of DNA into a genome can result in the duplication and dispersal of functional sequences through the genome. In addition, a deeper understanding of insertion mechanisms will inform methods of genetic engineering and plant transformation. Exploiting structural variations in numerous rice accessions, we have inferred and analyzed intermediate length (10-1,000 bp) insertions in plants. Insertions in this size class were found to be approximately equal in frequency to deletions, and compound insertion-deletions comprised only 0.1% of all events. Our findings indicate that, as observed in humans, tandem or partially tandem duplications are the dominant form of insertion (48%), although short duplications from ectopic donors account for a sizable fraction of insertions in rice (38%). Many nontandem duplications contain insertions from nearby DNA (within 200 bp) and can contain multiple donor sources--some distant--in single events. Although replication slippage is a plausible explanation for tandem duplications, the end homology required in such a model is most often absent and rarely is >5 bp. However, end homology is commonly longer than expected by chance. Such findings lead us to favor a model of patch-mediated double-strand-break creation followed by nonhomologous end-joining. Additionally, a striking bias toward 31-bp partially tandem duplications suggests that errors in nucleotide excision repair may be resolved via a similar, but distinct, pathway. In summary, the analysis of recent insertions in rice suggests multiple underappreciated causes of structural variation in eukaryotes.
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Variation in allelic expression associated with a recombination hotspot in Zea mays.
Plant J.
PUBLISHED: 03-28-2014
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Gene expression is a complex process, requiring precise spatial and temporal regulation of transcription factor activity; however, modifications of individual cis- and trans-acting modules can be molded by natural selection to create a sizeable number of novel phenotypes. Results from decades of research indicate that developmental and phenotypic divergence among eukaryotic organisms is driven primarily by variation in levels of gene expression that are dictated by mutations, either in structural or regulatory regions, of genes. The relative contributions and interplay of cis- and trans-acting regulatory factors to this evolutionary process, however, remain poorly understood. Analysis of eight genes in the Bz1-Sh1 interval of Zea mays (maize) indicates significant allele-specific expression biases in at least one tissue for all genes, ranging from 1.3-fold to 36-fold. All detected effects were cis-regulatory in nature, although genetic background may also influence the level of expression bias and tissue specificity for some allelic combinations. Most allelic pairs exhibited the same direction and approximate intensity of bias across all four tissues; however, a subset of allelic pairs show alternating dominance across different tissue types or variation in the degree of bias in different tissues. In addition, the genes showing the most striking levels of allelic bias co-localize with a previously described recombination hotspot in this region, suggesting a naturally occurring genetic mechanism for creating regulatory variability for a subset of plant genes that may ultimately lead to evolutionary diversification.
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The contributions of transposable elements to the structure, function, and evolution of plant genomes.
Annu Rev Plant Biol
PUBLISHED: 02-21-2014
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Transposable elements (TEs) are the key players in generating genomic novelty by a combination of the chromosome rearrangements they cause and the genes that come under their regulatory sway. Genome size, gene content, gene order, centromere function, and numerous other aspects of nuclear biology are driven by TE activity. Although the origins and attitudes of TEs have the hallmarks of selfish DNA, there are numerous cases where TE components have been co-opted by the host to create new genes or modify gene regulation. In particular, epigenetic regulation has been transformed from a process to silence invading TEs and viruses into a key strategy for regulating plant genes. Most, perhaps all, of this epigenetic regulation is derived from TE insertions near genes or TE-encoded factors that act in trans. Enormous pools of genome data and new technologies for reverse genetics will lead to a powerful new era of TE analysis in plants.
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Whole plastome sequences from five ginger species facilitate marker development and define limits to barcode methodology.
PLoS ONE
PUBLISHED: 01-01-2014
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Plants from the Zingiberaceae family are a key source of spices and herbal medicines. Species identification within this group is critical in the search for known and possibly novel bioactive compounds. To facilitate precise characterization of this group, we have sequenced chloroplast genomes from species representing five major groups within Zingiberaceae. Generally, the structure of these genomes is similar to the basal angiosperm excepting an expansion of 3 kb associated with the inverted repeat A region. Portions of this expansion appear to be shared across the entire Zingiberales order, which includes gingers and bananas. We used whole plastome alignment information to develop DNA barcodes that would maximize the ability to differentiate species within the Zingiberaceae. Our computation pipeline identified regions of high variability that were flanked by highly conserved regions used for primer design. This approach yielded hitherto unexploited regions of variability. These theoretically optimal barcodes were tested on a range of species throughout the family and were found to amplify and differentiate genera and, in some cases, species. Still, though these barcodes were specifically optimized for the Zingiberaceae, our data support the emerging consensus that whole plastome sequences are needed for robust species identification and phylogenetics within this family.
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Genomic resources for gene discovery, functional genome annotation, and evolutionary studies of maize and its close relatives.
Genetics
PUBLISHED: 09-13-2013
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Maize is one of the most important food crops and a key model for genetics and developmental biology. A genetically anchored and high-quality draft genome sequence of maize inbred B73 has been obtained to serve as a reference sequence. To facilitate evolutionary studies in maize and its close relatives, much like the Oryza Map Alignment Project (OMAP) (www.OMAP.org) bacterial artificial chromosome (BAC) resource did for the rice community, we constructed BAC libraries for maize inbred lines Zheng58, Chang7-2, and Mo17 and maize wild relatives Zea mays ssp. parviglumis and Tripsacum dactyloides. Furthermore, to extend functional genomic studies to maize and sorghum, we also constructed binary BAC (BIBAC) libraries for the maize inbred B73 and the sorghum landrace Nengsi-1. The BAC/BIBAC vectors facilitate transfer of large intact DNA inserts from BAC clones to the BIBAC vector and functional complementation of large DNA fragments. These seven Zea Map Alignment Project (ZMAP) BAC/BIBAC libraries have average insert sizes ranging from 92 to 148 kb, organellar DNA from 0.17 to 2.3%, empty vector rates between 0.35 and 5.56%, and genome equivalents of 4.7- to 8.4-fold. The usefulness of the Parviglumis and Tripsacum BAC libraries was demonstrated by mapping clones to the reference genome. Novel genes and alleles present in these ZMAP libraries can now be used for functional complementation studies and positional or homology-based cloning of genes for translational genomics.
