The grapevine tonoplast aquaporin TIP2;1 is a pressure gated water channel

In plants, the vacuole is a multifunctional organelle with an important role in the maintenance of the intracellular space. Tonoplast membranes are highly permeable to water due to their content in aquaporins TIPs (Tonoplast Intrinsic Proteins) that allow the rapid water influx creating an internal turgor pressure responsible for cell expansion, elongation and shape. The aim of the present study was to evaluate if the grapevine Vitis vinifera TIP2;1 would operate as a possible volume regulator gated by membrane surface tension. For that, the wild type VvTIP2;1 and a non-functional mutated form were heterologous expressed in yeast. Using an experimental strategy in which cells are incubated in external media that induce an increase in internal hydrostatic pressure and consequently membrane surface tension, we were able to compare the osmotic permeability (Pf) and the activation energy for water transport (Ea) of yeast strains expressing the functional and a non-functional TIP2;1. We found Pf and Ea dependence on internal turgor pressure only for the strain harboring the functional aquaporin indicating that TIP2;1 activity is regulated by membrane tension changing from an open to a closed state in an internal pressure dependent manner. This turgor dependent gating of TIP2;1 might be a mechanism to regulate vacuolar size and shape in plants withstanding hostile drought conditions such as grapevine.