Abstract
The grapevine (Vitis vinifera L.) is a fruit species with a major economic impact, widely cultivated for the production of wine grapes and therefore wine. This species is also considered a model plant for studying the physiology of plants with acid fruits. In grapevines, as in all plants, K+ plays a crucial role in numerous physiological mechanisms. During grape ripening, which is initiated by a key stage called veraison, K+ is accumulated in the berry. During ripening, this ion initiates and controls the massive flows of sugar and nutrients needed to load the berry. On the other hand, excessive accumulation of K+ in the grape berry leads to a reduction in must acidity, resulting in wines of poor organoleptic quality and impaired ageing potential. In this context, it seems crucial to understand the K+ flows involved in grape berry ripening. My work focused on characterising potassium channels belonging to the Shaker family. The various members of this family are known to dominate potassium conductance at the plasma membrane of plant cells. This 9-member family, divided into 5 subfamilies, has been extensively studied in the model plant A. thaliana. In grapevines, 9 members have also been identified. Surprisingly, however, we do not find the same distribution of subunits in the different subfamilies. For example, the outgoing subunit subfamily has 2 members in A. thaliana, whereas 4 members have been identified in grapevine. During my thesis, I studied these 4 subunits to understand their involvement in K+ transport in grapevine and berry loading during ripening. My thesis is divided into 3 parts. The first line of research involves the characterisation of VvK5.1, a typical outward Shaker subunit but with an extended expression territory, strongly suggesting the functional involvement of outward Shaker channels in new functions. The second axis presents the characterisation of VvK5.2. This sub-unit has a particular structural feature and appears to be fully adapted to the physiological needs of the grape berry during ripening. Finally, the two sub-units known as VvK5.3 and VvK5.4, which share 95% identity at peptide level but curiously differ in the presence of a mutation in the K+ selectivity motif, are grouped together in the last research area.