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Isolation and bioinformatic analysis of a novel transposable element, ISCbe4, from the hyperthermophilic bacterium, Caldicellulosiruptor bescii.
J. Ind. Microbiol. Biotechnol.
PUBLISHED: 08-02-2013
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Caldicellulosiruptor bescii is an anaerobic thermophilic bacterium of special interest for use in the consolidated bioprocessing of plant biomass to biofuels. In the course of experiments to engineer pyruvate metabolism in C. bescii, we isolated a mutant of C. bescii that contained an insertion in the L-lactate dehydrogenase gene (ldh). PCR amplification and sequencing of the ldh gene from this mutant revealed a 1,609-bp insertion that contained a single open reading frame of 479 amino acids (1,440 bp) annotated as a hypothetical protein with unknown function. The ORF is flanked by an 8-base direct repeat sequence. Bioinformatic analysis indicated that this ORF is part of a novel transposable element, ISCbe4, which is only intact in the genus Caldicellulosiruptor, but has ancient relatives that are present in degraded (and previously unrecognized) forms across many bacterial and archaeal clades.
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Isolation and diversity analysis of resistance gene homologues from switchgrass.
G3 (Bethesda)
PUBLISHED: 04-17-2013
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Resistance gene homologs (RGHs) were isolated from the switchgrass variety Alamo by a combination of polymerase chain reaction and expressed sequence tag (EST) database mining. Fifty-eight RGHs were isolated by polymerase chain reaction and 295 RGHs were identified in 424,545 switchgrass ESTs. Four nucleotide binding site--leucine-rich repeat RGHs were selected to investigate RGH haplotypic diversity in seven switchgrass varieties chosen for their representation of a broad range of the switchgrass germplasm. Lowland and upland ecotypes were found to be less similar, even from nearby populations, than were more distant populations with similar growth environments. Most (83.5%) of the variability in these four RGHs was found to be attributable to the within-population component. The difference in nucleotide diversity between and within populations was observed to be small, whereas this diversity is maintained to similar degrees at both population and ecotype levels. The results also revealed that the analyzed RGHs were under positive selection in the studied switchgrass accessions. Intragenic recombination was detected in switchgrass RGHs, thereby demonstrating an active genetic process that has the potential to generate new resistance genes with new specificities that might act against newly-arising pathogen races.
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Permanent genetic resources added to molecular ecology resources database 1 October 2012-30 November 2012.
Mol Ecol Resour
PUBLISHED: 01-25-2013
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This article documents the addition of 153 microsatellite marker loci to the Molecular Ecology Resources Database. Loci were developed for the following species: Brassica oleracea, Brycon amazonicus, Dimorphandra wilsonii, Eupallasella percnurus, Helleborus foetidus, Ipomoea purpurea, Phrynops geoffroanus, Prochilodus argenteus, Pyura sp., Sylvia atricapilla, Teratosphaeria suttonii, Trialeurodes vaporariorum and Trypanosoma brucei. These loci were cross-tested on the following species: Dimorphandra coccicinea, Dimorphandra cuprea, Dimorphandra gardneriana, Dimorphandra jorgei, Dimorphandra macrostachya, Dimorphandra mollis, Dimorphandra parviflora and Dimorphandra pennigera.
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Fine-mapping and identification of a candidate gene underlying the d2 dwarfing phenotype in pearl millet, Cenchrus americanus (L.) Morrone.
G3 (Bethesda)
PUBLISHED: 01-15-2013
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Pearl millet is one of the most important subsistence crops grown in India and sub-Saharan Africa. In many cereal crops, reduced height is a key trait for enhancing yield, and dwarf mutants have been extensively used in breeding to reduce yield loss due to lodging under intense management. In pearl millet, the recessive d2 dwarfing gene has been deployed widely in commercial germplasm grown in India, the United States, and Australia. Despite its importance, very little research has gone into determining the identity of the d2 gene. We used comparative information, genetic mapping in two F2 populations representing a total of some 1500 progeny, and haplotype analysis of three tall and three dwarf inbred lines to delineate the d2 region by two genetic markers that, in sorghum, define a region of 410 kb with 40 annotated genes. One of the sorghum genes annotated within this region is ABCB1, which encodes a P-glycoprotein involved in auxin transport. This gene had previously been shown to underlie the economically important dw3 dwarf mutation in sorghum. The cosegregation of ABCB1 with the d2 phenotype, its differential expression in the tall inbred ICMP 451 and the dwarf inbred Tift 23DB, and the similar phenotype of stacked lower internodes in the sorghum dw3 and pearl millet d2 mutants suggest that ABCB1 is a likely candidate for d2.
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Dynamic gene copy number variation in collinear regions of grass genomes.
Mol. Biol. Evol.
PUBLISHED: 10-14-2011
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A salient feature of genomes of higher organisms is the birth and death of gene copies. An example is the alpha prolamin genes, which encode seed storage proteins in grasses (Poaceae) and represent a medium-size gene family. To better understand the mechanism, extent, and pace of gene amplification, we compared prolamin gene copies in the genomes of two different tribes in the Panicoideae, the Paniceae and the Andropogoneae. We identified alpha prolamin (setarin) gene copies in the diploid foxtail millet (Paniceae) genome (490 Mb) and compared them with orthologous regions in diploid sorghum (730 Mb) and ancient allotetraploid maize (2,300 Mb) (Andropogoneae). Because sequenced genomes of other subfamilies of Poaceae like rice (389 Mb) (Ehrhartoideae) and Brachypodium (272 Mb) (Pooideae) do not have alpha prolamin genes, their collinear regions can serve as "empty" reference sites. A pattern emerged, where genes were copied and inserted into other chromosomal locations followed by additional tandem duplications (clusters). We observed both recent (species-specific) insertion events and older ones that are shared by these tribes. Many older copies were deleted by unequal crossing over of flanking sequences or damaged by truncations. However, some remain intact with active and inactive alleles. These results indicate that genomes reflect only a snapshot of the gene content of a species and are far less static than conventional genetics has suggested. Nucleotide substitution rates for active alpha prolamins genes were twice as high as for low copy number beta, gamma, and delta prolamin genes, suggesting that gene amplification accelerates the pace of divergence.
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The Selaginella genome identifies genetic changes associated with the evolution of vascular plants.
