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The WRKY-type transcription factors are involved in plant development and stress responses, but how the regulation of stress tolerance is related to plant development is largely unknown. GsWRKY20 was initially identified as a stress response gene using large-scale Glycine soja microarrays. Quantitative reverse transcription-PCR (qRT-PCR) showed that the expression of this gene was induced by abscisic acid (ABA), salt, cold, and drought. Overexpression of GsWRKY20 in Arabidopsis resulted in a decreased sensitivity to ABA during seed germination and early seedling growth. However, compared with the wild type, GsWRKY20 overexpression lines were more sensitive to ABA in stomatal closure, and exhibited a greater tolerance to drought stress, a decreased water loss rate, and a decreased stomatal density. Moreover, microarray and qRT-PCR assays showed that GsWRKY20 mediated ABA signalling by promoting the expression of negative regulators of ABA signalling, such as AtWRKY40, ABI1, and ABI2, while repressing the expression of the positive regulators of ABA, for example ABI5, ABI4, and ABF4. Interestingly, GsWRKY20 also positively regulates the expression of a group of wax biosynthetic genes. Further, evidence is provided to support that GsWRKY20 overexpression lines have more epicuticular wax crystals and a much thicker cuticle, which contribute to less chlorophyll leaching compared with the wild type. Taken together, the findings reveal an important role for GsWRKY20 in enhancing drought tolerance and regulating ABA signalling.

Salinity and alkalinity are the two main environmental factors that limit rice production. Better understanding of the mechanisms responsible for salinity and alkaline stress tolerance would allow researchers to modify rice to increase its resistance to salinity and alkaline stress. MicroRNAs (miRNAs) are ~21-nucleotide RNAs that are ubiquitous regulators of gene expression in eukaryotic organisms. Some miRNAs acts as an important endogenous regulator in plant responses to abiotic stressors. miR393 is a conservative miRNA family that occurs in a variety of different plants. The two members of the miR393 family found in rice are named osa-MIR393 and osa-MIR393b. We found that the osa-MIR393 expression level changed under salinity and alkaline stress, whereas that of osa-MIR393b did not. Target genes of osa-MIR393 were predicted, and some of these putative targets are abiotic related genes. Furthermore, we generated transgenic rice and Arabidopsis thaliana that over-expressed osa-MIR393, and the phenotype analysis showed that these transgenic plants were more sensitive to salt and alkali treatment compared to wild-type plants. These results illustrate that over-expression of osa-MIR393 can negatively regulate rice salt-alkali stress tolerance.

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