Objective To explore the role of MfWRKY22 transcription factor in response to salt, drought and low temperature stresses in Medicago falcata, and to provide a theoretical basis for further investigating the molecular mechanism of MfWRKY22 in M. falcata responding to the abiotic stresses. Method Based on the RNA-Seq data of M. falcata treated with salt and drought, MfWRKY22 gene and its promoter sequence were cloned respectively by RT-PCR and Genome Walker method, and the bioinformatics, gene expression, subcellular localization and transcriptional activation activity analysis were performed. Meanwhile, the OE-MfWRKY22 transgenic Arabidopsis lines were constructed, and the fresh weight, root length and lateral root number of transgenic Arabidopsis seedlings were determined respectively at the day 10 of salt, drought and low temperature stresses treatments. Result The CDS of MfWRKY22 is 1 017 bp, encoding a protein with 338 amino acids, with predicted molecular mass of 37.05 kD and an isoelectric point of 5.65. MfWRKY22, localized in the nucleus and with transcriptional activation activity, is a Group Ⅱ member. A 1 888 bp sequence of MfWRKY22 promoter was obtained, and the cis-acting elements, such as salt stress induction, drought responsive, osmotic stress responsive, ethylene responsive and W-box, were identified. Meanwhile, it was found that the MfWRKY22 gene had the highest expression in the leaves of M. falcata, and the expressions of MfWRKY22 gene in the roots, stems and leaves were up-regulated after salt, drought and low temperature treatment. Under salt, drought and low temperature stresses, the fresh weight, root length and lateral root number of transgenic Arabidopsis seedlings were higher than that of wild seedlings. Conclusion MfWRKY22, whose expression is up-regulated by salt, drought and low temperature stresses,is a Group Ⅱ WRKY transcription factor member, and the overexpressing MfWRKY22 could improve the growth of transgenic plants under abiotic stresses.
