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

摘要

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 ofripening and that is associated with large biochemical and structuralmodifications, such as evolution of stomata in nonfunctional lenticelsand degeneration of xylem vasculature, the transcript was no longerdetected. The whole set of data suggests that in the berriesSIRK is expressed in guard cells and, possibly, in xylemtissues. The encoded channel polypeptide could therefore play a role inthe regulation of transpiration and water fluxes in grapevinefruits.