Jo Ann Banks, Tomoaki Nishiyama, Mitsuyasu Hasebe, John L Bowman, Michael Gribskov, Claude dePamphilis, Victor A Albert, Naoki Aono, Tsuyoshi Aoyama, Barbara A Ambrose, Neil W Ashton, Michael J Axtell, Elizabeth Barker, Michael S Barker, Jeffrey L Bennetzen, Nicholas D Bonawitz, Clint Chapple, Chaoyang Cheng, Luiz Gustavo Guedes Corrêa, Michael Dacre, Jeremy DeBarry, Ingo Dreyer, Marek Eliáš, Eric M Engstrom, Mark Estelle, Liang Feng, Cédric Finet, Sandra K Floyd, Wolf B Frommer, Tomomichi Fujita, Lydia Gramzow, Michael Gutensohn, Jesper Harholt, Mitsuru Hattori, Alexander Heyl, Tadayoshi Hirai, Yuji Hiwatashi, Masaki Ishikawa, Mineko Iwata, Kenneth G Karol, Barbara Koehler, Uener Kolukisaoglu, Minoru Kubo, Tetsuya Kurata, Sylvie Lalonde, Kejie Li, Ying Li, Amy Litt, Eric Lyons, Gerard Manning, Takeshi Maruyama, Todd P Michael, Koji Mikami, Saori Miyazaki, Shin-Ichi Morinaga, Takashi Murata, Bernd Mueller-Roeber, David R Nelson, Mari Obara, Yasuko Oguri, Richard G Olmstead, Naoko Onodera, Bent Larsen Petersen, Birgit Pils, Michael Prigge, Stefan A Rensing, Diego Mauricio Riaño-Pachón, Alison W Roberts, Yoshikatsu Sato, Henrik Vibe Scheller, Burkhard Schulz, Christian Schulz, Eugene V Shakirov, Nakako Shibagaki, Naoki Shinohara, Dorothy E Shippen, Iben Sørensen, Ryo Sotooka, Nagisa Sugimoto, Mamoru Sugita, Naomi Sumikawa, Milos Tanurdzic, Günter Theißen, Peter Ulvskov, Sachiko Wakazuki, Jing-Ke Weng, William W G T Willats, Daniel Wipf, Paul G Wolf, Lixing Yang, Andreas D Zimmer, Qihui Zhu, Therese Mitros, Uffe Hellsten, Dominique Loqué, Robert Otillar, Asaf Salamov, Jeremy Schmutz, Harris Shapiro, Erika Lindquist, Susan Lucas, Daniel Rokhsar, Igor V Grigoriev.
Science
PUBLISHED: 05-05-2011
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Vascular plants appeared ~410 million years ago, then diverged into several lineages of which only two survive: the euphyllophytes (ferns and seed plants) and the lycophytes. We report here the genome sequence of the lycophyte Selaginella moellendorffii (Selaginella), the first nonseed vascular plant genome reported. By comparing gene content in evolutionarily diverse taxa, we found that the transition from a gametophyte- to a sporophyte-dominated life cycle required far fewer new genes than the transition from a nonseed vascular to a flowering plant, whereas secondary metabolic genes expanded extensively and in parallel in the lycophyte and angiosperm lineages. Selaginella differs in posttranscriptional gene regulation, including small RNA regulation of repetitive elements, an absence of the trans-acting small interfering RNA pathway, and extensive RNA editing of organellar genes.
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Switchgrass (Panicum virgatum L.) polyubiquitin gene (PvUbi1 and PvUbi2) promoters for use in plant transformation.
BMC Biotechnol.
PUBLISHED: 04-20-2011
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The ubiquitin protein is present in all eukaryotic cells and promoters from ubiquitin genes are good candidates to regulate the constitutive expression of transgenes in plants. Therefore, two switchgrass (Panicum virgatum L.) ubiquitin genes (PvUbi1 and PvUbi2) were cloned and characterized. Reporter constructs were produced containing the isolated 5 upstream regulatory regions of the coding sequences (i.e. PvUbi1 and PvUbi2 promoters) fused to the uidA coding region (GUS) and tested for transient and stable expression in a variety of plant species and tissues.
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De novo genome sequencing and comparative genomics of date palm (Phoenix dactylifera).
Nat. Biotechnol.
PUBLISHED: 02-17-2011
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Date palm is one of the most economically important woody crops cultivated in the Middle East and North Africa and is a good candidate for improving agricultural yields in arid environments. Nonetheless, long generation times (5-8 years) and dioecy (separate male and female trees) have complicated its cultivation and genetic analysis. To address these issues, we assembled a draft genome for a Khalas variety female date palm, the first publicly available resource of its type for a member of the order Arecales. The ?380 Mb sequence, spanning mainly gene-rich regions, includes >25,000 gene models and is predicted to cover ?90% of genes and ?60% of the genome. Sequencing of eight other cultivars, including females of the Deglet Noor and Medjool varieties and their backcrossed males, identified >3.5 million polymorphic sites, including >10,000 genic copy number variations. A small subset of these polymorphisms can distinguish multiple varieties. We identified a region of the genome linked to gender and found evidence that date palm employs an XY system of gender inheritance.
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Transposable element origins of epigenetic gene regulation.
Curr. Opin. Plant Biol.
PUBLISHED: 01-14-2011
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Transposable elements (TEs) are massively abundant and unstable in all plant genomes, but are mostly silent because of epigenetic suppression. Because all known epigenetic pathways act on all TEs, it is likely that the specialized epigenetic regulation of regular host genes (RHGs) was co-opted from this ubiquitous need for the silencing of TEs and viruses. With their internally repetitive and rearranging structures, and the acquisition of fragments of RHGs, the expression of TEs commonly makes antisense RNAs for both TE genes and RHGs. These antisense RNAs, particularly from heterochromatic reservoirs of zombie TEs that are rearranged to form variously internally repetitive structures, may be advantageous because their induction will help rapidly suppress active TEs of the same family. RHG fragments within rapidly rearranging TEs may also provide the raw material for the ongoing generation of miRNA genes. TE gene expression is regulated by both environmental and developmental signals, and insertions can place nearby RHGs under the regulation (both standard and epigenetic) of the TE. The ubiquity of TEs, their frequent preferential association with RHGs, and their ability to be programmed by epigenetic signals all indicate that RGHs have nearly unlimited access to novel regulatory cassettes to assist plant adaptation.
