Differentiation processes in the primary root meristem are controlled by several signaling pathways that are regulated by phytohormones or by secreted peptides. Long-term maintenance of an active root meristem requires that the generation of new stem cells and the loss of these from the meristem due to differentiation are precisely coordinated. Via phenotypic and large-scale transcriptome analyses of mutants, we show that the signaling peptide CLE40 and the receptor proteins CLV2 and CRN act in two genetically separable pathways that antagonistically regulate cell differentiation in the proximal root meristem. CLE40 inhibits cell differentiation throughout the primary root meristem by controlling genes with roles in abscisic acid, auxin, and cytokinin signaling. CRN and CLV2 jointly control target genes that promote cell differentiation specifically in the transition zone of the proximal root meristem. While CRN and CLV2 are not acting in the CLE40 signaling pathway under normal growth conditions, both proteins are required when the levels of CLE40 or related CLE peptides increase. We show here that two antagonistically acting pathways controlling root meristem differentiation can be activated by the same peptide in a dosage-dependent manner.
C(4) photosynthesis outperforms the ancestral C(3) state in a wide range of natural and agro-ecosystems by affording higher water-use and nitrogen-use efficiencies. It therefore represents a prime target for engineering novel, high-yielding crops by introducing the trait into C(3) backgrounds. However, the genetic architecture of C(4) photosynthesis remains largely unknown. To define the divergence in gene expression modules between C(3) and C(4) photosynthesis during leaf ontogeny, we generated comprehensive transcriptome atlases of two Cleomaceae species, Gynandropsis gynandra (C(4)) and Tarenaya hassleriana (C(3)), by RNA sequencing. Overall, the gene expression profiles appear remarkably similar between the C(3) and C(4) species. We found that known C(4) genes were recruited to photosynthesis from different expression domains in C(3), including typical housekeeping gene expression patterns in various tissues as well as individual heterotrophic tissues. Furthermore, we identified a structure-related module recruited from the C(3) root. Comparison of gene expression patterns with anatomy during leaf ontogeny provided insight into genetic features of Kranz anatomy. Altered expression of developmental factors and cell cycle genes is associated with a higher degree of endoreduplication in enlarged C(4) bundle sheath cells. A delay in mesophyll differentiation apparent both in the leaf anatomy and the transcriptome allows for extended vein formation in the C(4) leaf.
Infective endocarditis is a life threatening complication of intravenous drug abuse, which continues to be a major burden with inadequately characterised long-term outcomes. We reviewed our institutional experience of surgical treatment of infective endocarditis in active intravenous drug abusers with the aim of identifying the determinants long-term outcome of this distinct subgroup of infective endocarditis patients.
Continuous growth and organ development from the shoot apical meristem (SAM) requires a precise coordination of stem cell proliferation, commitment of stem cell descendants to diverse differentiation pathways and establishment of morphological meristem-to-organ boundaries. These complex biological processes require extensive integration of several components of cell-to-cell signaling and gene regulatory networks whose coordinated actions have an impact on cell division and growth. Here we review the current knowledge of gene networks involved in organogenesis from the SAM in higher plants. We focus on recent advances to show how the interaction between transcriptional regulators, hormonal crosstalk and physical stress regulates the establishment and maintenance of meristem-to-organ boundaries. Continuous growth and organ development from the shoot apical meristem (SAM) requires a precise coordination of stem cell proliferation, commitment of stem cell descendants to diverse differentiation pathways and establishment of morphological meristem-to-organ boundaries. These complex biological processes require extensive integration of several components of cell-to-cell signaling and gene regulatory networks whose coordinated actions have an impact on cell division and growth. Here we review the current knowledge of gene networks involved in organogenesis from the SAM in higher plants. We focus on recent advances to show how the interaction between transcriptional regulators, hormonal crosstalk and physical stress regulates the establishment and maintenance of meristem-to-organ boundaries.
