Doctorate thesis of National Institute of Further Education in Agricultural Science

Friday, June 12, 2015


Ion channels of Medicago truncatula root hair and early electrical signaling of the nodulation: from the channel gene repertoire to functional analyzes

Alice Drain
BPMP, “Ion Channels” team


Jury :
M. Pascal RATET, DR CNRS, Gif-sur-Yvette, Rapporteur
M. Sébastien THOMINE, DR CNRS,Gif-sur-Yvette, Rapporteur
Mme Clare GOUGH, DR CNRS, Toulouse, Examinateur
M. Guillaume BÉCARD, Professeur UPS, Toulouse, Examinateur
M. Michel LEBRUN, Professeur UM, Montpellier, Examinateur
M. Hervé SENTENAC, DR INRA, Montpellier, Directeur de thèse


Abstract :
The legume-rhizobium symbiosis is of crucial importance in terrestrial ecosystems because it allows the plant to assimilate atmospheric nitrogen. The establishment of the interaction between plant root hairs and their symbiotic bacterial partners relies on complex signaling mechanisms. The earliest detected event, immediately triggered by root hair perception of Nod-factors, is a Ca2+ influx, proton pump inhibition and efflux of Cl- resulting in depolarization of the cell membrane. This depolarization is followed by K+ efflux, allowing repolarization of the cell membrane. The general objective of this work is to identify the molecular mechanisms underlying this electrical signaling by using the legume model Medicago truncatula. In a first step, we identified candidate ion channels and transporters by analyzing the root hair transcriptome obtained by RNA-Seq. Then, several candidate genes (1 member from the CNGC channel family, 1 from the Shaker K+ channel family and 2 from the SLAC anion channel family) were expressed in Xenopus oocytes to check their activity in this heterologous system and determine their functional properties. Then, we focused on the gene encoding the Shaker channel, shown to mediate outwardly-rectifying voltage-gated K+ selective currents. We analyzed its expression pattern using a GUS construct and its function in planta by phenotyping a loss-of-function mutant pant. A first set of experiments has shown that the loss-of-function mutation does not suppress the plant nodulation capacity but significantly depresses it. It also affects the control of stomatal aperture upon water stress but let unchanged K+ secretion into the xylem sap in roots and translocation towards the shoots.