Plants within the Orobanchaceae are an agriculturally important group of parasites that attack economically important crops to obtain water and nutrients from their hosts. Despite their agricultural importance, molecular mechanisms of the parasitism are poorly understood.
Horizontal gene transfer has been postulated to occur between crops to co-occurring parasitic plants, but empirical evidence has been lacking. We present evidence that an HGT event moved a nuclear monocot gene into the genome of the eudicot parasite witchweed (Striga hermonthica), which infects many grass species in Africa. Analysis of expressed sequence tags revealed that the genome of S. hermonthica contains a nuclear gene that is widely conserved among grass species but is not found in other eudicots. Phylogenetically, this gene clusters with sorghum genes, the monocot host of the parasitic weed, suggesting that nuclear genes can be captured by parasitic weeds in nature.
The obligate parasitic plant witchweed (Striga hermonthica) infects major cereal crops such as sorghum, maize, and millet, and is the most devastating weed pest in Africa. An understanding of the nature of its parasitism would contribute to the development of more sophisticated management methods. However, the molecular and genomic resources currently available for the study of S. hermonthica are limited.
Recently, endoscopic ultrasonography-guided fine needle aspiration (EUS-FNA) has been applied for diagnosis of gastrointestinal submucosal tumors. There have been no definite criteria, however, for the adequate cytological diagnosis of gastrointestinal stromal tumor (GIST) in practice. To facilitate this a novel method is proposed that combines cytology and histology. For 49 cases of submucosal tumor of gastrointestinal tract, EUS-FNA was performed. The aspirated materials were processed for cytology and histology. Both cytological and histological findings were examined on immunocytochemical and immunohistochemical staining of c-kit. Of 49 cases, 40 (81.6%) proved adequate for cytological and/or histological examination. On cytology, cluster types were classified into type A (piled clusters with high cellularity showing a fascicular pattern), type B (thin layered clusters with high cellularity showing a fascicular pattern), and type C (mono-layered clusters or scattered cells). Types A and B were strongly associated with histological diagnosis of GIST. Type C clusters needed confirmation on c-kit positivity and histology. Thus, the combined cytology with newly defined features, and classification and histological diagnostic method for EUS-FNA materials can contribute to improved routine diagnosis for GIST.
* Witchweeds (Striga spp.) are major agricultural pests that infest important crops in sub-Saharan Africa. Striga hermonthica parasitizes gramineous plants including sorghum, maize and rice, but not dicots. To understand host recognition mechanisms of S. hermonthica, we investigated its interaction with nonhost dicots including Arabidopsis, cowpea, Lotus japonicus and Phtheirospermum japonicum, a hemiparasite. * Striga hermonthica seeds were pretreated with strigol, a germination stimulant, and allowed to germinate next to a potential host root. We characterized the histological phenotype of the interactions. Moreover, we monitored the infection of a host rice and the nonhost P. japonicum by S. hermonthica using time-lapse photography. * All nonhost dicots tested did not support S. hermonthica shoot growth beyond the six leaf-pair stage; however, the arrest of parasite development occurred at different stages. Striga hermonthica haustoria were able to reach the steles of Arabidopsis and cowpea, while L. japonicus blocked S. hermonthica infection in the root cortex. Striga hermonthica often failed to penetrate P. japonicum roots. * Our analysis indicates that there are at least four types of incompatible interaction to S. hermonthica. Combinations of these different incompatibility mechanisms contribute to the total resistance to S. hermonthica.
Although it has been well documented that aberrant major histocompatibility complex class II molecules may contribute to the development of autoimmune disorders, the precise mechanisms responsible for their tissue-specific expression remain unknown. Here we show that estrogen deficiency induces aberrant class II major histocompatibility complex expression in exocrine glands via interactions between epithelial cells and plasmacytoid dendritic cells. Relatively modest but functionally significant expression levels of major histocompatibility complex class II and class II transactivator molecules were observed in the exocrine glands of ovariectomized (Ovx) C57BL/6 (B6) mice, but were not seen in the exocrine glands of control B6 mice. We observed that the salivary dendritic cells adjacent to the apoptotic epithelial cells positive for terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling, were activated in Ovx mice, but were not activated in control mice. We obtained evidence that the salivary gland cells express both interferon regulatory factor-1 and class II transactivator type IV molecules in Ovx mice. Salivary gland cells from Ovx mice were also capable of inducing the activation of antigen-specific T cells from OT-II transgenic mice. These findings indicate that estrogen deficiency initiates class II transactivator type IV mRNA expression in exocrine glands via interactions between epithelial cells and plasmacytoid dendritic cells, suggesting that plasmacytoid dendritic cells play a pivotal role in gender-based autoimmune disorders in postmenopausal women.
