Plant & Animal Genomes XIV Conference

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

Genome Organization Of Nodule-Related Genes And Their Expression Profiling

Jing Yi , 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

Nitrogen-fixing nodules that result from the symbiotic relationship between rhizobial bacteria and legume roots require expression of both plant and microbial genes. Although many of the plant genes involved in the nodule formation have been identified, with the sequence of a majority of the Medicago truncatula genome available, we now have investigated their genomic organization by comparing the known nodule-related genes with the genomic sequence. These studies revealed that although most of the nodule-specific genes are dispersed on different chromosomes, several of them do occur in clusters. For example, five genes similar to the soybean nodulin-26 gene are clustered within 23 Kb on chromosome 2 and a Ka/Ks analysis reveals that they are under purifying selection. To better understand the expression of these genes under a variety of conditions, the expression profiles of nodule-related genes involved in the early stage of the nodule formation were compared by analysis of the publicly available EST data. This analysis show that, in addition to partial involvement in micorrhizal signaling pathway, homologs of NFR5, NFR1, NORK, SYMRK, DMI1, DMI2, DMI3, NSP1 and NSP2 genes that function in the nod factor signal pathway, also are expressed during drought and/or abiotic stress. In addition, the Medicago truncatula nodulin MTN5 gene also was expressed in phosphate-starved leaf, pathogen-infected root and drought plantlets. These observations indicate that many of the genes expressed in the early stage of nodulation also may play a role in how in the plant responds to stressed conditions.