New pathways regulating Medicago truncatula root architecture

O FRUGIER F, PLET J, ARIEL F, BOUALEM A, LAFFONT C, LAPORTE P, JOVANOVIC M, NAYA L, CHAN R, SALLET E, GOUZY J, HARTMANN C, LELANDAIS C AND CRESPI M

Gant, Bélgica

Conferencia; 8th European Nitrogen Fixation Conference; 2008

Ghent University

Legumes are characterized by their ability to develop two lateral organs from primary roots depending on environmental conditions, lateral roots (common to all plants) and nitrogen-fixing nodules. Physiological and genetic data indicate that development of these organs is coordinated and involves common regulatory pathways, including phytohormonal controls.   Recently, cytokinin signalling mediated by the receptor MtCRE1 has been identified as crucial for both organogeneses in the Medicago truncatula model legume (1). We characterized symbiotic and non-symbiotic root phenotypes of M. truncatula mutants affected in cytokinin signalling genes, obtained through the TILLING platform developed in the frame of the Grain Legumes EEC project (GLIP; C. LeSignor and R. Thompson, INRA-Dijon; D. Baker and J. Clarke, JIC-Norwich). This coupled with transcriptomic approaches allowed us the identification of new cross-talk elements between nodulation and cytokinin signalling pathways. Regulation of transcript stability mediated by microRNAs has been associated to various plant developmental processes. We notably showed that MtmiR166 regulation, which targets type III HD ZIP transcription factors, is crucial for patterning of root vascular bundles, and formation of both lateral roots and nodules. Parallel analysis of small RNA libraries from M. truncatula roots and nodules is being done to extend our knowledge on the role of miRNA-mediated riboregulation in symbiotic interactions.  Altogether, we characterized several new pathways integrating symbiotic and non-symbiotic root architectures in legumes.   (1) Gonzalez-Rizzo S., Crespi M. and Frugier F. The Medicago truncatula CRE1 cytokinin receptor regulates lateral root development and early symbiotic interaction with Sinorhizobium meliloti. (2006) Plant Cell 18, 2680-2693.