Transcriptome and Metabolomic Analysis to Reveal the Browning Spot Formation of ‘Huangguan’ Pear

Background: Browning spot (BS) disorders seriously affect the appearance quality of ‘Huangguan’ pear and cause economic losses. Many studies on BS have mainly focused on physiological and biochemical aspects, and the molecular mechanism is unclear. Result: In the present study, the structural characteristics of ‘Huangguan’ pear with BS were observed with SEM, the water loss and brown spot were evaluated, and transcriptome and metabonomics analyses were conducted to reveal the molecular mechanism of ‘Huangguan’ pear skin browning disorder. The results showed that the occurrence of BS was accompanied by a decrease in the wax layer and an increase in lignified cells. It appears that genes related to wax biosynthesis were down-regulated in BS, resulting in the decrease of wax layer in BS. Genes related to lignin were up-regulated at transcriptional level, resulting in upregulation of metabolites related to phenylpropanoid biosynthesis. Expression of calcium-related genes were upregulated in BS. The cold-induced genes CS120, LTI65 and RCI2B may be the key genes that induce BS. In addition, the results demonstrated that exogenous NaH2PO4·2H2O and ABA treatment could inhibit the incidence of BS during harvest and storage time by increasing the expression of wax-related genes and calcium-related genes and increasing plant resistance, whereas GA3may accelerate the incidence and index of BS in transcriptomics. Conclusions: The results of this study would provide a basis for the molecular mechanism of BS formation and clarify the effects of different treatments on the incidence and molecular regulation of BS.