Significant aortic regurgitation (AR) after continuous-flow left ventricular assist device (cf-LVAD) placement affects device performance and patient outcomes. This study examined the development of AR and long-term results after implantation of cf-LVADs.
A bioartificial heart is a theoretical alternative to transplantation or mechanical left ventricular support. Native hearts decellularized with preserved architecture and vasculature may provide an acellular tissue platform for organ regeneration. We sought to develop a tissue-engineered whole-heart neoscaffold in human-sized porcine hearts.
Due to their rigid cell walls, plant cells can only communicate with each other either by symplastic transport of diverse non-cell autonomous signalling molecules via plasmodesmata (PDs) or by endo- and exocytosis of signalling molecules via the extracellular apoplastic space. PDs are plasma membrane-lined channels spanning the cell wall between neighbouring cells, allowing the exchange of molecules by symplastic movement through them. This review focuses on developmental decisions that are coordinated by short- and long-distance communication of cells via PDs. We propose a model combining both apoplastic and symplastic signalling events via secreted ligands and their PD-localized receptor kinases which gate the symplastic transport of information molecules through PDs. Cell communities can thus coordinate cell-fate decisions non-cell autonomously by connecting or disconnecting symplastic subdomains. Here we concentrate on the establishment of such subdomains in the plants primary meristems that serve to maintain long-lasting stem cell populations in the shoot and root apical meristems, and discuss how apoplastic signalling via transport of information molecules through PDs is integrated with symplastic feedback signalling events.
Upon hormonal signaling, ovules develop as lateral organs from the placenta. Ovule numbers ultimately determine the number of seeds that develop, and thereby contribute to the final seed yield in crop plants. We demonstrate here that CUP-SHAPED COTYLEDON 1 (CUC1), CUC2 and AINTEGUMENTA (ANT) have additive effects on ovule primordia formation. We show that expression of the CUC1 and CUC2 genes is required to redundantly regulate expression of PINFORMED1 (PIN1), which in turn is required for ovule primordia formation. Furthermore, our results suggest that the auxin response factor MONOPTEROS (MP/ARF5) may directly bind ANT, CUC1 and CUC2 and promote their transcription. Based on our findings, we propose an integrative model to describe the molecular mechanisms of the early stages of ovule development.
TBP-Associated Factors (TAFs) are components of complexes like TFIID, TFTC, SAGA/STAGA and SMAT that are important for the activation of transcription, either by establishing the basic transcription machinery or by facilitating histone acetylation. However, in Drosophila embryos several TAFs were shown to be associated with the Polycomb Repressive Complex 1 (PRC1), even though the role of this interaction remains unclear. Here we show that in Arabidopsis TAF13 interacts with MEDEA and SWINGER, both members of a plant variant of Polycomb Repressive Complex 2 (PRC2). PRC2 variants play important roles during the plant life cycle, including seed development. The taf13 mutation causes seed defects, showing embryo arrest at the 8-16 cell stage and over-proliferation of the endosperm in the chalazal region, which is typical for Arabidopsis PRC2 mutants. Our data suggest that TAF13 functions together with PRC2 in transcriptional regulation during seed development.
C? photosynthesis represents the most productive modes of photosynthesis in land plants and some of the most productive crops on the planet, such as maize and sugarcane, and many ecologically important native plants use this type of photosynthesis. Despite its ecological and economic importance, the genetic basis of C? photosynthesis remains largely unknown. Even many fundamental aspects of C? biochemistry, such as the molecular identity of solute transporters, and many aspects of C? plant leaf development, such as the Kranz anatomy, are currently not understood. Here, we review recent progress in gaining a mechanistic understanding of the complex C? trait through comparative evolutionary analyses of C? and C? species.
The root system of higher plants originates from the activity of a root meristem, which comprises a group of highly specialized and long-lasting stem cells. Their maintenance and number is controlled by the quiescent center (QC) cells and by feedback signaling from differentiated cells. Root meristems may have evolved from structurally distinct shoot meristems; however, no common player acting in stemness control has been found so far.
