A WRKY Transcription Factor PmWRKY57 from Prunus mume Improves Cold Tolerance in Arabidopsis thaliana

Prunus mume, a woody perennial tree, is valued for its ornamental traits and has been cultivated for a long history. Low temperature is the main environmental factor restricting the distribution and affecting the growth of P. mume. In plants, some WRKY transcription factors have been reported to participate in regulating cold tolerance. However, there were few researches about functional characterization of WRKYs involving in P. mume cold response. Here, a cold-induced WRKY gene named as PmWRKY57 was cloned from a P. mume cultivar 'Guhong Zhusha.' PmWRKY57 protein harboring a WRKY domain and a C2H2 zinc finger motif belongs to Group IIc of WRKY family. The PmWRKY57 protein was located to the nucleus and has transcriptional activation activity. PmWRKY57-overexpresing Arabidopsis thaliana lines showed improved cold tolerance, compared to wild-type plants. Under cold treatment, the leaves of transgenic lines contained significantly lower malondialdehyde content, and higher levels of superoxide dismutase activity, peroxidase activity, and proline content than wild-type plants. Furthermore, the expression levels of cold-response genes such as AtCOR6.6, AtCOR47, AtKIN1, and AtRCI2A were up-regulated in leaves of transgenic A. thaliana compared to those in wild-type plants. This study characterized the function of PmWRKY57 in improving cold tolerance of plants.