The transcription factor MdWRKY9 is involved in jasmonic acid-mediated salt stress tolerance in apple

Salt stress is an important abiotic stress affecting the growth and fruit quality of apple fruits. Although jasmonic acid (JA) hormones and WRKY transcription factors (TFs) have both been reported to be involved in plant salt stress responses, the molecular mechanisms by which JA-mediated WRKY TFs regulate salt stress in apples remain unclear. Here, we report the identification of a WRKY family TF from apple, MdWRKY9, and its involvement in apple salt tolerance by regulating the expression of Na⁺/H⁺ antiporters, MdNHX1, and MdSOS2. Furthermore, we show that the protein repressors MdJAZ5 and MdJAZ10 in the JA signaling pathway can both interact with MdWRKY9 to form a complex and inhibit its DNA-binding and transcriptional activation activity. The JA signal triggers the degradation of MdJAZ5 and MdJAZ10 proteins by the 26S proteasome, disrupting the JAZ-WRKY protein complex and thereby releasing MdWRKY9 to activate downstream gene expression, promoting salt tolerance in apples. These findings provide important insights into the molecular mechanism of the WRKY TFs in JA-mediated salt tolerance in plants.