Preservation Of Fresh-cut Papaya And Study Of Papaya Senescence-associated Genes

Papaya(Carica papaya L.)is one of the most important fruit crops cultivated in tropical and sub-tropical areas and the ripe fhuit has a delicious taste with high amounts of sugar,organic acid,protein,fat,vitamins,soluble calcium,iron and other nutrients.Nowadays,the pace of life has become faster and people’s living standards have been improved remarkably.Researchers and consumers are becoming more aware of the importance of fresh-cut fruits.However,the mechanical damage of fresh-cut fruits may lead to rapid activation of respiratory and metabolic responses,and rapid decline in fruit quality.In addition,because papaya is a typical climacteric fruit,it ripens very quickly with striking color changes,substantial pulp softening,and rotting after harvesting.One of the major problems faced by the global papaya industry is significant post-harvest losses throughout the marketing chain.Therefore,fresh-cut papaya fruit preservation technology were studied,ripening-related candidate genes of papaya fruits were isolated,a senescence associated gene(SAG)was cloned,and an overexpression vector of viMDC140-CpSAG was constructed and transformed into Agrobacterium.The major results obtained from the study are summarized as follow:1.The fresh-cut papaya fleshes were treated with different preservatives respectively.Compared with the control,preservative treatments effectively maintained the fresh color and high level of Vc content,reduced the weight loss of fruit,delayed the fruit softening and aging.Among all the treatments,CC3(0.1%cinnamaldehyde+1%calcium chloride)was selected as the best preserver and extended the shelf-life of seven days for fresh-cut papaya preservation at 8 C.2.A total of eighteen fruit ripening-related genes were isolated from ethylene/1-MCP treated papaya through RNA-seq.There were six cell wall-related genes(XTHSO,GLU-B,PL,EGase,EXPA,PMIS),three chlorophyll and carotenoid metabolism-related genes(CHY-B,CHLM,FER1),three proteinases and their inhibitors(AIR,CPSP,SERPIN),four plant hormone signal transduction pathway genes(ERS,EBF2,HAB1,GH3.1)one NAC transcription factors,and one senescence-associated gene(SAG).The expression profiles of sixteen candidate genes determining using semi-quantitative RT-PCR data were consistent with the RNA-seq results,thus confirming our transcriptome analysis.Transcription levels of six selected genes(XTH30,GLUB41,PL,PMIS｛CPSP,CHLM)were measured by RT-qPCR.The results verified that the expression pattern of the six genes is consistent with the fruit senescence process.These findings strongly suggest that these genes may be involved in the ripening of papaya fruit.3.A full-length cDNA clone encoding CpSAG was cloned from papaya,the opening reading frame of the gene is 879 bp,encoding a protein with 292 amino acids.Bioinformatics analysis showed that the protein is an unstable transmembrane protein with one signal peptide.And the protein of CpSAG contains a region of two transmembrane helices,it may be involved in sugar efflux transporter for intercellular exchange.Phylogenetic analysis indicated that CpSAG has a closest relationship with tobacco senescence-related gene.Finally,a plant overexpression vector of pMDC 140-CpSA G was constructed using In-Fusion technology.