Land plants are characterised by haplo-diploid life cycles, and developing ovules are the organs in which the haploid and diploid generations coexist. Recently it has been shown that hormones such as auxin and cytokinins play important roles in ovule development and patterning. The establishment and regulation of auxin levels in cells is predominantly determined by the activity of the auxin efflux carrier proteins PIN-FORMED (PIN). To study the roles of PIN1 and PIN3 during ovule development we have used mutant alleles of both genes and also perturbed PIN1 and PIN3 expression using micro-RNAs controlled by the ovule specific DEFH9 (DEFIFICENS Homologue 9) promoter. PIN1 down-regulation and pin1-5 mutation severely affect female gametophyte development since embryo sacs arrest at the mono- and/or bi-nuclear stages (FG1 and FG3 stage). PIN3 function is not required for ovule development in wild-type or PIN1-silenced plants. We show that sporophytically expressed PIN1 is required for megagametogenesis, suggesting that sporophytic auxin flux might control the early stages of female gametophyte development, although auxin response is not visible in developing embryo sacs.
Multicellular organisms depend on cell production, cell fate specification, and correct patterning to shape their adult body. In plants, auxin plays a prominent role in the timely coordination of these different cellular processes. A well-studied example is lateral root initiation, in which auxin triggers founder cell specification and cell cycle activation of xylem pole-positioned pericycle cells. Here, we report that the E2Fa transcription factor of Arabidopsis thaliana is an essential component that regulates the asymmetric cell division marking lateral root initiation. Moreover, we demonstrate that E2Fa expression is regulated by the LATERAL ORGAN BOUNDARY DOMAIN18/LATERAL ORGAN BOUNDARY DOMAIN33 (LBD18/LBD33) dimer that is, in turn, regulated by the auxin signaling pathway. LBD18/LBD33 mediates lateral root organogenesis through E2Fa transcriptional activation, whereas E2Fa expression under control of the LBD18 promoter eliminates the need for LBD18. Besides lateral root initiation, vascular patterning is disrupted in E2Fa knockout plants, similarly as it is affected in auxin signaling and lbd mutants, indicating that the transcriptional induction of E2Fa through LBDs represents a general mechanism for auxin-dependent cell cycle activation. Our data illustrate how a conserved mechanism driving cell cycle entry has been adapted evolutionarily to connect auxin signaling with control of processes determining plant architecture.
Plant-parasitic cyst nematodes secrete CLAVATA3 (CLV3)/ESR (CLE)-like effector proteins. These proteins have been shown to act as ligand mimics of plant CLE peptides and are required for successful nematode infection; however, the receptors for nematode CLE-like peptides have not been identified. Here we demonstrate that CLV2 and CORYNE (CRN), members of the receptor kinase family, are required for nematode CLE signaling. Exogenous peptide assays and overexpression of nematode CLEs in Arabidopsis demonstrated that CLV2 and CRN are required for perception of nematode CLEs. In addition, promoter-reporter assays showed that both receptors are expressed in nematode-induced syncytia. Lastly, infection assays with receptor mutants revealed a decrease in both nematode infection and syncytium size. Taken together, our results indicate that perception of nematode CLEs by CLV2 and CRN is not only required for successful nematode infection but is also involved in the formation and/or maintenance of nematode-induced syncytia.
