Grapevine Aquaporins: Gating of a Tonoplast Intrinsic Protein (TIP2;1) by Cytosolic pH LeitãoLuís PristaCatarina F. MouraTeresa C. Loureiro-DiasMaria SoveralGraça 2012 <div><p>Grapevine (<em>Vitis vinifera</em> L.) is one of the oldest and most important perennial crops being considered as a fruit ligneous tree model system in which the water status appears crucial for high fruit and wine quality, controlling productivity and alcohol level. <em>V. vinifera</em> genome contains 28 genes coding for aquaporins, which acting in a concerted and regulated manner appear relevant for plant withstanding extremely unfavorable drought conditions essential for the quality of berries and wine. Several <em>Vv</em> aquaporins have been reported to be expressed in roots, shoots, berries and leaves with clear cultivar differences in their expression level, making their <em>in vivo</em> biochemical characterization a difficult task. In this work <em>V. vinifera cv.</em> Touriga nacional <em>Vv</em>Tn<em>PIP1;1</em>, <em>Vv</em>Tn<em>PIP2;2</em> and <em>Vv</em>Tn<em>TIP2;1</em> were expressed in yeast and water transport activity was characterized in intact cells of the transformants. The three aquaporins were localized in the yeast plasma membrane but only <em>Vv</em>TnTIP2;1 expression enhanced the water permeability with a concomitant decrease of the activation energy of water transport. Acidification of yeast cytosol resulted in loss of <em>Vv</em>TnTIP2;1 activity. Sequence analysis revealed the presence of a His<sup>131</sup> residue, unusual in TIPs. By site directed mutagenesis, replacement of this residue by aspartic acid or alanine resulted in loss of pH<sub>in</sub> dependence while replacement by lysine resulted in total loss of activity. In addition to characterization of <em>Vv</em>Tn aquaporins, these results shed light on the gating of a specific tonoplast aquaporin by cytosolic pH.</p> </div>