Regulation of ethyl ester synthesis in two apple (Malus domestica) cultivars: Insights from integrated metabolomic and transcriptomic analyses.

Although ethyl esters are known to accumulate under hypoxic conditions, their biosynthetic regulation during senescence under aerobic conditions remains unclear. We hypothesized that ethylene could play a pivotal role in the ethyl ester synthesis under aerobic conditions. We conducted an integrated analysis of metabolite and transcript profiles over time using 'Orin' and 'Shinano Gold' apples, both with and without 1-MCP treatment. Comparative analysis of the ethanol pathway and ethyl ester-related genes revealed that two PDC genes, MdPDC2 and MD04G1159900, are rate-limiting for ethyl ester synthesis in 'Orin', in proportion to ethylene production. In contrast, ethanol and ethyl ester concentrations in 'Shinano Gold' were lower than expected based on ethylene production, suggesting that PDC and/or ADH function in the ethanol synthesis may be impaired. These regulatory mechanisms governing ethyl ester synthesis during aerobic ripening provide valuable insights for optimizing storage strategies and for breeding cultivars with enhanced aroma profiles.