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Permanent Genetic Resources added to Molecular Ecology Resources Database 1 April 2010 - 31 May 2010.
, K Andree, Jan Axtner, M J Bagley, E J Barlow, T J C Beebee, Jeffrey L Bennetzen, Eldredge Bermingham, M C Boisselier-Dubayle, Christine A Bozarth, Christopher P Brooks, R P Brown, Gaetano Catanese, S Cavers, Ivania Cerón-Souza, Solomon T C Chak, M N Chan, P Charles-Dominique, C Y Chen, J D Chen, Leah Chinchilla, D DA Silva, S Dafreville, F Daunt, H Delatte, T Dorge, N Duncan, J D Durand, D Duvernell, Matt Estep, Sigang Fan, R Fattahi, Oscar Flores Villela, Yokking Fong, H Fréville, Victoria Funes, C Gallardo-Escarate, K N Ganeshaiah, M R Ghaffari, C Girod, B J Gomez-Moliner, Gracia P Gonzalez-Porter, A Gosa, F Govers, F Guérin, Diarah Guindo, Frank Hailer, P A Haye, Kim A Hoelmer, S Hofmann, Yan Hong, Chaoqun Hu, S W Huang, L Humeau, Carlos Infante, S A Jackson, E Jacobsen, A Jowkar, M Kafi, M J Kermani, Hyojoong Kim, Kyung Seok Kim, Min-Young Kim, W Knibb, Ousmane A Koita, H Korpelainen, J Lambourdiere, Eloisa Lasso, R Leblois, Hang Lee, Seunghwan Lee, F C C Leung, Kenneth M Y Leung, Chunhong Li, Y Li, Dietmar Lieckfeldt, M Lizana, W J Loughry, Peng Luo, M J Madeira, P Mahmoodi, Jesus E Maldonado, M Mardi, O Mendes, G Miehe, Peter Muth, D Nacci, L Naveen Kumar, Wai-Chuen Ng, T Pailler, Heiko K Parzies, Laura Perez, M Pfunder, M Pietiläinen, S M Pirseyedi, D Porta, J Porta, J M Porta, S Quilici, F P Rakotoarivelo, B T Ramesha, G Ravikanth, B Riéra, A M Risterucci, D A Roberts, S Samadi, V Sarasola-Puente, E Sarrazin, C Sarthou, Anke Schmidt, N I Segovia, K N Shen, C Simiand, Muhammad Hidayat Bin Sman, T Solhoy, Simone Sommer, R C Sumangala, Ramona Taubert, T Tejangkura, A Telford, A Testa, C Tollon-Cordet, W N Tzeng, R Uma Shaanker, T A J Van Der Lee, Thomas A VAN Mourik, R Vasudeva, T C Wai, R L Wang, Mark E Welch, Eva Weltzien, A Whitehead, Anastasia Woodard, Jianjun Xia, M Zeinolabedini, Lvping Zhang.
Mol Ecol Resour
PUBLISHED: 09-26-2010
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This article documents the addition of 396 microsatellite marker loci to the Molecular Ecology Resources Database. Loci were developed for the following species: Anthocidaris crassispina, Aphis glycines, Argyrosomus regius, Astrocaryum sciophilum, Dasypus novemcinctus, Delomys sublineatus, Dermatemys mawii, Fundulus heteroclitus, Homalaspis plana, Jumellea rossii, Khaya senegalensis, Mugil cephalus, Neoceratitis cyanescens, Phalacrocorax aristotelis, Phytophthora infestans, Piper cordulatum, Pterocarpus indicus, Rana dalmatina, Rosa pulverulenta, Saxifraga oppositifolia, Scomber colias, Semecarpus kathalekanensis, Stichopus monotuberculatus, Striga hermonthica, Tarentola boettgeri and Thermophis baileyi. These loci were cross-tested on the following species: Aphis gossypii, Sooretamys angouya, Euryoryzomys russatus, Fundulus notatus, Fundulus olivaceus, Fundulus catenatus, Fundulus majalis, Jumellea fragrans, Jumellea triquetra Jumellea recta, Jumellea stenophylla, Liza richardsonii, Piper marginatum, Piper aequale, Piper darienensis, Piper dilatatum, Rana temporaria, Rana iberica, Rana pyrenaica, Semecarpus anacardium, Semecarpus auriculata, Semecarpus travancorica, Spondias acuminata, Holigarna grahamii, Holigarna beddomii, Mangifera indica, Anacardium occidentale, Tarentola delalandii, Tarentola caboverdianus and Thermophis zhaoermii.
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The genome of woodland strawberry (Fragaria vesca).
Nat. Genet.
PUBLISHED: 06-09-2010
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The woodland strawberry, Fragaria vesca (2n = 2x = 14), is a versatile experimental plant system. This diminutive herbaceous perennial has a small genome (240 Mb), is amenable to genetic transformation and shares substantial sequence identity with the cultivated strawberry (Fragaria × ananassa) and other economically important rosaceous plants. Here we report the draft F. vesca genome, which was sequenced to ×39 coverage using second-generation technology, assembled de novo and then anchored to the genetic linkage map into seven pseudochromosomes. This diploid strawberry sequence lacks the large genome duplications seen in other rosids. Gene prediction modeling identified 34,809 genes, with most being supported by transcriptome mapping. Genes critical to valuable horticultural traits including flavor, nutritional value and flowering time were identified. Macrosyntenic relationships between Fragaria and Prunus predict a hypothetical ancestral Rosaceae genome that had nine chromosomes. New phylogenetic analysis of 154 protein-coding genes suggests that assignment of Populus to Malvidae, rather than Fabidae, is warranted.
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Spatio-temporal patterns of genome evolution in allotetraploid species of the genus Oryza.
Plant J.
