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

�Nanguo' pears(Pyrus ussuriensis Maxim.)are climacteric fruit,native to Liaoning province,China.They are normally harvested in early September,refrigeration is a common technique used to extend the fruit supply.However,with low-temperature storage,the proper aroma of the pear is lost when it matures during shelf-life at room temperature,which is a serious problem.Precious research in our laboratory found that the content of the aroma-related esters of fruit after refrigeration was significantly lower than fruit ripening at room temperature.1-Methylcyclopropene(1-MCP),which binds to ethylene receptors,is an effective ethylene-antagonising compound and is used to prolong the storability of various fruit.But researches show that 1-MCP inhibited the production of total volatiles,especially ester of fruit.And the content of aroma-related esters could be improved by ethephon treatment after cold storage.The above research results show that ethylene plays a vital role in the formation of fruit aroma,but till now the molecular mechanism on synthesis of aroma-related esters of Nanguo pears regulated by ethylene is not clear.In this study,we investigated the the effect of cold storage on key genes involved in ethylene biosynthetic and signal transduction of �Nanguo' pears based on RNA-seq analysis,and the effect of cold storage on the aroma-related esters and its synthesis enzyme activities and gene expression were analyzed at the sametime.Furthermore,exogenous ethylene and ethylene absorbents were further use to verify the role of the ethylene in the synthesis of aroma-related esters of �Nanguo' pears and discuss the recovery of aroma-related esters after treatment with exogenous ethylene.The main results of this study are following:(1)Compared with the fruits without refrigeration,the activities of ethylene biosynthesis-related enzymes,ethylene production,aroma production capacity,and aroma-related enzymes activities were reduced at the same maturity in fruits stored at 90 d and 150 d.Moreover,the longer the period of cold storage of �Nanguo' pears,the severer the degree of reduced aroma.We identified the key genes in the ethylene signal transduction pathway of Nanguo pears based on RNA-seq analysis,it was found that cold storage inhibited the activity of key enzymes and genes expression in the ethylene biosynthesis pathway,and PuETR,PuERS1,PuEIN3,PuCTR1 and PuEIN2 were repressed.These results reveled that the inhibitory effect of cold storage on aroma may be related to the low production of ethylene and expression of genes involved in ethylene biosynthesis and signal transduction.(2)Treatment of Nanguo pear with exogenous ethylene and ethylene absorbers showed differences in expression of different members of the LOX pathway gene family in the three groups of fruits,suggesting that their sensitivity to ethylene was different.We screened out several key genes that were significantly regulated by ethylene in the three groups: PuLOX6,PuLOX5,PuLOX1,PuADH3,PuAAT and PuHPL.(3)After cold storage for 90 days and at 150 days,exogenous ethylene treatment was applied at low temperature.It was found that exogenous ethylene treatment can increase the ethylene production and aroma generation ability of refrigerated fruits to a certain extent,which has a certain effect on the refrigerated Nanguo pear aroma quality.In exogenous ethylene-treated fruits,the expressions of PuLOX1,PuAAT1,PuADH3 and PuHPL genes were significantly increased,indicating that for the refrigerated Nanguo pear fruits,ethylene was mainly up-regulated these genes in the LOX pathway to alleviate the damage caused by cold storage on aroma-related esters.