OsWRKY28 positively regulates salinity tolerance by directly activating OsDREB1B expression in rice

OsWRKY28 confers salinity tolerance by directly binding to OsDREB1B promoter and increasing its transcriptional activity, and negatively regulates abscisic acid mediated seedling establishment in rice. WRKY transcription factors have been reported to play a vital role in plants growth, development, abiotic and biotic stress responses. In this study, we explored the functions of a transcription factor OsWRKY28 in rice. The transcript level of OsWRKY28 was strikingly increased under drought, chilling, salt and abscisic acid treatments. The OsWRKY28 overexpression lines showed enhanced salinity stress tolerance, whereas the oswrky28 mutants displayed salt sensitivity compared to wild-type plants. Under salt stress treatment, the expression levels of OsbZIP05, OsHKT1;1 and OsDREB1B were significantly lower yet the level of OsHKT2;1 was significantly higher in oswrky28 mutants than those in wide type plants. Our data of yeast one-hybrid assay and dual-luciferase assay supported that OsWRKY28 could directly bind to the promoter of OsDREB1B to enhance salinity tolerance in rice. In addition, OsWRKY28 overexpression lines displayed hyposensitivity and the oswrky28 mutants showed hypersensitivity compared to wild-type plants under exogenous abscisic acid treatment. Based on the results of yeast two-hybrid assay and GAL4-dependent chimeric transactivation assay, OsWRKY28 physically interacts with OsMPK11 and its transcriptional activity could be regulated by OsMPK11. Together, OsWRKY28 confers salinity tolerance through directly targeting OsDREB1B promoter and further activating its transcription in rice.