Salicylic acid reduces MdPUB24-mediated ubiquitination of MdWRKY40 to suppress ethylene biosynthesis in apple fruit

The plant hormone salicylic acid (SA) effectively suppresses ethylene biosynthesis in apple (<i>Malus domestica</i>) fruit. However, the underlying molecular mechanism remains unclear. Here, we identified a WRKY transcription factor, <i>MdWRKY40</i>, which was upregulated in response to SA treatment. MdWRKY40 functioned as a transcriptional repressor of the ethylene biosynthesis gene <i>MdACS1</i> (1<i>-aminocyclopropane-1-carboxylic acid synthase 1</i>). In addition, we found that the expression of U-box-type E3 ubiquitin ligase <i>MdPUB24</i> was downregulated following SA treatment. MdPUB24 interacted with MdWRKY40 and mediated its ubiquitination, leading to the degradation of MdWRKY40 via the 26S proteasome pathway, which was suppressed by SA. Together, these results suggest that the MdPUB24<i>-</i>MdWRKY40<i>-MdACS1</i> regulatory module mediates SA-induced suppression of ethylene biosynthesis by post-translational modification during apple fruit ripening. These findings offer new insights into the molecular basis of fruit ripening inhibition and shelf-life extension.