Transcriptional and post-transcriptional regulation by sugar of the grape monosaccharide transporter VvHT1

Abstract

Sugars are massively imported from leaves into grape berry flesh cells during maturation, involving both sucrose and monosaccharide transporters. Several VvHT (Vitis vinifera Hexose Transporter) genes have been cloned that display different patterns of expression during ripening. In V. vinifera heterotrophic suspension cultured cells we previously identified and characterized a H+-dependent glucose transport system and RNA gel blot analysis suggested that VvHT1 has a major contribution for the observed transport activity. In the present work, we report that VvHT1 expression and glucose transport are tightly regulated by glucose in grape suspension cells. RNA blot analysis demonstrated that VvHT1 transcription was strongly repressed by 150 mM glucose, and 2-deoxy-D-glucose, but neither by 3-O-methyl-D-glucose (3-O-MeG) nor by glucose plus mannoheptulose, indicating the involvement of a hexokinase mediated pathway. 3-O-MeG induced a decrease of transport activity caused by the reduction of VvHT1 protein in the plasma membrane, without affecting VvHT1 transcripts levels, demonstrating post-transcriptional regulation. Depending on the sugar status of the medium, glucose up- or down regulated VvHT1 transcripts and glucose uptake. The present data shows that plant sugar transporters can be regulated by its own substrate both at transcriptional and post-transcriptional levels.