Little is known about identities of the large number of genes involved in resistance to stresses in soybeans. This constitutes a major limitation to future enhancement of soybean yield and seed quality. Significant progress strongly suggests that the research reported here is successful. It has identified soybean genes involved in stress resistance pathways and results are expected to add to this knowledge and expand it to other diseases. The data from this project are adding to the understanding of plant defense networks to allow improvement in resistance to biotic and abiotic stress, reduce stress-related yield loss, and enable best management practices for soybean producers.
The VIGS technology utilized in this project uses bean pod mottle virus (BPMV) to carry (vector) pieces of soybean gene sequences into the plant to turn off (silence) requisite target genes. In this technology, a piece of a soybean gene identified as potentially interesting is inserted into the BPMV virus vector. When this BPMV virus vector is used to infect a soybean plant, it carries a piece of the soybean gene along with it. Soybean plants defend themselves against viruses by attempting to degrade the RNA of the virus. Therefore, as the soybean plant attempts to defend itself against BPMV, it also degrades the RNA identical to that of the gene that has been incorporated into the virus. The degraded soybean gene is no longer functional and thus, creates a mutant soybean plant that has lost the function of that particular gene. Thus, VIGS allows for rapid screening and observation of the plant characteristics to assess the impact and function of the gene under study. The vector can be introduced into plants through simple mechanical (rubbing) inoculation and it allows us to modulate BPMV symptom severity to provide the opportunity to optimize assay conditions.
To date, we have developed a library of VIGS constructs targeting over 800 soybean genes. These constructs are being distributed to our collaborators for use in several studies. Through working with the SoyBase curators, the VIGS information is publicly available at http://www/soybase.org/SoyVIGS/. Data include clone names, target genes, target sequences, primer sequences, creator, phenotype descriptions, and images of assay plants.
Because of the success in the high throughput screening of multiple genes involved in stress resistance we believe a pattern is emerging that suggests that interactions between the stress-causing agents and the soybean are complex and dynamic. Proteins encoded or secreted by a microbe interact with recognition receptors or proteins of the soybean plant to result in either disease (stress) or resistance. It has become increasingly evident that this interactive network or “interactome” can be revealed through data obtained as a result of VIGS. Thus, results from our experiments may be more far-reaching than earlier believed. The process of revealing the organization of the “interactome” which converges into “hubs” will provide the opportunity to control key targets that can be manipulated by either silencing or over expression to confer resistance to each of the diseases (as well as others) under investigation in this project. Patterns emanating from work with Asian soybean rust and Soybean mosaic virus may allow opportunity to identify/control key targets (marker assisted selection) for manipulating resistance to stress.
The project now encompasses 13 labs at 5 locations (in addition to labs working independently through use of the VIGS system obtained under MTAs) that are using VIGS to identify soybean genes involved in defense. We believe the compiled data will impart clarity to the understanding of soybean defense networks and the genes that are the key players in activating the network to produce a more resistant soybean.