The shoot apical meristem (SAM) is the fundamental structure that is located at the growing tip and gives rise to all aerial parts of plant tissues and organs, such as leaves, stems and flowers. In Arabidopsis thaliana, the CLAVATA3 (CLV3) pathway regulates the stem cell pool in the SAM, in which a small peptide ligand derived from CLV3 is perceived by two major receptor complexes, CLV1 and CLV2-CORYNE (CRN)/SUPPRESSOR OF LLP1 2 (SOL2), to restrict WUSCHEL (WUS) expression. In this study, we used the functional, synthetic CLV3 peptide (MCLV3) to isolate CLV3-insensitive mutants and revealed that a receptor-like kinase, RECEPTOR-LIKE PROTEIN KINASE 2 (RPK2), also known as TOADSTOOL 2 (TOAD2), is another key regulator of meristem maintenance. Mutations in the RPK2 gene result in stem cell expansion and increased number of floral organs, as seen in the other clv mutants. These phenotypes are additive with both clv1 and clv2 mutations. Moreover, our biochemical analyses using Nicotiana benthamiana revealed that RPK2 forms homo-oligomers but does not associate with CLV1 or CLV2. These genetic and biochemical findings suggest that three major receptor complexes, RPK2 homomers, CLV1 homomers and CLV2-CRN/SOL2 heteromers, are likely to mediate three signalling pathways, mainly in parallel but with potential crosstalk, to regulate the SAM homeostasis.
Gene expression can be analyzed at high spatial resolution via RNA in situ detection methods. For many tissues and species, these will be performed on sections of embedded and fixed plant material. When very small or fragile tissues, such as embryos or roots are being investigated, whole mount methods can be employed. Protocols for both approaches are described in detail.
The plant hormone auxin plays a role in virtually every aspect of plant growth and development. Temporal and spatial distribution of auxin largely depends on the dynamic expression and subcellular localization of the PIN auxin-efflux carrier proteins. We show here that the Arabidopsis thaliana JAGGED LATERAL ORGAN (JLO) gene, a member of the LATERAL ORGAN BOUNDARY DOMAIN (LBD) gene family, is required for coordinated cell division during embryogenesis. JLO promotes expression of several PINFORMED (PIN) genes during embryonic and root development. Inducible JLO misexpression reveals that JLO activity is sufficient for rapid and high level PIN1 and PIN3 transcription. Genes of the PLETHORA (PLT) family respond to auxin and direct PIN expression, but PLT genes were severely underexpressed in jlo mutants. JLO controls embryonic patterning together with the auxin dependent MONOPTEROS/BODENLOS pathway, but is itself only mildly auxin inducible. We further show that all known auxin responses in the root require JLO activity. We thereby identify JLO as a central regulator of auxin distribution and signaling throughout plant development.
Revascularisation with Titanium-Nitride-Oxide (TiNOX) coated stents is safe and effective in patients with de novo native coronary artery lesions. In the TiNOX trial there was a reduction in restenosis and major adverse cardiac events as compared with stainless steel stents of otherwise identical design. The purpose of the present study was to evaluate the long-term outcome of these patients over five years.
Plants maintain stem cells in their meristems as a source for new undifferentiated cells throughout their life. Meristems are small groups of cells that provide the microenvironment that allows stem cells to prosper. Homeostasis of a stem cell domain within a growing meristem is achieved by signalling between stem cells and surrounding cells. We have here simulated the origin and maintenance of a defined stem cell domain at the tip of Arabidopsis shoot meristems, based on the assumption that meristems are self-organizing systems. The model comprises two coupled feedback regulated genetic systems that control stem cell behaviour. Using a minimal set of spatial parameters, the mathematical model allows to predict the generation, shape and size of the stem cell domain, and the underlying organizing centre. We use the model to explore the parameter space that allows stem cell maintenance, and to simulate the consequences of mutations, gene misexpression and cell ablations.
Stem cell number in shoot and floral meristems of Arabidopsis (Arabidopsis thaliana) is regulated by the CLAVATA3 (CLV3) signaling pathway. Perception of the CLV3 peptide requires the receptor kinase CLV1, the receptor-like protein CLV2, and the kinase CORYNE (CRN). Genetic analysis suggested that CLV2 and CRN act together and in parallel with CLV1. We studied the intracellular localization of receptor fusions with fluorescent protein tags and their capacities for interaction via efficiency of fluorescence resonance energy transfer. We found that CLV2 and CRN require each other for export from the endoplasmic reticulum and localization to the plasma membrane (PM). CRN readily forms homomers and interacts with CLV2 through the transmembrane domain and adjacent juxtamembrane sequences. CLV1 forms homomers independently of CLV2 and CRN at the PM. We propose that the CLV3 signal is perceived by a tetrameric CLV2/CRN complex and a CLV1 homodimer that localize to the PM and can interact via CRN.
