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Dissecting Soybean Defense Pathways Using Virus-induced Gene Silencing
Kachroo, A., S. A. Ghabrial
Department of Plant Pathology
Soybean is the world's largest legume crop and a major source of edible plant oils and proteins. Despite the economic importance of this crop and the devastating losses incurred by its diseases, very little is known about the molecular mechanisms underlying soybean defense against its pathogens. Elucidation of signal transduction pathway(s) downstream of the initial pathogen recognition event would aid in the engineering of novel, enduring, and broad-spectrum disease resistance.
Although a large number of resources and genomic tools are available for soybean, studies related to gene functions have been lacking due to the unavailability of rapid functional genomics tools for soybean. A novel virus based gene-silencing system recently developed in the Co-PIs' laboratory will used along with existing information on defense signaling in the model plant Arabidopsis to assign defense-related functionality to various soybean genes.
Specifically this proposal aims to identify the molecular components responsible for mediating defense against two major pathogens of soybean, Phytophthora sojae and soybean mosaic virus. It is anticipated that this work will have a significant impact on advancing the limited understanding of how soybean protects itself from microbial pathogens. Functional genomics research in soybean could potentially lead to the generation of new varieties with improved nutritional and agronomic characteristics.
2009 Project Description
Research pertaining to objectives 1a, 1c and 2 was conducted. Results obtained have improved our understanding of resistance gene-mediated signaling and the roles of defense-related phytohormones in soybean defense to microbial pathogens. These research findings were presented as two-oral and four-poster presentations at annual society (International Society of Molecular Plant-Microbe Interactions, American Phytopathological Society, American Society of Plant Biologists, American Society for Virology) conferences (2009). The project has resulted in the training of four undergraduate, one high school and two graduate students and two postdoctoral researchers.
Research related to this project identified the following:
i) Low oleic acid-mediated defense signaling pathway is conserved in soybean. Reduction of oleic acid induces multiple defense responses in soybean including, increased expression of pathogenesis-related genes, accumulation of salicylic acid and enhanced basal resistance to Pseudomonas syringae and Phytophthora sojae.
ii) Exogenous glycerol application can mimic the effects of reduction in oleic acid levels to induce broad-spectrum and long-lasting resistance to multiple pathogens in soybean. This approach is being developed further for potential improvement of soybean productivity.
iii) Identified GmRAR1 and GmSGT1-2 as components of resistance gene-mediated signaling in soybean defense against P. syringae and soybean mosaic virus. Functional analysis of genes encoding these proteins has shown that GmRAR1 and GmSGT1-2 modulate basal, effector-triggered and systemic immunity in soybean.
iv) Examined the roles of the phytohormones salicylic acid and jasmonic acid in mediating soybean defense to various pathogens. These studies are being prepared for publication in a peer-reviewed journal.
Kachroo A, Kachroo P. (2009) Fatty acid derived signals in plant defense. Annual Review of Phytopathology 47:153-176
Kachroo A, Ghabrial SA (2009) Virus-induced gene silencing in soybean. In Methods in Molecular Biology. Ed. J.M. Walker. Humana Press Inc. (in press)