Summary WRKY transcription factors ( TF s) have been mainly associated with plant defense, but recent studies have suggested additional roles in the regulation of other physiological processes. Here, we explored the possible contribution of two related group III WRKY TF s, WRKY 70 and WRKY 54, to osmotic stress tolerance. These TF s are positive regulators of plant defense, and co‐operate as negative regulators of salicylic acid ( SA ) biosynthesis and senescence. We employed single and double mutants of wrky54 and wrky70 , as well as a WRKY70 overexpressor line, to explore the role of these TF s in osmotic stress (polyethylene glycol) responses. Their effect on gene expression was characterized by microarrays and verified by quantitative PCR . Stomatal phenotypes were assessed by water retention and stomatal conductance measurements. The wrky54wrky70 double mutants exhibited clearly enhanced tolerance to osmotic stress. However, gene expression analysis showed reduced induction of osmotic stress‐responsive genes in addition to reduced accumulation of the osmoprotectant proline. By contrast, the enhanced tolerance was correlated with improved water retention and enhanced stomatal closure. These findings demonstrate that WRKY 70 and WRKY 54 co‐operate as negative regulators of stomatal closure and, consequently, osmotic stress tolerance in A rabidopsis , suggesting that they have an important role, not only in plant defense, but also in abiotic stress signaling.

Defense‐related transcription factors <scp>WRKY</scp>70 and <scp>WRKY</scp>54 modulate osmotic stress tolerance by regulating stomatal aperture in <i><scp>A</scp>rabidopsis</i>

Defense‐related transcription factors WRKY70 and WRKY54 modulate osmotic stress tolerance by regulating stomatal aperture in Arabidopsis