Eggplant WRKY26 functions as a positive regulator of cold tolerance by inducing autophagy

Eggplant (Solanum melongena L.), a thermophilic plant, is highly susceptible to cold stress, which significantly impacts its growth and productivity. While WRKY transcription factors are known to play key roles in plant responses to environmental stresses, their involvement in cold stress tolerance in eggplant remains largely unexplored. Here, we identified and characterized SmWRKY26, a group I WRKY transcription factor closely related to SlWRKY33 and AtWRKY26. Subcellular localization and transcriptional activating activity assays confirmed that SmWRKY26 was a nuclear-localized transcriptional activator. Expression analysis revealed that SmWKRY26 was induced by exogenous hormones and cold stress. Overexpression of SmWRKY26 in eggplant enhanced cold tolerance by promoting the stability of plasma membrane, maintaining photosynthetic efficiency, enhancing the capability of antioxidants, and accelerating the degradation of insoluble protein. In contrast, SmWRKY26 gene knockout mutants showed the opposite trend. RNA-seq results revealed that SmWRKY26 mainly regulated genes in the mRNA surveillance pathway, protein processing in the endoplasmic reticulum and autophagy. Further experiment verified that SmWRKY26 positively regulated the expression of autophagy-related genes and facilitated the formation of autophagosomes under cold stress. These findings highlight a novel regulatory mechanism for cold stress tolerance mediated by SmWRKY26 in eggplant, offering a valuable genetic resource for developing cold-tolerant cultivars.