Primary plant meristems are the shoot and root meristems that are initiated at opposite poles of the plant embryo. They contain stem cells, which remain undifferentiated, and supply new cells for growth and the formation of tissues. The maintenance of a long-lasting stem cell population in meristems is achieved by signal exchange between organizing regions and the stem cells, and also by feedback signals emanating from differentiating cells. Related peptide signals that make use of different receptor classes were found to control the stem cell populations in both meristem types by regulating evolutionarily conserved homeodomain transcription factors. The precise interplay of auxin and cytokinin signaling pathways is central to keep cells in the meristem, or direct them toward differentiation.
A tight but also dynamic regulation is necessary to control the size of stem cell populations in response to internal and external cues. The stem cells of the Arabidopsis shoot and root meristems are governed by the niche cells of the organizing centre (OC) and the quiescent centre (QC), respectively. The well characterized CLV3/WUS negative feedback loop adjusts homeostasis of the stem cell population in the shoot. Here, the CLAVATA3 (CLV3) dodecapeptide, expressed by the stem cells, signals to repress WUSCHEL (WUS), which is expressed in the subjacent OC cells, and in turn activates CLV3 expression non-cell autonomously. However, a similar signaling module controlling the root stem cell population was as yet unknown. In the June issue of Current Biology we report on such a signaling module comprising CLE40 (a CLV3 homologue) that acts via the receptor kinase Arabidopsis Crinkly4 (ACR4) to repress the WUS homologue WOX5 which maintains distal root stem cells. Furthermore, we showed that CLE40 peptide (CLE40p) treatment upregulates ACR4 expression. In this Addendum, we are further elaborating our hypothesis in which the upregulation of ACR4 as a consequence of ectopic CLE40p builds a protective barrier for the QC niche cells.
The plant shoot meristem maintains a group of stem cells that remain active throughout the plant life. They continuously generate new cells that are then recruited for organ initiation in the peripheral zone. Stem cell proliferation and daughter cell differentiation has to be integrated with overall growth and development of the diverse functional domains within the shoot apex. Several studies have revealed extensive communication between these domains. The signaling mechanisms employed comprise diffusible peptides, directional transport of plant hormones, but also complex interactions between transcription factors, that together establish a panoply of regulatory inputs that fine-tune stem cell behavior in the shoot meristem.
The niches of the Arabidopsis shoot and root meristems, the organizing center (OC) and the quiescent center (QC), orchestrate the fine balance of stem cell maintenance and the provision of differentiating descendants. They express the functionally related homeobox genes WUSCHEL (WUS) and WOX5, respectively, that promote stem cell fate in adjacent cells. Shoot stem cells signal back to the OC by secreting the CLAVATA3 (CLV3) dodecapeptide, which represses WUS expression. However, the signals controlling homeostasis of the root stem cell system are not identified to date. Here we show that the differentiating descendants of distal root stem cells express CLE40, a peptide closely related to CLV3. Reducing CLE40 levels delays differentiation and allows stem cell proliferation. Conversely, increased CLE40 levels drastically alter the expression domain of WOX5 and promote stem cell differentiation. We report that the receptor kinase ACR4, previously shown to control cell proliferation, is an essential component, and also a target, of CLE40 signaling. Our results reveal how, in contrast to the shoot system, signals originating from differentiated cells, but not the stem cells, determine the size and position of the root niche.
