The miR156/SPL module regulates apple salt stress tolerance by activating MdWRKY100 expression

Salt stress dramatically impedes plant growth and development as well as crop yield. The apple production regions are reduced every year, because of the secondary salt damage by improper fertilization and irrigation. To expand the cultivation area of apple (Malus domestica) and select salt-resistant varieties, the mechanism of salt tolerance in apple is necessary to be clarified. The miR156/SPL regulatory module plays key roles in embryogenesis, morphogenesis, life cycle stage transformation, flower formation and other processes. However, its roles in the mechanisms of salt tolerance are unknown. In order to elucidate the mechanism of 156/SPL regulating salt stress in apple, we performed RLM-5' RACE and stable genetic transformation technology to verify that both mdm-MIR156aandMdSPL13responded to salt stress in apple and that the latter was the target of the former.MIR156aoverexpression weakened salt resistance in apple whereasMdSPL13overexpression strengthened it. A total of 6094 differentially expressed genes relative to nontransgenic apple plants were found by RNA-Seq analysis of MdSPL13OE. Further verification indicated that MdSPL13 targeted theMdWRKY100gene promoter. Moreover,MdWRKY100overexpression enhanced salt tolerance in apple. Our results revealed that the miR156/SPL module regulates salt tolerance by up-regulatingMdWRKY100in apple. This study is the first to elucidate the mechanism underlying the miRNA network response to salt stress in apple and provides theoretical and empirical bases and genetic resources for the molecular breeding of salt tolerance in apple.