Abstract
WRKY transcription factors (TFs) 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 TFs, WRKY70 and WRKY54, to osmotic stress tolerance. These TFs 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 TFs 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 WRKY70 and WRKY54 co-operate as negative regulators of stomatal closure and, consequently, osmotic stress tolerance in Arabidopsis, suggesting that they have an important role, not only in plant defense, but also in abiotic stress signaling.
Highlights
In their natural environment, plants are confronted with a series of biotic and abiotic stresses that detrimentally affect their growth and development
To explore the possible involvement of WRKY54 and WRKY70 in abiotic stress responses, we first characterized the expression of the corresponding genes in wild-type Arabidopsis exposed to osmotic stress (15% PEG6000)
As genes responsive to osmotic stress and osmoprotectants were not implicated in osmotic stress tolerance of the wrky54wrky70 mutants, we explored the involvement of water balance regulation to explain the observed tolerance phenotype
Summary
Plants are confronted with a series of biotic and abiotic stresses that detrimentally affect their growth and development. Osmotic stress, which results in cellular water deficit, is one of the most limiting factors of plant growth, distribution and crop productivity, and poses a serious threat to the agricultural industry worldwide (Rabbani et al, 2003). The disruption of plant water status and low water potential can be caused by a number of factors, such as decreased water availability in the soil during drought, reduced water uptake as a result of high salinity or freeze-induced cellular dehydration (Verslues et al, 2006). To respond to osmotic stress, plants have evolved complex adaptive strategies that help to avoid or tolerate cellular dehydration, allowing plants to grow and complete their life cycles. Tolerance to osmotic stress includes enhanced expression of stressresponsive genes and metabolic adjustments, resulting in the accumulation of osmolytes, protective solutes and proteins (Xiong et al, 1999; Verslues et al, 2006; Shinozaki & YamaguchiShinozaki, 2007)
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