Isolation and preliminary functional characterization of MxWRKY64 , a new WRKY transcription factor gene from Malus xiaojinensis Cheng et Jiang

Malus xiaojinensis Cheng et Jiang is a special and significant germplasm resource of semi-dwarf apple in China. Abiotic stresses, such as Fe and high salinity, affect Malus xiaojinensis growth and development. WRKY transcription factors (TFs) are widely involved in the responses of plants to different stresses. In the present study, a new WRKY gene was isolated from Malus xiaojinensis and designated as MxWRKY64. Subcellular localization showed that MxWRKY64 was a nucleus localized protein. The expression level of MxWRKY64 was highly affected by Fe and salt stress in M. xiaojinensis seedlings. When MxWRKY64 was introduced into Arabidopsis thaliana, it greatly increased the Fe and salt tolerance in transgenic plant. When dealt with Fe stress, overexpression of MxWRKY64 in transgenic A. thaliana contributed to higher levels of fresh weight, root length, and contents of chlorophyll and Fe than wild type (WT). Increased expression of MxWRKY64 in transgenic A. thaliana also resulted in higher activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), higher contents of proline and chlorophyll, while malondialdehyde (MDA) content was lower, especially in response to salt stress. Therefore, these results suggest that MxWRKY64 probably plays an important role in response to Fe and salt stress in Arabidopsis.