Research Accomplishment Reports 2007

Dissecting Soybean Defense Pathways Using Virus-induced Gene Silencing

A. Kachroo, S.A. Ghabrial
Department of Plant Pathology

 

Project Description

This project has only recently been intiated. Based on previous work on Arabidopsis, which has established a role for fatty acids in plant defense, a soybean desaturase gene involved in the biosynthesis of unsaturated fatty acids was targeted for silencing. Successful silencing of this gene results in distinct morphological phenotypes, including severe growth abnormalities and reduced chlorophyll content. Fatty acid analysis indicates that the desaturase-silenced plants accumulate increased amounts of stearic acid, the preferred substrate for the desaturase protein and reduction in the product (oleic acid).

These plants also appear to be upregulated in pathogenesis-related gene expression. Assessment of bean pod mottle virus (BPMV) accumulation in the silenced plants showed significant increases in virion accumulation, suggesting that silencing of the desaturase gene enhanced plant susceptibility to BPMV infection and implied a role for the desaturase gene in host defense. We are currently analyzing these plants for their lipid content, seed yield, fatty acid composition of seed oil, and other phenotypes.

We have also identified soybean orthologs of some key components of defense signaling pathways mediated by the plant hormones salicylic acid (SA) and, jasmonic acid (JA), as well components required for resistance (R) gene-mediated defense. Orthologous sequences were identified from the soybean expressed sequence tag (EST) database, based on similarities to proteins from Arabidopsis thaliana and tobacco. These sequences will be used to silence the endogenous genes, and their roles in soybean defense against soybean mosaic virus and Phytophthora sojae, will be examined.

Impact

Part of protecting our food supply involves boosting plant defenses against microbial invaders. We plan to identify and characterize key molecules involved in soybean resistance against viral and fungal pathogens. This will be achieved based upon existing information from well-studied model plants, and using our unique gene-silencing tool for functional studies in soybean. A basic understanding of the plant's own defense mechanisms would potentially provide the soybean research community with a means to generate a more robust soybean crop without employing costly chemicals or generating transgenic crops.