Plant Physiol, February 2002, Vol. 128, pp. 564-577

A Grapevine Gene Encoding a Guard Cell K⁺ Channel Displays Developmental Regulation in the Grapevine Berry

Biochimie et Physiologie Moléculaire des Plantes, Unité Mixte de Recherche 5004 Agro-M/Centre National de la Recherche Scientifique/Institut National de la Recherche Agronomique/Université Montpellier 2, 1 place Viala, F-34060 Montpellier cedex 1, France (R.P., B.L., F.G., J.-B.T., H.S.); Biologie du Développement des Plantes Pérennes Cultivées, Unité Mixte de Recherche 1098 Agro-M/Centre de Coopération Internationale en Recherche Agronomique pour le Développement/Institut National de la Recherche Agronomique/Institut de Recherche pour le Développement, 2 place Viala, F-34060 Montpellier cedex 1, France (L.T.); and Institut des Produits de la Vigne, Unité de Recherche de Biochimie Métabolique et Technologique, Agro-M/Institut National de la Recherche Agronomique, 2 place Viala, F-34060 Montpellier cedex 1, France (C.R.)

SIRK is a K⁺ channel identified in grapevine (Vitis vinifera), belonging to the so-called Shaker family. The highest sequence similarities it shares with the members of this family are found with channels of the KAT type, although SIRK displays a small ankyrin domain. This atypical feature provides a key to understand the evolution of the plant Shaker family. Expression in Xenopus laevis oocytes indicated that SIRK is an inwardly rectifying channel displaying functional properties very similar to those of KAT2. The activity of SIRK promoter region fused to the GUS reporter gene was analyzed in both grapevine and Arabidopsis. Like other KAT-like channels, SIRK is expressed in guard cells. In Arabidopsis, the construct is also expressed in xylem parenchyma. Semiquantitative reverse transcriptase-polymerase chain reaction experiments indicated that SIRK transcript was present at low levels in the berry, during the first stages of berry growth. After veraison, the period of berry development that corresponds to the inception of ripening and that is associated with large biochemical and structural modifications, such as evolution of stomata in nonfunctional lenticels and degeneration of xylem vasculature, the transcript was no longer detected. The whole set of data suggests that in the berries SIRK is expressed in guard cells and, possibly, in xylem tissues. The encoded channel polypeptide could therefore play a role in the regulation of transpiration and water fluxes in grapevine fruits.