Multiparameter Fluorescence Image Spectroscopy (MFIS) is used to monitor simultaneously a variety of fluorescence parameters in confocal fluorescence microscopy. As the photons are registered one by one, MFIS allows for fully parallel recording of Fluorescence Correlation/Cross Correlation Spectroscopy (FCS/FCCS), fluorescence lifetime and pixel/image information over time periods of hours with picosecond accuracy. The analysis of the pixel fluorescence information in higher-dimensional histograms maximizes the selectivity of fluorescence microscopic methods. Moreover it facilitates a statistically-relevant data analysis of the pixel information which makes an efficient detection of heterogeneities possible. The reliability of MFIS has been demonstrated for molecular interaction studies in different complex environments: (I) detecting the heterogeneity of diffusion properties of the dye Rhodamine 110 in a sepharose bead, (II) Förster Resonance Energy Transfer (FRET) studies in mammalian HEK293 cells, and (III) FRET study of the homodimerisation of the transcription factor BIM1 in plant cells. The multidimensional analysis of correlated changes of several parameters measured by FRET, FCS, fluorescence lifetime and anisotropy increases the robustness of the analysis significantly. The economic use of photon information allows one to keep the expression levels of fluorescent protein-fusion proteins as low as possible (down to the single-molecule level).
Organ initiation requires the specification of a group of founder cells at the flanks of the shoot apical meristem and the creation of a functional boundary that separates the incipient primordia from the remainder of the meristem. Organ development is closely linked to the downregulation of class I KNOTTED1 LIKE HOMEOBOX (KNOX) genes and accumulation of auxin at sites of primordia initiation. Here, we show that Arabidopsis thaliana JAGGED LATERAL ORGANS (JLO), a member of the LATERAL ORGAN BOUNDARY DOMAIN (LBD) gene family, is required for coordinated organ development in shoot and floral meristems. Loss of JLO function results in ectopic expression of the KNOX genes SHOOT MERISTEMLESS and BREVIPEDICELLUS (BP), indicating that JLO acts to restrict KNOX expression. JLO acts in a trimeric protein complex with ASYMMETRIC LEAVES2 (AS2), another LBD protein, and AS1 to suppress BP expression in lateral organs. In addition to its role in KNOX regulation, we identified a role for AS2 in regulating PINFORMED (PIN) expression and auxin transport from embryogenesis onwards together with JLO. We propose that different JLO and AS2 protein complexes, possibly also comprising other LBD proteins, coordinate auxin distribution and meristem function through the regulation of KNOX and PIN expression during Arabidopsis development.
Global climate change and a growing population require tackling the reduction in arable land and improving biomass production and seed yield per area under varying conditions. One of these conditions is suboptimal water availability. Here, we review some of the classical approaches to dealing with plant response to drought stress and we evaluate how research on RECEPTOR-LIKE KINASES (RLKs) can contribute to improving plant performance under drought stress. RLKs are considered as key regulators of plant architecture and growth behavior, but they also function in defense and stress responses. The available literature and analyses of available transcript profiling data indeed suggest that RLKs can play an important role in optimizing plant responses to drought stress. In addition, RLK pathways are ideal targets for nontransgenic approaches, such as synthetic molecules, providing a novel strategy to manipulate their activity and supporting translational studies from model species, such as Arabidopsis thaliana, to economically useful crops.
The growth of a plants root system depends on the continued activity of the root meristem, and the generation of new meristems when lateral roots are initiated. Plants have developed intricate signalling systems that employ secreted peptides and plasma membrane-localized receptor kinases for short- and long-range communication. Studies on growth of the vascular system, the generation of lateral roots, the control of cell differentiation in the root meristem and the interaction with invading pathogens or symbionts has unravelled a network of peptides and receptor systems with occasionally shared functions. A common theme is the employment of conserved modules, consisting of a short signalling peptide, a receptor-like kinase and a target transcription factor, that control the fate and proliferation of stem cells during root development. This review intends to give an overview of the recent advances in receptor and peptide ligand-mediated signalling involved in root development.
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