Effect Of Cooling Speeds On Browning Of Yali Pear Core And Mining Of Related Genes

‘Yali’ pear（Pyrus bretschneideri Rehd cv.Yali）is the one of the earliest export commodities in China.It has refreshing taste and its effect of refreshing heat and nourishing the lungs.However,it is prone to adversity damage during storage and transportation,resulting in the browning of core,which severely restricts the development of China’s pear industry.Based on the results of previous studies,this experiment explored the browning mechanism of ‘Yali’ pear in more depth.In this study,three maturity Yali pears were respectively treated with rapid and slow cooling to determine the changes in physiological indicators such as hardness,SSC content,and respiratory intensity during storage,and to observe and count the browning of the‘Yali’ pear core.The browning-related genes were screened by transcriptome sequencing technology,and the regulation of browning genes was analyzed to verify the browning mechanism of ‘Yali’ pear core.The main results are as follows:1.The higher the maturity,the more severe the browning of the ‘Yali’ pear core.Compared with the rapid cooling treatment,the slow cooling treatment inhibited the occurrence of early and middle harvest ‘Yali’ pear core browning.The situation of late-harvested “Yali’ pear was just the opposite.The slow cooling and late-harvested‘Yali’ pear browned earliest.The respiratory intensity and peak respiratory value of early and middle harvest ‘Yali’ pear under slow cooling were lower than those of rapid cooling,and the hardness and SSC content decreased slowly.The marketable fruit rate after storage was respectively higher,and the marketable fruit rate of early-harvested and middle-harvested ‘Yali’ pears was 89.2% and 91.7%.2.A total of 103.42 G Clean date was obtained by RNA-seq technology,Q30 was greater than 90%,GC content was between 40%-60%,the overall data sequencing error rate was 0.03%,and the comparison rate of each sample to the reference gene was greater than 68 %.The quality of sequencing data was high.The GO gene enrichment analysis of the differential genes found that the browning-related genes of‘Yali’ pear core were mainly concentrated in biological processes and molecular functions,focusing on defense responses,lipid metabolism and transcription factor activity.KEGG metabolism was mainly concentrated on several pathways such as aspartic acid,alanine and glutamic acid metabolism,phenylpropane metabolism,plant hormone signaling,arginine and proline metabolism,and plant MAPK signal transduction pathway.Through comprehensive analysised and screened,arginine decarboxylase（ADC）,dehydration 3（DHN3）,aspartic protease（AP）,WRKY31 transcription factor,laccase 15（LAC15）and peroxidase 42（POD42）genes,which six genes related to browning,were finally selected for subsequent quantitative analysis.3.Quantitative analysis of the six genes screened by RT-PCR found that the expression of ADC,AP,DHN3,and transcription factor WRKY31 increased first and then decreased,and the expression of POD42 continued to down-regulate during storage.The slow cooling could inhibit the decline gene expression of ADC,AP,DHN3 and transcription factor WRKY31 in early and middle-harvested ‘Yali’ pear,which indicated that slow cooling could increase the cold tolerance of its.And the middle-harvested ‘Yali’ pear under slow cooling had high SSC content and POD activity,inhibited the time of respiratory climacteric,and its antioxidant activity was strong.Therefore,its core browning degree was lightest.This ADC,AP,DHN3 and transcription factor WRKY31 were also up-regulated in the late-harvested ‘Yali’ pear during the early storage period,but the expression level was low.Furthermore,due to the slow cooling for a long time,the fruit had high respiration intensity,accelerated senescence,and then the late-harvested ‘Yali’ pear was subjected to cold stress and accompanied by the accelerated senescence of the fruits,which led to the earliest occurrence of browning.The rapid cooling treatment promoted the up-regulated expression of LAC15 in early and middle-harvested ‘Yali’ pear,and promoted the occurrence of browning.The expression of LAC15 in the late-harvested of ‘Yali’ pear was lower,which indicated that its browning in the early storage had little relationship with LAC15.