Plant & Animal Genomes XIII Conference

January 15-19, 2005
Town & Country Convention Center
San Diego, CA

The NIP And SLI Genes Of Medicago truncatula Are Required For Normal Rhizobial Invasion Of The Symbiotic Root Nodule

Harita Veereshlingam¹ , Janine G. Haynes² , D. Janine Sherrier² , Rebecca Dickstein¹

¹  Department of Biological Sciences, University of North Texas, Denton, TX 76203 USA

²  University of Delaware, Delaware Biotechnology Institute, Newark, DE 19711 USA

In response to compatible rhizobia, leguminous plants develop unique plant organs, root nodules, in which rhizobia fix nitrogen into ammonia. During nodule invasion, the rhizobia gain access to newly divided cells, the nodule primordia, in the root inner cortex through plant-derived cellulose tubes called infection threads. Infection threads begin in curled root hairs and bring rhizobia into the root crossing several cell layers in the process. Ultimately the rhizobia are deposited within nodule primordium cells through a process resembling endocytosis. Plant host mechanisms underlying the formation and regulation of the invasion process are not understood. To identify and clone plant genes required for nodule invasion, recent efforts have focused on Medicago truncatula. From an EMS-mutagenized population of M. truncatula, we identified two non-allelic mutants, nip (numerous infections with polyphenolics; Veereshlingam et al. Plant Physiology, In Press) and sli (sluggish infections) with defects in nodule invasion. Infection threads were found to proliferate abnormally in the nip mutant nodules with only very rare deposition of rhizobia within plant host cells. nip nodules were found to accumulate polyphenolic compounds, indicative of a host defense response. Interestingly, nip was also found to have defective lateral root elongation suggesting that NIP has a role in both nodule and lateral root development. NIP was found to map at ~ 0 cM on chr. 1 and efforts to clone NIP by a map-based approach are ongoing. In sli, infection threads were observed to bring rhizobia from infection threads to newly divided nodule primordium cells in the roots inner cortex. Polyphenolic accumulation in sli nodule/bumps was found. Efforts to map SLI onto the M. truncatula genetic map are ongoing and future efforts will be directed towards map-based cloning of SLI. Supported by UNT Faculty Research Program.