Research On The Relationship Between Chilling Injury Formation And Sugar Metabolism In Postharvest Peach Fruit

Low temperature storage is a practical method to extend the shelf life of peach fruit.However,peach fruit is a cold-sensitive fruit and is susceptible to chilling injury（CI）under low temperature environment,which seriously affects its quality and commercial value.Therefore,it is of great theoretical and practical significance to study the mechanism of CI formation and to explore corresponding control techniques.It has been shown that soluble sugars in peach fruit are in a dynamic equilibrium,and higher sucrose concentration can improve the cold resistance of peach fruit.However,the molecular mechanisms by which sugar metabolism affects CI formation are not clear and need to be further elucidated.1-methylcyclopropene（1-MCP）and methyl jasmonate（Me JA）are potential postharvest treatments that have been shown to delay CI formation in peach fruit,both of which involve the regulation of sugar metabolism.In this study,we firstly compared the effect of 1-MCP and Me JA treatments on the inhibition of CI in peach fruit,which indicated that sugar metabolism was closely related to CI formation in peach fruit.In order to further explore the key factors involved in the regulation of CI formation in sugar metabolism,we investigated the differences in CI formation and sugar metabolism in peach fruit with different sugar concentration under low temperature stress.Additionally,we screened the potential regulatory factors related to CI formation in the sugar metabolism pathway based on transcriptomic sequencing（RNA-Seq）and weighted co-expression network analysis（WGCNA）.Furthermore,yeast one-hybrid（Y1H）is used to investigate the potential regulatory factors related to CI formation in sugar metabolism.The main results are as follows:（1）In this study,the effects of 10μmol L^-11-MCP and 10μmol L^-1Me JA treatments on peach fruit were evaluated.The results showed that both treatments could regulate sucrose metabolism and energy metabolism to delay CI formation in peach fruit during low temperature storage.However,there were differences in the mechanisms of action of the two treatments to inhibit the formation of CI in peach fruit.1-MCP treatment was found to be more effective in modulating energy metabolic pathways by increasing adenosine triphosphate（ATP）concentration,energy charge（EC）level.In contrast,Me JA treatment had a more significant regulatory effect on sucrose metabolism,activating the sucrose synthesis pathway at the enzyme activity and transcriptional levels,while inhibiting the sucrose degradation pathway,resulting in sucrose accumulation and the alleviation of CI development.（2）In this study,we analyzed the correlation between CI formation and soluble sugar concentration in peach fruit with different sugar concentrations（high-sugar,medium-sugar,and low-sugar）during low temperature storage.We found that 21 d and 28 d were the critical time points for CI formation,and the CI index was negatively correlated with sucrose concentration,with high-sugar peach fruit showing significantly lower rates of CI formation than medium-and low-sugar peach fruit.Transcriptomic analysis was performed on high-sugar and low-sugar peach fruit at 0,21,and 28 days,and a total of 3920 differentially expressed genes（DEGs）were identified.The 3920 DEGs were analyzed by WGCNA,and the"MEpink"module was found to be significantly and positively correlated with sucrose concentration.1468 DEGs in the"MEpink"module was further analyzed,and five key genes（Pp SS,Pp MGAM,Pp INV,Pp FRK and Pp HXK）involved in sugar metabolism.Through co-expression network maps and regulatory element prediction,eight TFs（Pp MYB1/3,Pp MYB-related1,Pp WRKY4,Ppb ZIP1/2/3,and Ppb HLH2）were identified as having potential interactions with the five functional genes,providing insights into the transcriptional regulation of the five functional genes in sugar metabolism affecting CI formation in peach fruit.（3）Based on the results of the previous transcriptomic analysis,we focused on the key functional genes Pp MGAM,Pp INV,Pp FRK and Pp HXK in the sucrose and hexose metabolic pathways,and explored the TFs involved in regulating their transcriptional activities by Y1H.Our results indicated that Pp MYB3,Pp MYB-related1 and Ppb ZIP1/2/3 could bind to the promoter of Pp MGAM,might attribute to regulating the degradation of sucrose.Ppb ZIP1/2/3could bind to the promoter of Pp HXK,and Ppb ZIP3 could bind to the promoter of Pp FRK,which might help to regulate the phosphorylation of hexose.Ppb ZIP3 was found to be a common upstream regulator of all three genes.Therefore,we focused on the bioinformatic prediction of the protein sequences of Ppb ZIP1,Ppb ZIP2 and Ppb ZIP3.We constructed a phylogenetic tree by comparing the three b ZIP family genes with Arabidopsis b ZIP family genes,and the results showed that Ppb ZIP1,Ppb ZIP2 and Ppb ZIP3 in peach fruit were closely related to Atb ZIP1 and Atb ZIP53 in Arabidopsis,suggesting possible functional similarities that require further investigation.