Isolation and characterization of MbWRKY1, a WRKY transcription factor gene from Malus baccata (L.) Borkh involved in drought tolerance

WRKY transcription factors are involved in stress responses in plants; however, their roles in abiotic stresses are still not well known in Malus plants. In the present study, a WRKY gene was isolated from Malus baccata (L.) Borkh and designated as MbWRKY1. Subcellular localization revealed that MbWRKY1 was localized in the nucleus. The expression levels of MbWRKY1 were up-regulated by dehydration, salinity, and ABA treatments in M. baccata seedlings. When MbWRKY1 was introduced into tobacco, it improved drought stress tolerance in transgenic plants. Under the drought treatment, transgenic plants had higher contents of chlorophyll, proline, relative water, AsA, and GSH than wild-type (WT) plants. Compared with WT plants, the overexpression of MbWRKY1 in transgenic tobacco also led to decreased levels of H2O2, MDA, and elecrolyte leakage when dealing with drought stress. There were increased activities of POD, CAT, SOD, and APX in transgenic tobaccos, especially when dealing with drought treatment. Moreover, the MbWRKY1 transgenic plants enhanced the expressions of oxidative stress response (NtPOD, NtCAT, NtSOD, and NtAPX) and stress-related genes (NtP5CS and NtLEA5) when dealing with drought stress. These results suggest that the MbWRKY1 gene plays a positive regulatory role in drought stress response.