Analysis Of Lipid Metabolism In Strawberry Fruit Epidermi

Strawberry(Fragaria×ananassa Duch.)is a member of the Rosaceae family.Strawberry are widely welcomed by consumers with high nutritional value and delicious taste.The fruits of strawberry have high water content and thin skin,so they are easily damaged and rotten.Therefore,they are intolerant of storage and long transportation.Strawberry fruits can usually retain freshness for 1-2 days and can be stored for about a week at low temperatures.Study showed that fruit cuticle plays an important role in maintaining postharvest quality and delaying senescence,but there are few reports on strawberry cuticle.In this study,strawberry was selected as the research object.Researches were carried out in two aspects:chemical analysis of strawberry epidermal lipids and the expression of genes related to epidermal lipid metabolism.We selected five maturity stages of strawberry fruits(Small green stage T1,Large green stage T2,Large white stage T3,Red stage T4 and Full red stage T5)and fruits at harvest and stored at 4℃ for 7 days and 25 days to analyze the chemical components and contents of the fruit epidermis lipids.The expression changes of epidermal lipids metabolism-related genes after storage for different days were analyzed by transcriptome sequencing.The main results are as follows:The five mature stages(T1,T2,T3,T4 and T5)of "Shengdanhong" strawberry fruits were selected as the research objects.48 kinds of wax compounds were identified totally,including nine categories of alkanes,alkenes,fatty acids,primary alcohols,secondary alcohols,aldehydes,esters,others and undentified of which the dominant components were all alkanes.From T1 to T5,the content of total wax and nine major componentsd ecreased dramatically.In addition,18 cutin monomers were identified,which belonged to four major categories of fatty acids,hydroxy fatty acids,dicarboxylic acids and alcohols and the dominant components were all fatty acids.From T1 to T5,the content of total cutin and dicarboxylic acids increased significantly,the content of fatty acids and alcohols increased drastically,and the content of hydroxy fatty acids did not change significantly.The strawberry fruits of "Shengdanhong" and "Hongyan" at harvest and after storage for 7 days and 25 days at 4℃ were selected as the research objects.The changes of epidermal lipids components and content were determined.The results showed that the total wax content of the"Shengdanhong" fruits stored at 4℃ for 7 days did not change significantly compared with that at harvest time,the content of aldehydes increased significantly,and others significantly increased.After storage at 4℃ for 25 days,the content of total wax,and nine components were all significantly increased.The content of total cutin,dicarboxylic acids and hydroxy fatty acids were increased significantly after cold storage for 7 days compared with that at harvest.After storage for 25 days,the content of total cutin and alcohols were significantly reduced,and the content of fatty acids was extremely significantly reduced.For "Hongyan",the content of total wax and nine major components did not change significantly after 4℃ storage for 7 days compared with that at harvest.After cold storage for 25 days,total wax content,alkanes,alkenes and undentified increased significantly.After 7 days of cold storage,the total content of cutin monomers did not change significantly,the content of hydroxy fatty acids increased significantly,and the other components did not change significantly.There was no significant change in the content of total cutin monomers and four major components after 4℃ storage for 25 days compared with that at harvest.The changes of epidermal lipids chemical components in strawberry fruits during cold storage are mainly reflected in the changes of the content of dominant components.C29 alkanes are dominant components in wax,it can reduce the water loss rate of fruits during cold storage,and maintain the postharvest quality of strawberry fruits.The contents of C16 and C18 monomers related to dicarboxylic acids and hydroxy fatty acids in cutin monomers are closely related to the content of total cutin.These dominant components were beneficial to postharvest storage of strawberry fruits."Shengdanhong" strawberry fruits was selected for deep transcriptome sequencing through the BGI DNBSEQ platform.Differentially expressed genes involved in wax and cutin synthesis during cold storage were analyzed.16 genes were selected for qRT-PCR to the verification of transcriptome sequencing results.The chemical changes of epidermal lipids are closely related to the epidermal lipids metabolism related genes CER1,CYP94A5,LACS,CYP704B1,CYP86,etc.Combining the results of analytical chemistry with the results of transcriptome sequencing,it was found that the changes of lipids content such as hydroxy fatty acids,sterols,fatty acids and total wax in strawberry fruits epidermis during different time at cold storage were positively correlated with the changes of the expression of related genes.In this paper,the components and content of epidermal lipids in strawberry fruits at five mature stages and different time of low-temperature storage were analyzed.The chemical analysis and the expression of lipids metabolism related genes in strawberry fruits at cold storage for different days were revealed,which provided an important theoretical basis for the research on postharvest quality and fresh-keeping of strawberry fruits.