Doctorate thesis

Monday, December 16, 2013


Molecular identification, functional characterization and transcriptional regulation analysis of the Shaker potassium channel in Vitis vinifera and Arabidopsis thaliana

Mamy Adrianteranagna
BPMP, “Ion Channels” team


Jury :
Christian MAZARS, DR-CNRS, Rapporteur
Nathalie LEONHARDT, CR-CEA, Rapporteur
Alain VAVASSEUR, DR-CEA, Examinateur
Thierry SIMONNEAU, DR-INRA, Examinateur
Isabelle GAILLARD, CR-INRA, Directeur de thèse
Hervé SENTENAC, DR-INRA, Directeur de thèse


Abstract :
The Shaker family (nine members in grapevine (Vitis Vinifera) and in Arabidopsis thaliana) encodes voltage-gated K+ channels that dominate the membrane K+ conductance and provide major pathways for wholesale K+ uptake or secretion in most tissues and cell types. In Arabidopsis thaliana, a significant amount of information has been obtained for Shaker channel functional properties, post-translational regulations and roles in planta since the identification of the first K+ Shaker channel in 1992. In contrast, no significant attempt was made to unravel the molecular mechanism involved their regulation at the transcriptional level. In the first part of this manuscript, an analysis of the regulation of the Arabidopsis SKOR (Stelar K+ outward rectifier) Shaker gene at the transcriptional level is reported. Real time RT-qPCR analysis reveals that SKOR, which is expressed in the root pericycle and involved in the K+ release into the xylem sap, is drastically down regulated upon water stress and ABA exposure. SKOR promoter deletion study was performed and a zone of 236 bp involved in this regulation was identified. ABRE and DRE/CRT cis specific elements involved in the ABA response are present in this zone. The second part of this thesis is aimed at valorizing information gained from the model plant Arabidopsis thaliana by transfer towards an economically important plant namely grapevine. In grapevine, K+ accumulation in grape berries results in decreased must acidity, leading to wines with low organoleptic properties. In order to identify how K+ is taken up and accumulated during berry development and upon abiotic (drought and heat) stress, molecular determinants of K+ transport in grapevine are looked for. Here two K+ Shaker subunits have been cloned and characterized at the functional level. VvK1.2 is specifically expressed in the berry, where it displays a very strong induction at veraison (the inception of ripening) in flesh cells. Its expression in thesecells is further strongly increased upon mild drought stress. VvK1.2 acts as a voltage gated inwardly rectifying K+ channel when co-expressed with its specific CBL-interacting protein kinase (CIPK)/calcineurinB-like calcium sensor (CBL) pairs. This channel is likely to play a major role in K+ transport in flesh cells of the developing berry in relation with grape acidity. The second channel, named VvK3.1 is mainly expressed in the phloem tissues throughout the plant in both source and sink organs. VvK3.1 is a weakly inwardly rectifying K+ channel, involved in long distance K+ transport via the phloem sap and in K+ loading of the berry after véraison. Moreover, high amounts of VvK3.1 transcripts have been detected in the grapevine pulvinus, a structure not already described in this species. Indeed, VvK3.1 may thus be involved in leaf movements in grapevine.