Grapevine Aquaporins: Gating of a Tonoplast Intrinsic Protein (TIP2;1) by Cytosolic pH

Abstract

Grapevine (Vitis vinifera 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. V. vinifera 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 Vv aquaporins have been reported to be expressed in roots, shoots, berries and leaves with clear cultivar differences in their expression level, making their in vivo biochemical characterization a difficult task. In this work V. vinifera cv. Touriga nacional VvTnPIP1;1, VvTnPIP2;2 and VvTnTIP2;1 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 VvTnTIP2;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 VvTnTIP2;1 activity. Sequence analysis revealed the presence of a His131 residue, unusual in TIPs. By site directed mutagenesis, replacement of this residue by aspartic acid or alanine resulted in loss of pHin dependence while replacement by lysine resulted in total loss of activity. In addition to characterization of VvTn aquaporins, these results shed light on the gating of a specific tonoplast aquaporin by cytosolic pH.

Roles of Aquaporins in Setaria viridis Stem Development and Sugar Storage

“…Gating of water channel activity has been reported for PIPs, including SvPIP2;1 ( Figure 5B ), and for the TIP2;1 isoform found in grapevine (Törnroth-Horsefield et al, 2006; Leitao et al, 2012; Frick et al, 2013). The mechanism of pH gating for these AQPs is the protonation of a Histidine residue located on the cytoplasmic Loop D where site-directed mutagenesis studies of the Loop D His residue results in a loss of pH dependent water permeability (Tournaire-Roux et al, 2002; Leitao et al, 2012; Frick et al, 2013). However, although SvNIP2;2 water permeability was pH dependent the predicted Loop D structure does not contain a His residue (Supplementary Figure S5), hence for SvNIP2;2 the mechanism for pH gating is not clear.…”

Rat Aquaporin-5 Is pH-Gated Induced by Phosphorylation and Is Implicated in Oxidative Stress

“…AQPs can be subjected to regulation via different mechanisms, among which pH regulation has been disclosed for plant [28] and for a few mammalian AQPs, such as AQP0, AQP3, and AQP6 [30,31,32]. It is also known that eukaryotic AQPs can be gated by phosphorylation [24].…”

“…Yeast cells lacking endogenous AQPs have been used to detect water transport capacity of mammalian [26,27] and plant [28,29] aquaporins and recently we used this system to characterize the pH gating of AQP3 [27]. …”

Functional characterization of FaNIP1;1 gene, a ripening-related and receptacle-specific aquaporin in strawberry fruit

“…Functional studies of FaNIP1;1 protein using yeast as a heterologous experimental system Previous reports showed that the expression of a TIP2;1 aquaporin from grape (VvTIP2;1) in S. cerevisiae decreased resistance to osmotic stress [66]. This prompted us to analyze the effect of the FaNIP1;1 protein expression in yeast under similar physiological conditions.…”