Arbuscular mycorrhiza (AM) represents an ancient endosymbiosis between plant roots and Glomeromycota fungi. Strigolactones (SLs), plant-derived terpenoid lactones, activate hyphal branching of AM fungi before physical contact. Lack of SL biosynthesis results in lower colonization of AM fungi. The F-box protein, DWARF3 (D3), and the hydrolase family protein DWARF14 (D14) are crucial for SL responses in rice. Here we conducted AM fungal colonization assays with the SL-insensitive d3 and d14 mutants. The d3 mutant exhibited strong defects in AM fungal colonization, whereas the d14 mutant showed higher AM fungal colonization. As D14 has a homologous protein, D14-LIKE, we generated D14-LIKE knockdown lines by RNA interference in the wildtype and d14 background. D14 and D14-LIKE double knockdown lines exhibited similar colonization rates as those of the d14-1 mutant. D3 is crucial for establishing AM symbiosis in rice, whereas D14 and D14-LIKE are not. Our results suggest distinct roles for these SL-related components in AM symbiosis.
Obligate parasitic plants in the family Orobanchaceae, such as Striga and Orobanche (including Phelipanche) spp., parasitize important crops and cause severe agricultural damage. Recent molecular studies have begun to reveal how these parasites have adapted to hosts in a parasitic lifecycle. The parasites detect nearby host roots and germinate by a mechanism that seems to have evolved from a conserved germination system found in non-parasites. The development of a specialized infecting organ called a haustorium is a unique feature of plant parasites and is triggered by host compounds and redox signals. Newly developed genomic and genetic resources will facilitate more rapid progress toward a molecular understanding of plant parasitism.
The Lotus japonicus SYMBIOSIS RECEPTOR-LIKE KINASE (SYMRK) is required for symbiotic signal transduction upon stimulation of root cells by microbial signaling molecules. Here, we identified members of the SEVEN IN ABSENTIA (SINA) E3 ubiquitin-ligase family as SYMRK interactors and confirmed their predicted ubiquitin-ligase activity. In Nicotiana benthamiana leaves, SYMRK-yellow fluorescent protein was localized at the plasma membrane, and interaction with SINAs, as determined by bimolecular fluorescence complementation, was observed in small punctae at the cytosolic interface of the plasma membrane. Moreover, fluorescence-tagged SINA4 partially colocalized with SYMRK and caused SYMRK relocalization as well as disappearance of SYMRK from the plasma membrane. Neither the localization nor the abundance of Nod-factor receptor1 was altered by the presence of SINA4. SINA4 was transcriptionally upregulated during root symbiosis, and rhizobia inoculated roots ectopically expressing SINA4 showed reduced SYMRK protein levels. In accordance with a negative regulatory role in symbiosis, infection thread development was impaired upon ectopic expression of SINA4. Our results implicate SINA4 E3 ubiquitin ligase in the turnover of SYMRK and provide a conceptual mechanism for its symbiosis-appropriate spatio-temporal containment.
It is desirable to increase the flavonoid contents of postharvest vegetables since flavonoids play a beneficial role in human health promotion. In the present study, we show that postharvest vegetables increasingly produced flavonoids when irradiated with light near the absorption wavelength of flavonoids in the plant. Three-day exposure to UV-B for 5 min, 98 ?mol m?² s?¹ per day, increased the contents of jaceidin in spinach, kaempherol glycoside in radish sprout, apigenin glycosides in parsley, and isovitexin in Indian spinach after 6 days of storage in a refrigerator, compared to the contents in plants without irradiation. Six days of storage of unripe green strawberry under green light for 5 min, 98 ?mol m?² s?¹ per day, enabled them to mature and turn red, accompanied by 3.5-fold increased contents of pelargonidin. Elucidation of the mechanism in parsley found the stimulating expression of the flavonoid synthesis gene, PAL, C4H, 4CL, CHS, and FNS, 6 h after exposure to single irradiation with UV-B for 5 min, and the higher expression was maintained for 24 h. After 3 days irradiation during 6 days of storage, parsley did not show adverse changes in the contents of ascorbic acid, ?-carotene, chlorophyll, and moisture.
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