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 are currently generating stable transgenic soybean lines that are downregulated for two of the identified genes. Once stable transgenics are confirmed, we will test their responses to nodulation by incompatible rhizobacterial strains in the green house and under field conditions. We also propose to test the response of the three silenced lines to other incompatible rhizobacterial strains and efficacy of nodulation under conditions of abiotic stresses that are known to affect nodulation efficiency in the field. 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