PUBLISHED: 05-06-2010
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Summary Despite knowledge that polyploidy is widespread and a major evolutionary force in flowering plant diversification, detailed comparative molecular studies on polyploidy have been confined to only a few species and families. The genus Oryza is composed of 23 species that are classified into ten distinct genome types (six diploid and four polyploid), and is emerging as a powerful new model system to study polyploidy. Here we report the identification, sequence and comprehensive comparative annotation of eight homoeologous genomes from a single orthologous region (Adh1-Adh2) from four allopolyploid species representing each of the known Oryza genome types (BC, CD, HJ and KL). Detailed comparative phylogenomic analyses of these regions within and across species and ploidy levels provided several insights into the spatio-temporal dynamics of genome organization and evolution of this region in natural polyploids of Oryza. The major findings of this study are that: (i) homoeologous genomic regions within the same nucleus experience both independent and parallel evolution, (ii) differential lineage-specific selection pressures do not occur between polyploids and their diploid progenitors, (iii) there have been no dramatic structural changes relative to the diploid ancestors, (iv) a variation in the molecular evolutionary rate exists between the two genomes in the BC complex species even though the BC and CD polyploid species appear to have arisen <2 million years ago, and (v) there are no clear distinctions in the patterns of genome evolution in the diploid versus polyploid species.
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An examination of targeted gene neighborhoods in strawberry.
BMC Plant Biol.
PUBLISHED: 05-04-2010
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Strawberry (Fragaria spp.) is the familiar name of a group of economically important crop plants and wild relatives that also represent an emerging system for the study of gene and genome evolution. Its small stature, rapid seed-to-seed cycle, transformability and miniscule basic genome make strawberry an attractive system to study processes related to plant physiology, development and crop production; yet it lacks substantial genomics-level resources. This report addresses this deficiency by characterizing 0.71 Mbp of gene space from a diploid species (F. vesca). The twenty large genomic tracks (30-52 kb) captured as fosmid inserts comprise gene regions with roles in flowering, disease resistance, and metabolism.
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The B73 maize genome: complexity, diversity, and dynamics.
Patrick S Schnable, Doreen Ware, Robert S Fulton, Joshua C Stein, Fusheng Wei, Shiran Pasternak, Chengzhi Liang, Jianwei Zhang, Lucinda Fulton, Tina A Graves, Patrick Minx, Amy Denise Reily, Laura Courtney, Scott S Kruchowski, Chad Tomlinson, Cindy Strong, Kim Delehaunty, Catrina Fronick, Bill Courtney, Susan M Rock, Eddie Belter, Feiyu Du, Kyung Kim, Rachel M Abbott, Marc Cotton, Andy Levy, Pamela Marchetto, Kerri Ochoa, Stephanie M Jackson, Barbara Gillam, Weizu Chen, Le Yan, Jamey Higginbotham, Marco Cardenas, Jason Waligorski, Elizabeth Applebaum, Lindsey Phelps, Jason Falcone, Krishna Kanchi, Thynn Thane, Adam Scimone, Nay Thane, Jessica Henke, Tom Wang, Jessica Ruppert, Neha Shah, Kelsi Rotter, Jennifer Hodges, Elizabeth Ingenthron, Matt Cordes, Sara Kohlberg, Jennifer Sgro, Brandon Delgado, Kelly Mead, Asif Chinwalla, Shawn Leonard, Kevin Crouse, Kristi Collura, Dave Kudrna, Jennifer Currie, Ruifeng He, Angelina Angelova, Shanmugam Rajasekar, Teri Mueller, Rene Lomeli, Gabriel Scara, Ara Ko, Krista Delaney, Marina Wissotski, Georgina Lopez, David Campos, Michele Braidotti, Elizabeth Ashley, Wolfgang Golser, Hyeran Kim, Seunghee Lee, Jinke Lin, Zeljko Dujmic, Woojin Kim, Jayson Talag, Andrea Zuccolo, Chuanzhu Fan, Aswathy Sebastian, Melissa Kramer, Lori Spiegel, Lidia Nascimento, Theresa Zutavern, Beth Miller, Claude Ambroise, Stephanie Müller, Will Spooner, Apurva Narechania, Liya Ren, Sharon Wei, Sunita Kumari, Ben Faga, Michael J Levy, Linda McMahan, Peter Van Buren, Matthew W Vaughn, Kai Ying, Cheng-Ting Yeh, Scott J Emrich, Yi Jia, Ananth Kalyanaraman, An-Ping Hsia, W Brad Barbazuk, Regina S Baucom, Thomas P Brutnell, Nicholas C Carpita, Cristian Chaparro, Jer-Ming Chia, Jean-Marc Deragon, James C Estill, Yan Fu, Jeffrey A Jeddeloh, Yujun Han, Hyeran Lee, Pinghua Li, Damon R Lisch, Sanzhen Liu, Zhijie Liu, Dawn Holligan Nagel, Maureen C McCann, Phillip SanMiguel, Alan M Myers, Dan Nettleton, John Nguyen, Bryan W Penning, Lalit Ponnala, Kevin L Schneider, David C Schwartz, Anupma Sharma, Carol Soderlund, Nathan M Springer, Qi Sun, Hao Wang, Michael Waterman, Richard Westerman, Thomas K Wolfgruber, Lixing Yang, Yeisoo Yu, Lifang Zhang, Shiguo Zhou, Qihui Zhu, Jeffrey L Bennetzen, R Kelly Dawe, Jiming Jiang, Ning Jiang, Gernot G Presting, Susan R Wessler, Srinivas Aluru, Robert A Martienssen, Sandra W Clifton, W Richard McCombie, Rod A Wing, Richard K Wilson.
Science
PUBLISHED: 12-08-2009
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We report an improved draft nucleotide sequence of the 2.3-gigabase genome of maize, an important crop plant and model for biological research. Over 32,000 genes were predicted, of which 99.8% were placed on reference chromosomes. Nearly 85% of the genome is composed of hundreds of families of transposable elements, dispersed nonuniformly across the genome. These were responsible for the capture and amplification of numerous gene fragments and affect the composition, sizes, and positions of centromeres. We also report on the correlation of methylation-poor regions with Mu transposon insertions and recombination, and copy number variants with insertions and/or deletions, as well as how uneven gene losses between duplicated regions were involved in returning an ancient allotetraploid to a genetically diploid state. These analyses inform and set the stage for further investigations to improve our understanding of the domestication and agricultural improvements of maize.
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Distribution, diversity, evolution, and survival of Helitrons in the maize genome.
Proc. Natl. Acad. Sci. U.S.A.
