Cloning and characterization of a soybean SNF2 yeast homolog

It is of great economic and scientific interest to understand plant disease resistance genes at the molecular level. Phytophthora sojae, a fungal pathogen of soybean is of particular interest since the root and stem rot resulting from its infection causes great economic loss. It is the goal of this project to clone Phytophthora resistance genes from soybean. This was done by designing primers from the conserved regions of known plant disease resistance genes using a modified differential display for near isogenic lines; L85-3044 a resistant line and Williams, a susceptible line. Several polymorphic bands were identified, including a unique 0.7 kb band. This DNA fragment was cloned and used to screen libraries. To accomplish this, genomic and cDNA libraries of L85-3044 were constructed. Several interested clones have been identified. One of the positive cDNA clones was identified as gmSNF2 that was a yeast SNF2 gene homolog. The putative gmSNF2 protein has, a leucine zipper motif, an ATP binding motif and a leucine content of 11%. It also has a 39.0% similarity to six known plant disease resistance genes. Genetic complementation test of yeast SNF2 mutant indicate that soybean gmSNF2 gene has SNF2 function in yeast. The SNF2 gene of yeast is a member of a large group of related proteins that exhibit a broad range of biological functions, such as gene-specific transcriptional activation, and transcriptional repression. To determine if the gmSNF2 would restore pathogen resistance to susceptible lines, the putative resistance genes were introduced into the roots of soybean by Agrobacterium rhizogenes mediated transformation. A protocol for screening Phytophthora sojae resistance in transgenic roots was also developed based on color assay and thin layer chromatography. The analysis of transgenic susceptible varieties Williams and Hark showed that gmSNF2 could produce significant resistance-reactions. We thus hypothesize that the gmSNF2 gene may sense the free sugar molecular released from fungal wall by soybean glucanases and initiate a sugar mediate signal transduction pathway for Phytophthora sojae resistance.