Broadening host specificity in soybean-Rhizobia symbiosis

Fixed nitrogen derived from symbiotic relationships with bacteria (rhizobia) is essential for soybean growth and seed set. However, soybean-rhizobia associations are highly specific, and most rhizobial strains can only establish symbiotic relationships with specific cultivars. Based on a targeted screen we identified three candidate genes, which when silenced improve soybean ability to be nodulated by incompatible strains of Rhizobacteria. We propose to extend this work further by generating stable transgenic soybean lines that are silenced for each of the identified genes and to test the efficacy on nodulation by incompatible rhizobacteria in the field. We also propose to test the effect of silencing target genes on soybean associations with other beneficial organisms including mycorrhizal fungi. Improved nodulation is expected to the nitrogen fixing ability of plants, which in turn will reduce production costs by lowering the need for fertilizer applications. If alteration of gene expression enhances interaction with beneficial fungi, additional advantages to soybean production are expected. These include improved tolerance to biotic and abiotic stresses. Specifically the following benefits are predicted: a) Improve soybean productivity by increasing nitrogen fixation efficiency b) Lower production costs by reducing the need for fertilizer applications c) Benefit the environment by reducing the need for fertilizer applications d) Improve soybean production by increasing soybean tolerance to abiotic stresses including drought and heat tolerance e) The outcome of these studies and appropriate recommendations will be communicated to growers at meetings, field days, newsletter articles, and posted on University internet resources including the Department of Plant Pathology web site: http://www.ca.uky.edu/agcollege/plantpathology/extension/index.html