PUBLISHED: 11-19-2009
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Homology and structure-based approaches were used to identify Helitrons in the genome of maize inbred B73. A total of 1,930 intact Helitrons from eight families (62 subfamilies) and >20,000 Helitron fragments were identified, accounting for approximately 2.2% of the B73 genome. Transposition of at least one of these families is ongoing, but the most prominent burst of amplification activity was approximately 250,000 years ago. Sixty percent of maize Helitrons were found to have captured fragments of nuclear genes ( approximately 840 different fragment acquisitions, with tens of thousands of predicted gene fragments inside Helitrons within the B73 assembly). Most acquired gene fragments are undergoing random drift, but 4% were calculated to be under purifying selection, whereas another 4% exhibit apparent adaptive selection, suggesting beneficial effects for the host or Helitron transposition/retention. Gene fragment capture is frequent in some Helitron subfamilies, with as many as 10 unlinked genes providing DNA inserts within a single element. Gene fragment acquisition appears to positively influence element survival and/or ability of the Helitron to acquire additional gene fragments. Helitrons with gene fragment captures in the antisense orientation have a lesser chance of survival. Helitron distribution in maize exhibits severe biases, including preferential accumulation in relatively gene-rich regions. Insertions, however, are not usually found inside genes. Rather, Helitrons preferentially insert near (but not into) other Helitrons. This biased accumulation is not caused by a preference for cis or nearby transposition, suggesting a specific association between Helitron integration functions and unknown chromatin characteristics that specifically mark Helitrons.
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Do genetic recombination and gene density shape the pattern of DNA elimination in rice long terminal repeat retrotransposons?
Genome Res.
PUBLISHED: 09-29-2009
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In flowering plants, the accumulation of small deletions through unequal homologous recombination (UR) and illegitimate recombination (IR) is proposed to be the major process counteracting genome expansion, which is caused primarily by the periodic amplification of long terminal repeat retrotransposons (LTR-RTs). However, the full suite of evolutionary forces that govern the gain or loss of transposable elements (TEs) and their distribution within a genome remains unclear. Here, we investigated the distribution and structural variation of LTR-RTs in relation to the rates of local genetic recombination (GR) and gene densities in the rice (Oryza sativa) genome. Our data revealed a positive correlation between GR rates and gene densities and negative correlations between LTR-RT densities and both GR and gene densities. The data also indicate a tendency for LTR-RT elements and fragments to be shorter in regions with higher GR rates; the size reduction of LTR-RTs appears to be achieved primarily through solo LTR formation by UR. Comparison of indica and japonica rice revealed patterns and frequencies of LTR-RT gain and loss within different evolutionary timeframes. Different LTR-RT families exhibited variable distribution patterns and structural changes, but overall LTR-RT compositions and genes were organized according to the GR gradients of the genome. Further investigation of non-LTR-RTs and DNA transposons revealed a negative correlation between gene densities and the abundance of DNA transposons and a weak correlation between GR rates and the abundance of long interspersed nuclear elements (LINEs)/short interspersed nuclear elements (SINEs). Together, these observations suggest that GR and gene density play important roles in shaping the dynamic structure of the rice genome.
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Exceptional diversity, non-random distribution, and rapid evolution of retroelements in the B73 maize genome.
PLoS Genet.
PUBLISHED: 08-25-2009
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Recent comprehensive sequence analysis of the maize genome now permits detailed discovery and description of all transposable elements (TEs) in this complex nuclear environment. Reiteratively optimized structural and homology criteria were used in the computer-assisted search for retroelements, TEs that transpose by reverse transcription of an RNA intermediate, with the final results verified by manual inspection. Retroelements were found to occupy the majority (>75%) of the nuclear genome in maize inbred B73. Unprecedented genetic diversity was discovered in the long terminal repeat (LTR) retrotransposon class of retroelements, with >400 families (>350 newly discovered) contributing >31,000 intact elements. The two other classes of retroelements, SINEs (four families) and LINEs (at least 30 families), were observed to contribute 1,991 and approximately 35,000 copies, respectively, or a combined approximately 1% of the B73 nuclear genome. With regard to fully intact elements, median copy numbers for all retroelement families in maize was 2 because >250 LTR retrotransposon families contained only one or two intact members that could be detected in the B73 draft sequence. The majority, perhaps all, of the investigated retroelement families exhibited non-random dispersal across the maize genome, with LINEs, SINEs, and many low-copy-number LTR retrotransposons exhibiting a bias for accumulation in gene-rich regions. In contrast, most (but not all) medium- and high-copy-number LTR retrotransposons were found to preferentially accumulate in gene-poor regions like pericentromeric heterochromatin, while a few high-copy-number families exhibited the opposite bias. Regions of the genome with the highest LTR retrotransposon density contained the lowest LTR retrotransposon diversity. These results indicate that the maize genome provides a great number of different niches for the survival and procreation of a great variety of retroelements that have evolved to differentially occupy and exploit this genomic diversity.
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Detailed analysis of a contiguous 22-Mb region of the maize genome.
PLoS Genet.
PUBLISHED: 08-21-2009
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Most of our understanding of plant genome structure and evolution has come from the careful annotation of small (e.g., 100 kb) sequenced genomic regions or from automated annotation of complete genome sequences. Here, we sequenced and carefully annotated a contiguous 22 Mb region of maize chromosome 4 using an improved pseudomolecule for annotation. The sequence segment was comprehensively ordered, oriented, and confirmed using the maize optical map. Nearly 84% of the sequence is composed of transposable elements (TEs) that are mostly nested within each other, of which most families are low-copy. We identified 544 gene models using multiple levels of evidence, as well as five miRNA genes. Gene fragments, many captured by TEs, are prevalent within this region. Elimination of gene redundancy from a tetraploid maize ancestor that originated a few million years ago is responsible in this region for most disruptions of synteny with sorghum and rice. Consistent with other sub-genomic analyses in maize, small RNA mapping showed that many small RNAs match TEs and that most TEs match small RNAs. These results, performed on approximately 1% of the maize genome, demonstrate the feasibility of refining the B73 RefGen_v1 genome assembly by incorporating optical map, high-resolution genetic map, and comparative genomic data sets. Such improvements, along with those of gene and repeat annotation, will serve to promote future functional genomic and phylogenomic research in maize and other grasses.
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Structure-based discovery and description of plant and animal Helitrons.
Proc. Natl. Acad. Sci. U.S.A.
