Doctorate thesis of Montpellier SupAgro

Wednesday, December 11, 2019

at 2 pm – Campus de La Gaillarde – Amphi 208 (School Heart)

Identification and characterization of grapevine K+ Shaker channels involved in the control of berry acidity

BPMP, Kaliphruit team

Doctoral School: GAIA – Biodiversity, Agriculture, Food, Environment, Land, Water
Speciality : BIDAP – Biology, Interactions, Adaptive Plant Diversity
Institution : Montpellier SupAgro

Jury :
Mme Fatma OUAKED-LECOURIEUX, Chargée de recherche, CNRS Bordeaux – UMR EGFV Rapporteure
M. Sébastien THOMINE, Directeur de recherche, CNRS Paris – UMR I2BC Rapporteur
Mme Nathalie LEONHARDT, Chercheuse CEA, CEA Cadarache Examinatrice
M. Thierry SIMONNEAU, Directeur de recherche, INRA Montpellier – UMR LEPSE Examinateur
Mme Isabelle GAILLARD, Directrice de recherche, INRA Montpelllier – UMR BPMP Directrice de thèse
Mme Teresa CUELLAR-SANCHEZ, Chercheuse CIRAD, CIRAD Montpellier – UMR AGAP Co-directrice de thèse

Grapevine (Vitis vinifera L.) is a fruit species with high economic impact largely cultivated for wine production. This species is also considered as a model plant for studying the physiology of acidic fruit development. In grapevine, as for all plants, K + plays a crucial role in many physiological mechanisms. During berry ripening, which is initiated by a key step called veraison, the K + is strongly accumulated in berry cells. During this maturation phase, K + also initiates and controls the massive fluxes of sugar and nutrients loaded in berry. However, an excessive accumulation of K + in the fruit causes a decrease of acidity of the must resulting to the production of low quality wines with a poor potential of aging. In this context, understanding K + fluxes occurring during the maturation of berries is crucial. My work focused on the characterization of K + channels belonging to the Shaker family that is known to dominate the K + conductance in plant cell plasma membrane. This family with nine sub-units divided into five subfamilies has been largely studied in the A. thaliana model plant. Similarly, 9 shaker sub-units have also been identified in grapevine genome but, surprisingly, the numbers of members within each group are not strictly conserved between the two species. Indeed, the sub-family of outward sub-units contains 2 members in A. thaliana while 4 members have been identified in vine. During my thesis, I studied the 4 VvK5s outward subunits from grapevine to understand their involvement in the transport of K + during the ripening phase of the berry. In this context, my thesis is divided into 3 axes. The first axis is a characterization of VvK5.1, a typical outward rectifying K + Shaker channel with an extended territory of expression strongly suggesting his involvement in new functions for outward subunits. The second axis is the characterization of VvK5.2, a subunit with structural and functional features completely adapted to the specific physiological needs for a complete nutrient loading of grape berry. Finally, the last research axis focus on the two subunits VvK5.3 and VvK5.4 that share 95% of identity at the peptidic level but curiously differ by a mutation that changes one aminoacid in the K + selectivity motif.

Keywords : grapevine, potassium, K+ Shaker channels, berry acidity