Molecular Mechanism Of The Effect Of Methyl Jasmonate On Aroma-related Esters Of Cold Storage Nanguo Pears

�Nanguo' pear belongs to Pyrus ussuriensis Maxim.,and is a typical climacteric fruit.Refrigeration is often used in production to extend the fruit storage period.However,�Nanguo' pears are prone to chilling damage after refrigeration,so that the aroma is lightened.The previous research in our laboratory found that cold storage will significantly reduce the content of aroma-related esters in �Nanguo' pears.Application of exogenous ethylene treatment in �Nanguo' pears before being moved from refrigeration can increase the aroma content after refrigerated storage and researching the mechanism of action from the signal transduction pathway of ethylene.The results showed that the biosynthesis of aroma-related esters was closely related to the biosynthesis and signal transduction of ethylene.Methyl jasmonate(Me JA)is a widely used plant hormone.Previous studies have shown that Me JA can promote the production of volatile substances in the process of fruit ripening,stimulate the jasmonic acid signal transduction pathway and has a positive effect on plants under cold stress.Therefore,this study analyzed the effects of refrigeration on the activity and gene expression of the key enzyme in the synthesis of aroma-related esters,and screened out the better Me JA concentration that was relatively good for the activity and gene expression of the key enzyme in the synthesis of aroma-related esters after refrigeration.The optimal concentration of Me JA was selected to treat �Nanguo' pears,and the effects of Me JA on the synthesis and signal transduction of ethylene and jasmonic acid were studied to investigate the regulation of Me JA on ester aroma after refrigeration.In order to obtain the effective control means of reducing the aroma of refrigerated �Nanguo' pears.The main results of the study are as follows:(1)When refrigerated fruits are transferred to room temperature shelves and matured to the same maturity of unrefrigerated fruits,the type and content of aroma-related esters are significantly reduced,and the longer the refrigerating time,the more significant the aroma decreases.The total ester content decreased by 27.11% and 44.30% respectively after refrigerating 90 d and 150 d in the OTP.The activities of ADH and AAT,the key enzymes in the ester synthesis pathway,were significantly reduced after refrigeration.The expression of Pu LOX5?Pu ADH3 and Pu AAT1 were inhibited,which indicates that refrigeration decresed the aroma of �Nanguo' pears by affecting the key enzymes of the ester synthesis pathway and their gene expression.(2)The three treatments of 50,100 and 200?mol/L Me JA had different promoting effects on the aroma,the key enzyme activity and the gene expression of Nanguo pears.When treated with 100?mol/L Me JA,aroma-related esters types and contents were significantly improved,and the increase of total ester content in the OTP was 1.15 and 1.1 times of that in the 50 and200?mol/L groups,respectively.The activity of ADH and AAT and the expression of Pu LOX5?Pu ADH3 and Pu AAT1 in 100?mol/L Me JA-treated fruits were better than the other two treatments.Therefore,100?mol/L Me JA is the optimal treatment for �Nanguo' pears.(3)Me JA significantly increased the aroma content of �Nanguo' pears esters in OTP after cold storage.The activities of ADH and AAT were significantly increased by Me JA.After analyzing the expression levels of six key genes in the ester aroma synthesis pathway,Me JA has a positive effect on the aroma of fruits by increasing the expression levels of Pu LOX5?Pu ADH3?Pu AAT1 and Pu HPL during the OTP.Me JA significantly increased ethylene production of Nanguo pears after cold storage,and played a positive role in regulating the key ethylene synthesis enzymes ACS,ACO and its key genes Pu ACS1 and Pu ACO1.Four genes were inhibited by refrigeration,which were Pu ERS1?Pu EIN4?Pu EIN2 and Pu ERF1,and the expresstion of these genes were significantly up-regulated by Me JA.In addition,Pu ETR1 showed an obvious peak under the action of Me JA.This indicates that Me JA has a promotion effect on the ethylene pathway which were related to the fruit aroma synthesis and inhibited by refrigerated storage,and regulates ester aroma synthesis of Nanguo pears by promoting the above enzyme activities and gene expression levels.The content of endogenous jasmonic acid in fruits increased after cold storage,and the expression of three jasmonic acid synthesis genes,Pu AOS ? Pu AOC4 and Pu OPR3,was up-regulated after cold storage,and the longer the time of cold storage was,the more obvious it was.After the application of Me JA,the expression of these three genes can be significantly stimulated,and it is more obvious in long-term refrigerated fruits.The expression of Pu JAR1?Pu COI1 and Pu MYC2 was increased after short-term refrigeration,but the effect was not obvious.It's significant after long-term refrigeration.Pu JAZ9 was significantly increased in the early period after long-term refrigeration.Me JA significantly stimulated the Pu JAR1,Pu COI1 and Pu MYC2,which can up-regulated the expression of these genes.It shows that Me JA can improve the defense transduction signal of jasmonic acid by changing the expression of the above key genes to cope with cold stress,thereby reducing the inhibitory effect of refrigeration on aroma-related esters.