PUBLISHED: 07-21-2009
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Helitrons are recently discovered eukaryotic transposons that are predicted to amplify by a rolling-circle mechanism. They are present in most plant and animal species investigated, but were previously overlooked partly because they lack terminal repeats and do not create target site duplications. Helitrons are particularly abundant in flowering plants, where they frequently acquire, and sometimes express, 1 or more gene fragments. A structure-based search protocol was developed to find Helitrons and was used to analyze several plant and animal genomes, leading to the discovery of hundreds of new Helitrons. Analysis of these Helitrons has uncovered mechanisms of element evolution, including end creation and sequence acquisition. Preferential accumulation in gene-poor regions and target site specificities were also identified. Overall, these studies provide insights into the transposition and evolution of Helitrons and their contributions to evolved gene content and genome structure.
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The DAWGPAWS pipeline for the annotation of genes and transposable elements in plant genomes.
Plant Methods
PUBLISHED: 04-30-2009
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High quality annotation of the genes and transposable elements in complex genomes requires a human-curated integration of multiple sources of computational evidence. These evidences include results from a diversity of ab initio prediction programs as well as homology-based searches. Most of these programs operate on a single contiguous sequence at a time, and the results are generated in a diverse array of readable formats that must be translated to a standardized file format. These translated results must then be concatenated into a single source, and then presented in an integrated form for human curation.
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Biology and the beasts: individual investigator-driven research in the megaprojects era.
Trends Genet.
PUBLISHED: 04-25-2009
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Science funding over the past few decades has seen a shift from individual investigator research to the multi-investigator megaproject. But are these large projects the best approach to the life sciences or do they stifle creativity?
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Comparative sequence analysis of MONOCULM1-orthologous regions in 14 Oryza genomes.
Proc. Natl. Acad. Sci. U.S.A.
PUBLISHED: 01-22-2009
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Comparative genomics is a powerful tool to decipher gene and genome evolution. Placing multiple genome comparisons in a phylogenetic context improves the sensitivity of evolutionary inferences. In the genus Oryza, this comparative approach can be used to investigate gene function, genome evolution, domestication, polyploidy, and ecological adaptation. A large genomic region surrounding the MONOCULM1 (MOC1) locus was chosen for study in 14 Oryza species, including 10 diploids and 4 allotetraploids. Sequencing and annotation of 18 bacterial artificial chromosome clones for these species revealed highly conserved gene colinearity and structure in the MOC1 region. Since the Oryza radiation about 14 Mya, differences in transposon amplification appear to be responsible for the different current sizes of the Oryza genomes. In the MOC1 region, transposons were only conserved between genomes of the same type (e.g., AA or BB). In addition to the conserved gene content, several apparent genes have been generated de novo or uniquely retained in the AA lineage. Two different 3-gene segments have been inserted into the MOC1 region of O. coarctata (KK) or O. sativa by unknown mechanism(s). Large and apparently noncoding sequences flanking the MOC1 gene were observed to be under strong purifying selection. The allotetraploids Oryza alta and Oryza minuta were found to be products of recent polyploidization, less than 1.6 and 0.4 Mya, respectively. In allotetraploids, pseudogenization of duplicated genes was common, caused by large deletions, small frame-shifting insertions/deletions, or nonsense mutations.
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Natural selection on gene function drives the evolution of LTR retrotransposon families in the rice genome.
Genome Res.
PUBLISHED: 01-13-2009
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Although the proliferation of LTR retrotransposons can cause major genomic modification and reorganization, the evolutionary dynamics that affect their frequency in host genomes are poorly understood. We analyzed patterns of genetic variation among LTR retrotransposons from Oryza sativa to investigate the type of selective forces that potentially limit their amplification and subsequent population of a nuclear genome. We performed both intra- and interfamily analyses of patterns of molecular sequence variation across multiple LTR retrotransposon genes. This analysis involved more than 1000 LTR retrotransposon sequences from 14 separate families that varied in both their insertion dates and full-length copy numbers. We uncovered evidence of strong purifying selection across all gene regions, but also indications that rare episodes of positive selection and adaptation to the host genome occur. Furthermore, our results indicate that LTR retrotransposons exhibit different but predictable patterns of sequence variation depending on their date of transposition, suggesting that LTR retrotransposons, regardless of superfamily and family classifications, show similar "life-histories."
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Centromere retention and loss during the descent of maize from a tetraploid ancestor.
Proc. Natl. Acad. Sci. U.S.A.
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Although centromere function is highly conserved in eukaryotes, centromere sequences are highly variable. Only a few centromeres have been sequenced in higher eukaryotes because of their repetitive nature, thus hindering study of their structure and evolution. Conserved single-copy sequences in pericentromeres (CSCPs) of sorghum and maize were found to be diagnostic characteristics of adjacent centromeres. By analyzing comparative map data and CSCP sequences of sorghum, maize, and rice, the major evolutionary events related to centromere dynamics were discovered for the maize lineage after its divergence from a common ancestor with sorghum. (i) Remnants of ancient CSCP regions were found for the 10 lost ancestral centromeres, indicating that two ancient homeologous chromosome pairs did not contribute any centromeres to the current maize genome, whereas two other pairs contributed both of their centromeres. (ii) Five cases of long-distance, intrachromosome movement of CSCPs were detected in the retained centromeres, with inversion the major process involved. (iii) The 12 major chromosomal rearrangements that led to maize chromosome number reduction from 20 to 10 were uncovered. (iv) In addition to whole chromosome insertion near (but not always into) other centromeres, translocation and fusion were found to be important mechanisms underlying grass chromosome number reduction. (v) Comparison of chromosome structures confirms the polyploid event that led to the tetraploid ancestor of modern maize.
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The genome of the pear (Pyrus bretschneideri Rehd.).
Genome Res.
