MdWRKY61 enhances apple resistance to Colletotrichum fructicola through jasmonic acid signaling pathway

MdWRKY61 enhances jasmonic acid signal transduction by inhibiting the expression of MdJAZ1, a negative regulator in the jasmonic acid signaling pathway, thereby increasing apple resistance to Colletotrichum fructicola. Glomerella leaf spot (GLS), a fungal disease caused by Colletotrichum species, poses a significant threat to the global apple industry. The WRKY transcription factor family plays a crucial role in plant defense responses; however, their specific functions and the mechanisms underlying resistance to GLS remain poorly understood. In this study, MdWRKY61 overexpression lines and wild-type (WT) plants were inoculated with Colletotrichum fructicola to assess GLS resistance. At 4 days post-inoculation, overexpression lines exhibited a 45.4% ~ 50.0% lower disease incidence and a 22.0 ~ 29.3 reduction in disease index compared to WT. Physiological assays showed decreased hydrogen peroxide and superoxide anion levels, alongside elevated superoxide dismutase and peroxidase activities in overexpression lines. These findings indicate that overexpression of MdWRKY61 enhances resistance to C. fructicola in apple and alleviates oxidative damage induced by pathogen infection. Hormone analyses revealed that the overexpression of MdWRKY61 enhanced the accumulation of jasmonic acid (JA), and in vitro tests confirmed that JA treatment significantly suppressed C. fructicola mycelial growth. Molecular biological experiments revealed that MdWRKY61 directly binds to the W-box element (TTGACT) in the promoter region of MdJAZ1, a negative regulator in the JA signaling pathway, thereby inhibiting its transcriptional expression. Collectively, these findings suggest that MdWRKY61 enhances JA signal transduction by downregulating MdJAZ1, thereby increasing apple resistance to GLS. These results highlight MdWRKY61 as a promising candidate for genetic engineering to develop novel disease-resistant apple cultivars.