UDP-glycosyltransferase PpUGT74F2 is involved in fruit immunity via modulating salicylic acid metabolism

Flesh fruits are essential for human health, but pathogen infection poses a threat to fruit production and postharvest storage. The hormone salicylic acid (SA) and its metabolites, such as sugar conjugates and methyl salicylate (MeSA), play a crucial role in regulating plant immune responses. However, the UDP-glycosyltransferases (UGTs) responsible for modulating SA metabolism in fruit have yet to be identified, and further investigation is needed to elucidate its involvement in fruit immune response. Here, we identified PpUGT74F2 as an enzyme with the highest transcription level in peach fruit, responsible for catalyzing the biosynthesis of SA glucoside (SAG), but not for MeSAG formation in fruit. Furthermore, infection of peach fruit with Monilinia fructicola, which causes brown rot disease, led to reduced expression of PpUGT74F2, resulting in a significant decrease in SAG content and an increase in MeSA levels. Transgenic tomatoes expressing heterologous PpUGT74F2 increased susceptibility to gray mold. Interestingly, overexpressing PpUGT74F2 did not affect SA levels but dramatically reduced MeSA levels in response to pathogen infection, accompanied by significantly reduced expression of pathogen-related (PR) genes in transgenic tomatoes. This study highlights that PpUGT74F2 acts as a negative regulatory factor for fruit immunity through a distinct mechanism not previously reported in plants.