Mechanism Study Of 1-methyl Cyclopropene Treatment On Inhibiting Chilling Injury In Postharvest Peach Fruit

Peach fruit（Prunus persica L.）is highly valued for its nutritional content and delicious taste,its storage period is short at room temperature and mostly stored at low-temperature.However,peach fruit are susceptible to chilling injury（CI）during long-term low-temperature storage,which reduces its commercial value.Therefore,there is an urgent need to find an effective postharvest treatment to inhibit the formation of CI in peach fruit.1-Methylcyclopropene（1-MCP）,an ethylene inhibitor,has been shown to alleviate CI symptoms in peach fruit,but the molecular mechanisms underlying this regulation are not well understood and need to be further investigated.In this study,"Hujingmilu"peach fruit were used as the experimental material,we investigated the effects of different concentrations of 1-MCP on CI symptoms in peach fruit and identified the optimal treatment concentration.Transcriptomic analysis was used to identify the key regulatory pathways of 1-MCP in inhibiting CI formation.To further explore the relationship between 1-MCP treatment and the regulation of cell wall pectin metabolism,IAA biosynthesis,auxin signal transduction pathways,and CI formation during storage of peach fruit.The main results are as follows:（1）Different concentrations(1,10,and 50μl·L^-1)of 1-MCP treatments reduced CI index,firmness,decay rate,respiration rate,ethylene production,relative electrolyte leakage,and malondialdehyde（MDA）concentration of peach fruit during storage,while maintaining vitamin C concentration.However,no significant differences were observed in the regulation of soluble solid（SSC）and titratable acid（TA）.Notably,the 10 and 50μl·L^-1 1-MCP treatment groups had a more significant inhibitory effect on peach fruit CI,but the decay rate of the 50μl·L^-1 1-MCP treatment group was significantly higher than that of the 10μl·L^-1 1-MCP treatment group.Therefore,the concentration of 10μl·L^-1 1-MCP treatment was selected for further study.（2）Transcriptomic analysis was performed at four different time points,including CK 14d,10μl L^-1 1-MCP 14 d,CK 21 d,and 10μl L^-1 1-MCP 21 d.The two comparison groups（CK14 vs 1-MCP 14,CK 21 vs 1-MCP 21）revealed 708 and 1276 differentially expressed genes（DEGs）,respectively.This findings suggests that 1-MCP treatment significantly regulated a range of metabolic pathways in peach fruit during low-temperature storage.Through enrichment analysis of the Kyoto Encyclopedia of Genes and Genomes（KEGG）metabolic pathway,it was observed that the auxin signaling pathway,cell wall pectin metabolism,and indole pyruvate（IPy A）pathways were significantly responsive to 1-MCP-induced,suggesting a possible key metabolic pathway involved in the regulation of CI formation by 1-MCP treatment.（3）The experimental data showed that 10μl·L^-1 1-MCP treatment effectively maintained the structural integrity of the cell wall in peach fruit during storage by delaying the increase of water-soluble pectin（WSP）concentration,the decrease of water-insoluble pectin（WIP）,CDTA-soluble pectin（CSP）and sodium carbonate-soluble pectin（NSP）concentration.Correspondingly,1-MCP treatment also reduced the activities of polygalacturonase（PG）,pectin methylesterase（PME）and pectin lyase（PEL）,as well as the expression of Pp PG1,Pp PG2,Pp PME1,Pp PME2,Pp PEL1 and Pp PEL2.This indicates that 10μl·L^-11-MCP treatment alleviated peach fruit CI symptoms by inhibiting cell wall pectin degradation.（4）The results showed that 10μl·L^-1 1-MCP treatment reduced the activities of tryptophan transaminase（TAA）and flavin monooxygenase（YUCCA）as well as the expressions of key genes involved in IAA biosynthesis,such as Pp TAA1,Pp YUCCA1 and Pp YUCCA2 during storage,suggesting that 1-MCP treatment may lead to a reduction in endogenous indole-3-acetic acid（IAA）biosynthesis by regulating the IPy A pathway.Additionally,the expressions of Pp ARF1,Pp AUX/IAA1,Pp TIR1,Pp SAUR1,and Pp GH3-1 were down-regulated by 1-MCP treatment,indicating the inhibition of the auxin signaling pathway.Therefore,10μl·L^-11-MCP treatment improved cold tolerance of peach fruit by regulating the IPy A pathway and the auxin signaling pathway.In summary,the current study revealed that 1-MCP treatment was effective in preserving the structural integrity of the cell wall by regulating cell wall pectin metabolism.Additionally,1-MCP treatment resulted in the suppression of IAA biosynthesis through the inhibition of the IPy A pathway and the down-regulation of the auxin signaling pathway.These effects collectively contributed to the delayed onset of CI symptoms in peach fruit.