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The draft genome of the pear (Pyrus bretschneideri) using a combination of BAC-by-BAC and next-generation sequencing is reported. A 512.0-Mb sequence corresponding to 97.1% of the estimated genome size of this highly heterozygous species is assembled with 194× coverage. High-density genetic maps comprising 2005 SNP markers anchored 75.5% of the sequence to all 17 chromosomes. The pear genome encodes 42,812 protein-coding genes, and of these, ~28.5% encode multiple isoforms. Repetitive sequences of 271.9 Mb in length, accounting for 53.1% of the pear genome, are identified. Simulation of eudicots to the ancestor of Rosaceae has reconstructed nine ancestral chromosomes. Pear and apple diverged from each other ~5.4-21.5 million years ago, and a recent whole-genome duplication (WGD) event must have occurred 30-45 MYA prior to their divergence, but following divergence from strawberry. When compared with the apple genome sequence, size differences between the apple and pear genomes are confirmed mainly due to the presence of repetitive sequences predominantly contributed by transposable elements (TEs), while genic regions are similar in both species. Genes critical for self-incompatibility, lignified stone cells (a unique feature of pear fruit), sorbitol metabolism, and volatile compounds of fruit have also been identified. Multiple candidate SFB genes appear as tandem repeats in the S-locus region of pear; while lignin synthesis-related gene family expansion and highly expressed gene families of HCT, C3H, and CCOMT contribute to high accumulation of both G-lignin and S-lignin. Moreover, alpha-linolenic acid metabolism is a key pathway for aroma in pear fruit.
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High-throughput discovery of mutations in tef semi-dwarfing genes by next-generation sequencing analysis.
Genetics
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Tef (Eragrostis tef) is a major cereal crop in Ethiopia. Lodging is the primary constraint to increasing productivity in this allotetraploid species, accounting for losses of ?15-45% in yield each year. As a first step toward identifying semi-dwarf varieties that might have improved lodging resistance, an ?6× fosmid library was constructed and used to identify both homeologues of the dw3 semi-dwarfing gene of Sorghum bicolor. An EMS mutagenized population, consisting of ?21,210 tef plants, was planted and leaf materials were collected into 23 superpools. Two dwarfing candidate genes, homeologues of dw3 of sorghum and rht1 of wheat, were sequenced directly from each superpool with 454 technology, and 120 candidate mutations were identified. Out of 10 candidates tested, six independent mutations were validated by Sanger sequencing, including two predicted detrimental mutations in both dw3 homeologues with a potential to improve lodging resistance in tef through further breeding. This study demonstrates that high-throughput sequencing can identify potentially valuable mutations in under-studied plant species like tef and has provided mutant lines that can now be combined and tested in breeding programs for improved lodging resistance.
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G protein activation without a GEF in the plant kingdom.
PLoS Genet.
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Animal heterotrimeric G proteins are activated by guanine nucleotide exchange factors (GEF), typically seven transmembrane receptors that trigger GDP release and subsequent GTP binding. In contrast, the Arabidopsis thaliana G protein (AtGPA1) rapidly activates itself without a GEF and is instead regulated by a seven transmembrane Regulator of G protein Signaling (7TM-RGS) protein that promotes GTP hydrolysis to reset the inactive (GDP-bound) state. It is not known if this unusual activation is a major and constraining part of the evolutionary history of G signaling in eukaryotes. In particular, it is not known if this is an ancestral form or if this mechanism is maintained, and therefore constrained, within the plant kingdom. To determine if this mode of signal regulation is conserved throughout the plant kingdom, we analyzed available plant genomes for G protein signaling components, and we purified individually the plant components encoded in an informative set of plant genomes in order to determine their activation properties in vitro. While the subunits of the heterotrimeric G protein complex are encoded in vascular plant genomes, the 7TM-RGS genes were lost in all investigated grasses. Despite the absence of a G?-inactivating protein in grasses, all vascular plant G? proteins examined rapidly released GDP without a receptor and slowly hydrolyzed GTP, indicating that these G? are self-activating. We showed further that a single amino acid substitution found naturally in grass G? proteins reduced the G?-RGS interaction, and this amino acid substitution occurred before the loss of the RGS gene in the grass lineage. Like grasses, non-vascular plants also appear to lack RGS proteins. However, unlike grasses, one representative non-vascular plant G? showed rapid GTP hydrolysis, likely compensating for the loss of the RGS gene. Our findings, the loss of a regulatory gene and the retention of the "self-activating" trait, indicate the existence of divergent G? regulatory mechanisms in the plant kingdom. In the grasses, purifying selection on the regulatory gene was lost after the physical decoupling of the RGS protein and its cognate G? partner. More broadly these findings show extreme divergence in G? activation and regulation that played a critical role in the evolution of G protein signaling pathways.
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Reference genome sequence of the model plant Setaria.
Nat. Biotechnol.
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We generated a high-quality reference genome sequence for foxtail millet (Setaria italica). The ?400-Mb assembly covers ?80% of the genome and >95% of the gene space. The assembly was anchored to a 992-locus genetic map and was annotated by comparison with >1.3 million expressed sequence tag reads. We produced more than 580 million RNA-Seq reads to facilitate expression analyses. We also sequenced Setaria viridis, the ancestral wild relative of S. italica, and identified regions of differential single-nucleotide polymorphism density, distribution of transposable elements, small RNA content, chromosomal rearrangement and segregation distortion. The genus Setaria includes natural and cultivated species that demonstrate a wide capacity for adaptation. The genetic basis of this adaptation was investigated by comparing five sequenced grass genomes. We also used the diploid Setaria genome to evaluate the ongoing genome assembly of a related polyploid, switchgrass (Panicum virgatum).
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Haplotype Analysis and Linkage Disequilibrium at Five Loci in Eragrostis tef.
G3 (Bethesda)
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Eragrostis tef (Zucc.), a member of the Chloridoideae subfamily of grasses, is one of the most important food crops in Ethiopia. Lodging is the most important production problem in tef. The rht1 and sd1 dwarfing genes have been useful for improving lodging resistance in wheat and rice, respectively, in what has been known as the "Green Revolution." All homologs of rht1 and sd1 were cloned and sequenced from 31 tef accessions collected from across Ethiopia. The allotetraploid tef genome was found to carry two rht1 homologs. From sequence variation between these two putative homologs, an approximate ancestral divergence date of 6.4 million years ago was calculated for the two genomes within tef. Three sd1 homologs were identified in tef, with unknown orthologous/paralogous relationships. The genetic diversity in the 31 studied accessions was organized into a relatively small number of haplotypes (2-4) for four of these genes, whereas one rht1 homeologue exhibited 10 haplotypes. A low level of nucleotide diversity was observed at all loci. Linkage disequilibrium analysis demonstrated strong linkage disequilibrium, extending the length of the five genes investigated (2-4 kb), with no significant decline. There was no significant correlation between haplotypes of any of these genes and their recorded site of origin.
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