Physiological Basis Of Fruit Softening And Mining Of Breeding-Usable Genes From "Slow-Melting" Peach

Peach(Prunus persica L.)is one of the main deciduous fruit tree species in China.The ripening period of peach is mainly in the summer with high temperature in China,fruit is quickly softened after the harvest.Poor storage and transportation are the key factors restricting the healthy development of peach industry.Slow melting varieties has the characteristics of long fruiting period,good storage,which is the idea type of breeding germplasm.In this study,we explored the genetic mechanism and elite gene mining of the slow melting peach from the aspects of physiology,molecular biology and bioinformatics,and also carry out the slow melting peach breeding.The main results are as follows:1.Analysis of softening mechanism and metabolic characteristics of slow melting peach.By analyzing the changes of pectin components and cellulose components of slow melting and its control flesh type after harvest,the covalently soluble pectin(CSP)content of slow melting variety is higher than that of soft melting type.Although its content decreases slowly after harvest,it has maintained a high level,which is conducive to the maintenance of fruit firmness.By analyzing the physiological and gene expression differences between slow melting and control fruits during tree hanging period,it was found that the reason for the long tree hanging period of slow melting varieties was more directly related to the inhibition of the expression of Pp PG gene,and indirectly related to the inhibition of the expression of maturity related genes Pp ACS1 、 Pp ACO1 and Pp YUC11.The contents of zeatin,flavonoids such as geranium 3-glucoside in slow melting varieties were higher than those in soft melting varieties.The results clarify the physiological and gene differential expression mechanism and metabolic differences of slow melting peach softening,which provides a reference for post harvest treatment and further excavation the key locus which control slow melting trait.2.Genetic mapping and gene mining of slow melting traits in peach.By using a cross population of ‘Spring Snow’ and ‘Hongburuan’ to determine the candidate genes related to the slow melting process,using the methods of bulked segregant analysis(BSA)analysis,the QTLs of slow melting traits were located on chromosome 4,its position between 4,365,348～ 6,365,348 bp and 6,534,086 ～ 10,181,052 bp.By integrating the results of comparative transcriptome analysis,a total of 29 differentially expressed genes were identified.The identified differentially expressed genes and GO analysis results showed that,the pectin lyase gene Prupe.4G116400,auxin early response gene Prupe.4G136800 and gibberellin 2-beta-dioxygenase Prupe.4G150200 may be involved in the peach softening process.Through the analysis of differential gene expression of peach slow melting germplasm when the fruit is close to maturity,only 25 genes of 29 differential genes related to slow melting were expressed during fruit ripening of 27 peach germplasm.The expression of pectin lyase gene Prupe.4G116400 in slow melting type was significantly lower than that in soft melting type.Prupe.4G116400 gene was preliminarily identified as a candidate gene for slow melting trait.3.Marker development and breeding utilization of slow melting candidate genes in peach.Analyze the sequence differences including the promoter of Prupe.4G116400 gene,three variation sites were found.Detected with mutation sites,the identification accuracy of slow melting germplasm was 78% in natural population and 71% in hybrid offspring.A batch of slow melting germplasm with consistent genotype and phenotype were identified.By preparing the hybrid crosses of slow melting varieties,more than 10 excellent lines of slow melting were obtained,and two varieties ‘Zhongyoupan 9’ and ‘Zhongpantao 11’were identified to contain the genotype corresponding to the Prupe.4G116400 gene,The results provide reference for the subsequent identification of slow melting germplasm,and provide theoretical support for the breeding of new slow melting peach varieties.In conclusion,through the physiological and gene expression analysis of slow melting peach and the identification and screening of candidate genes,this study identified the expression differences of key physiological and maturity related genes in the softening process of slow melting peach.Finally,the pectin lyase gene prupe.4G116400 was determined as the candidate gene controlling slow melting trait.The sequence differences of the gene were analyzed,and the genetic variation loci that could be used for the identification of slow melting peach germplasm were found.New lines of slow melting peach were selected,and the research results laid a foundation for further research of slow melting peach.