Soybean Functional Genomics: Gene Discovery Through Fast Neutron Mutagenesis

Soybean is a major plant source of protein and oil, can fix atmospheric nitrogen and produces important secondary metabolites beneficial for human health.  The published  whole-genome soybean sequence (Schmutz et al., 2010) predicts more than 46,000 protein coding genes. A major future challenge will be assigning function to each of these genes, or at least identifying critical genes necessary for agronomic improvement. We developed a large collection of deletion mutants in the soybean cultivar Williams 82 through fast neutron (FN) mutagenesis. Our goal is to develop an efficient resource for the investigation of soybean gene function through forward and reverse genetics. Unlike transposon-tagged mutants, deletion mutants (e.g., induced by fast neutron irradiation) are not widely utilized in gene function studies because mutated genes are often difficult to identify.  However, the use of whole-genome, array-based oligonucleotide comparative genome hybridization (CGH) allowed us to rapidly identify candidate genes for a number of the mutants. For example, using CGH, we were able to confirm the published deletion of FAD2-1A in M23, an X-ray mutant used for breeding for increased oleic acid content in soybean (Bolon et al., 2011). Thus far, we have isolated a number of mutants that are affected in growth and development, transitory starch accumulation and key seed traits. CGH analysis of selected FN mutants indicated that FN irradiation causes deletions ranging from one gene model to >3.0 Mb. The potential use of FN mutagenesis in soybean gene discovery, as well as in identifying mutant lines with agronomic relevance, will be discussed.