IDENTIFICATION OF NOVEL LEGUME-SPECIFIC GENE FAMILIES: A POTENTIAL SOURCE OF NEW TARGETS FOR CROP IMPROVEMENT

¹ Department of Plant Biology, University of Minnesota, 250 Biological Sciences Center, 1445 Gortner Avenue, St. Paul MN 55108

Legumes have enormous agronomic importance. They are a major commercial source of protein, oils, forage, and phytochemicals important for human health. Additionally, they are able to fix nitrogen with symbiotic bacteria, improving the soils in which they are grown. A first step toward selecting candidate genes for crop improvement is to identify genes that are both unique to legumes, and specifically expressed in desired tissues. To carry out this first step, we have performed a systematic analysis of the expressed sequence tags (ESTs) for three legumes: Medicago truncatula, Glycine max/soja, and Lotus japonicus. These sequences were compared to all publicly available non-legume sequences by a variety of BLAST algorithms. Legume sequences with no similarity to non-legumes were clustered into homologous groups of related sequences. Among these final legume-specific families of sequences, there are ten separate groups specific to roots and nodules, eight specific to seeds, four appearing only in leaves and flowers, and seven in stressed or pathogen inoculated tissues. Many of these families contain genes that are heavily expressed, and none of the tissue-specific sequences have a known function. However, our analysis of sequence motifs shared within each group suggests potential roles for defense, self-incompatibility, and other possible targets for crop improvement. In the future, we will attempt to verify functional hypotheses for selected candidates via full-length sequencing, RNAi mediated gene silencing, and directed biochemical assays.