Characterization of grapevine K+ channels and their implication in berry development and quality

SIRK and SOR are two Shaker-like K+ channels identified in Vitis vinifera. They are both expressed in the aerial parts of the plant, including the berry. By a reporter gene approach, SIRK expression pattern was shown to be restricted to the stomata guard cells. Quantitative RNA-PCR experiments indicated that SIRK transcript is present in the berry during the first stages of berry growth. After veraison, the transcript is no longer detected, suggesting that SIRK could be expressed in berry guard cells too. Expression in Xenopus oocytes indicated that SIRK is an inwardly-rectifying channel. The present data and the high level of similarity between SIRK and Arabidopsis KAT2 channel suggest that SIRK is involved in stomata aperture and could therefore play a role in the regulation of transpiration and water fluxes in grapevine. SOR transcript accumulation in the berry was shown to decrease slightly but regularly after veraison. Electrophysiological analyses indicated that SOR is endowed with outwardly-rectifying properties. A dominant negative mutant form of the channel was expressed in transgenic grapevines. The resulting plantlets exhibited impaired growth and increased needs in K+. The phenotype of older, greenhouse-grown plants is still under investigation.