CS-15-5 - Insights into the Autoregulation of Nodulation (AON) Pathway Gained by Transcriptomics of the Maturation Zone of M. Truncatula Wild Type and Mutant Plant Roots in the First 3 Days Post Inoculation with Rhizobia
Alumni Distinguished Professor of genetics Clemson University
The complex molecular signaling that underlies the ability of legumes to host rhizobia and benefit from nitrogen fixation by the bacteria is a topic of intense study. The converse process, the need of the legume plant to regulate the number of rhizobia that colonize the roots or to eliminate colonization altogether when adequate nitrate is available in the soil (AON) also requires complex signaling. Split root experiments have determined that AON in Medicago truncatula occurs by 48-72 hours after inoculation with rhizobia; in effect both development of rhizobial colonization and limitation of further colonization are occurring at the same time in the same cells. In order to understand the nature of this signaling, we performed RNASeq on libraries derived from the zone of developing nodules and compared the results with libraries made from comparable tissue derived from uninoculated roots at 0, 12, 24, 48, and 72 hours post inoculation. We also sequenced libraries made from sunn and rdn1 hypernodulation mutants as well as shoots of plants following the same time course. Examination of differentially expressed genes at various time points and identification of modules of genes that are co-regulated across time points in both the wild type and the mutants has allowed us to begin to unravel the complex molecular signaling behind AON. Comparison of wild type and hypernodulation mutants revealed known nodulation genes that are differentially regulated in the mutants versus wild type undergoing nodulation, as well as novel genes with coordinate regulation that differs between mutants and wild type, suggesting underlying mechanisms for the phenotypes observed. This work is supported by NSF IOS#1444461 to Frugoli and Feltus.