Overexpressing VvWRKY18 from grapevine reduces the drought tolerance in Arabidopsis by increasing leaf stomatal density

The growth of grapevine [Vitis vinifera L.] is commonly limited by drought stress. The mechanisms by which grapevine copes with drought stress have not yet been extensively clarified. In this study, the drought and abscisic acid (ABA)-induced gene VvWRKY18 was demonstrated to decreased drought tolerance of Arabidopsis thaliana overexpression (VvWRKY18-OE) lines. Compared to wild-type plants, VvWRKY18-OE lines showed increased levels of malonaldehyde (MDA) and the reactive oxygen species (ROS) H2O2 and O2− decreased levels of proline, weakened activity of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), and decreased sensitivity to ABA with respect to stomatal closure.VvWRKY18-OE lines also showed an increase in stomatal density and a higher water loss rate. Negative regulators of stomatal development including SDD1, YDA, TMM, and MPK6, were downregulated in VvWRKY18-OE lines. Transcript levels of the stress-related genes DREB1A and CBF2 were significantly reduced in VvWRKY18-OE lines under drought stress. Taken together, these findings demonstrate that VvWRKY18 reduced drought tolerance in Arabidopsis. Our results contribute to understanding of the roles that WRKY genes play in drought stress and stomatal development.