Plant & Animal Genomes XIV Conference

January 14-18, 2006
Town & Country Convention Center
San Diego, CA

Expression Profile And Genomic Organization Of Regions Containing Clusters Of NBS-LRR Genes In Medicago truncatula

Shweta Deshpande , Fares Najar , Bruce A Roe

  Department of Chemistry and Biochemistry Stephenson Research and Technology Center The University of Oklahoma 101 David L. Boren Blvd. Norman, Oklahoma 73019

As a member of the international consortium sequencing the model legume, Medicago truncatula, our laboratory is sequencing chromosomes 1, 4, 6 and 8. With over 1566 BACs sequenced representing over half of the euchromatic region, we now have begun a genomic analysis focusing initially on the disease resistance genes with sequence homology to known NBS-LRR genes. For example; the NBS-LRR superfamily of plant resistance genes is the largest and most common of the disease resistance gene group. Mapping of the NBS-LRR containing BAC contigs and ESTs representing resistance genes now reveals that chromosomes 4 and 6 of Medicago truncatula contains most of the TIR type NBS-LRR disease resistance genes while a large portion of the non-TIR type map to chromosome 3,5 and 8. A preliminary blastp analysis of these NBS-LRR regions against the Medicago truncatula EST libraries reveals that these genes are expressed in the mixed tissue, seedling roots, immature pod walls and roots nodules. Furthermore when the genomic regions with clustered NBS-LRR genes were examined, we observed that each separate cluster encodes genes with its own unique resistance specificity, often with high levels of conservation in their encoded motifs but with significant divergence in their flanking sequences. Therefore a picture now is emerging that is consistent with the notion that duplication of disease resistant genes is a critical factor in broadening a meaningful plant response to various external stress related factors.