Transcriptomic and metabolic analyses provide new insights into chilling injury in peach fruit

Low temperature conditioning (LTC) alleviates peach fruit chilling injury but the underlying molecular basis is poorly understood. Here, changes in transcriptome, ethylene production, flesh softening, internal browning and membrane lipids were compared in fruit maintained in constant 0 degrees C and LTC (pre-storage at 8 degrees C for 5 d before storage at 0 degrees C). Low temperature conditioning resulted in a higher rate of ethylene production and a more rapid flesh softening as a result of higher expression of ethylene biosynthetic genes and a series of cell wall hydrolases. Reduced internal browning of fruit was observed in LTC, with lower transcript levels of polyphenol oxidase and peroxidase, but higher lipoxygenase. Low temperature conditioning fruit also showed enhanced fatty acid content, increased desaturation, higher levels of phospholipids and a preferential biosynthesis of glucosylceramide. Genes encoding cell wall hydrolases and lipid metabolism enzymes were coexpressed with differentially expressed ethylene response factors (ERFs) and contained ERF binding elements in their promoters. In conclusion, LTC is a special case of cold acclimation which increases ethylene production and, operating through ERFs, promotes both softening and changes in lipid composition and desaturation, which may modulate membrane stability, reducing browning and contributing to alleviation of peach fruit chilling injury.