Identification And Functional Characterization Of Regulatory Genes Of Organic Acid Accumulation In Peach

One of the important factors affecting fruit taste was the content and composition of organic acids.Regulating the organic acid content of fruit to meet the needs of different consumers is one of the important goals of fruit breeding.The organic acids in peach fruit mainly consist of malic acid,citric acid and quinic acid.In peach,the genetic mapping and molecular marker of taste evaluation(non-acid/acid),pH value,titratable acid and organic acid components have been reported.Previous studies have found that the organic acid content of peach fruit is controlled by multiple genes.Although genes associated with peach acid content have been reported,the key genes and the mutated alleles in the major quantitative trait loci(QTL)located at the top of chromosome 5 have not been well studied.Therefore,it is of great significance to identify key genes and the mutated alleles by various approaches and underly the regulatory mechanism of organic acid accumulation,which will facilitate the improvement of peach fruit flavor.The following are the main results:1.Genetic mapping of organic acid content.Genome-wide association analysis showed that the region range from 0.63 to 1.48 Mb on the top of chromosome 5 was considered as the candidate interval.BSA showed that the most significant locus was 0.47～0.83 Mb at the top of chromosome 5.The region from 0.47 to 1.48 Mb on the top of chromosome 5 was identified as the key interval for total organic acid accumulation.2.Identification and functional analysis of key genes regulating acid accumulation.The dynamic change trend of organic acid contents in 4 peach accessions during six developmental stages was detected.Combined with transcriptome analysis,the 1470 DEGs related to the change of organic acid content were identified.Based on the above results,three candidate genes were obtained.Transient overexpression of the three genes revealed only overexpression of PpTSTl had significant effect on the accumulation of total organic acid and the TA value.The genotype of PpTST1 with a single-base transversion(G1584T)in the third exon which leads to a single amino acid substitution(Q528H)was associated with low level of organic acid content in peach.Overexpression of PpTST1His resulted in reduced organic acid content along with increased sugar content both in peach and tomato fruits.The frequency of three genotypes in wild,landrace and improved groups and geographical distribution of genotypes were analyzed,indicating that PpTST1 was strongly positively selected during peach evolution,which was consistent with human selection of fruit flavor and taste substances.3.Illustration of genes involved in regulating malic and citric acid.Three candidate genes were identified by WGCNA for the regulation of malic acid content in peach,two of which encode transcription factors WRKY50 and MYB62,and the other encode cation/H+exchanger.A candidate gene encoding transcription factor bHLHl was found to regulate citric acid content in peach.In this study,PpTST1 was identified as the key gene for organic acid accumulation in peach by multi-omics approaches.A single-base transversion(G1584T)in PpTST1 might be responsible for organic acid reduction.Three genes and one gene were detected as the candidate genes for malic acid and citric acid,respectively.