Doctorate thesis of Montpellier University
Tuesday, july 13, 2021
at 9 AM –Campus de La Gaillarde- BPMP library room without audience in videoconference.
Zoom link: https://cnrs.zoom.us/j/92041279524
ID de réunion : 920 4127 9524
Code secret : 1m8dQq
Doctorale school : GAIA – Biodiversité, Agriculture, Alimentation, Environnement, Terre, Eau
Spéciality : BIDAP – Biologie, Interactions, Diversité Adaptative des Plantes
Long-range K+ transport and adaptation to salt stress in rice: molecular and physiological analyses of the involvement of K+ channels
Manuel NIEVES-CORDONES, Chercheur, CEBAS-CSIC Murcia, Espagne – Rapporteur
Rob ROELFSEMA, Chercheur, Univ. Würzburg, Allemagne – Rapporteur
Pascal GANTET, Professeur, Univ. Montpellier, France – Examinateur
Tomoaki HORIE, Professeur, Univ. Shinshu, Japon – Examinateur
Yi WANG, Professeur, China Agricultural Univ., Chine – Examinateur
Mme Anne-Aliénor VERY, CR CNRS, Montpellier – Directrice de thèse
Rice high quality and yield requires the supply of K+, as that of other macronutrients. Efficient absorption of K+ by the roots from the soil solution and distribution of this cation within the plant, through long distance circulation via the xylem and phloem vasculature, the ascending flow being driven in part by the transpiration stream, is essential to support biomass and grain yield production, also in stressing environmental conditions such as soil salinity. The aim of my thesis was to study rice K+ transport systems involved in these key processes, for a better understanding of K+ transport mechanisms at the whole plant level, towards future development of more productive and salt stress adapted crops. In this study, a reverse genetics approach revealed that the outwardly-rectifying Shaker K+ channel OsK5.2 is a major determinant of plant growth upon saline conditions. Under salt treatment, qRT-PCR analysis showed that OsK5.2 expression was weakly affected in roots and rapidly upregulated in leaves. OsK5.2 mediated K+ efflux from guard cells limiting stomatal aperture was shown to minimize the Na+ flux arriving in shoots via the transpiration stream. OsK5.2 contribution to K+ loading into the xylem sap outperformed the negative effect of the decrease in xylem sap flow for shoot K+ feeding. OsK5.2 combined functions appeared, so, highly beneficial to the leaf K+ to Na+ homeostasis upon saline conditions and Na+ toxicity limitation. OsK5.2 was also revealed to be crucial for plant biomass production under limitation of the day light period, suggesting a role in phloem transport. OsK5.2 promoter GUS reporter fusions indicated localization of OsK5.2 expression in the phloem companion cells of root and shoot. By tracing K+ circulation in xylem and phloem saps, using Rb+, an important physiological contribution of OsK5.2 to K+ unloading from the phloem in roots was evidenced. In addition, analysis in rice and heterologously in Arabidopsis of another outward Shaker channel expressed in root vasculature, OsK5.1, suggested that this channel might play a role in xylem sap K+ loading, in addition to OsK5.2.