Genome-wide Association Study And Identification Of Candidate Genes Associated With Flower Color In Peach

Peach is one of the most important deciduous fruit trees in the world.Due to its small genome and low heterozygosity,it is considered as a model plant for genetic research of Rosaceae.Flower color is an important trait in peach and plays a crucial role in attracting pollinators,protects the reproductive organs of flowers from biotic and abiotic stresses,and assisting peach breeding by developing colorrelated markers in peach breeding programs.Molecular approaches to identify and modify flavonoid pathway genes are commonly used strategies in breeding to develop new flower colors in different plants.Flavonoids,particularly anthocyanins and flavonols,are the main pigments that determine the color of peach blossoms.In other model plants,the biosynthesis of these metabolites is directly or indirectly regulated by different structural and regulatory genes of the flavonoid biosynthetic pathway.It has been previously reported that the structure and regulatory genes of the anthocyanin biosynthesis pathway on chromosomes 3 and 4 of the peach genome are related to flower color.However,the exact molecular genetic mechanism underlying the formation of the peach color trait still largely remains unclear.· In the transcriptome analysis study using flowers which sampled in different development period,through weighted gene co-expression network analysis(WGCNA)a network of 15 hub genes that coexpressed throughout peach flower development was identified,including 5 genes encoded for the key enzymes(CHI,F3’H,DFR,LAR and UFGT)of flavonoid biosynthetic pathway and 1 gene Prupe.1G111700 identified as R2R3 family transcription factor MYB108.Over expression of PpMYB108 significantly increased anthocyanin biosynthesis in Nicotiana tobaccum flowers.Moreover,the expression correlation between PpMYB108 and PpDFR,suggests that PpMYB108 might play a role of transcriptional activator for PpDFR.This was further supported by transcriptional activation of PpDFR by PpMYB108 in yeast one-hybrid assay by binding to the promoter of DFR through a 6bp insertion of MYB biding site in its core promoter region.· For the first time a Genome-wide association study(GWAS)for flower color in peach was performed using 1508532 SNPs from 143 peach accessions grown as Zhengzhou Fruit Research Institute.Two QTLs associated with flower color were mapped on chromosome 1 of peach genome.Based on linkage disequilibrium 300 KB region around peak GWAS signals of both QTLs was narrowed down and 85 possible key candidates were identified.Then through the integration of GWAS results with comparative transcriptome analysis of red and pink flower peach cultivars 12 possible key candidates were identified.Based on functional annotation,gene expression analysis and correlation with flavonoids content,Flavonol Synthase(PpFLS1)gene of flavonoid biosynthetic pathway was identified as key candidates associated with most abundantly found pink color phenotypes of peach.A9 bp duplication insertion in the coding region of PpFLS1 was found associated with flower color.Moreover,PpFLS1 was found to be regulated by PpMYB6,an R2R3 family transcription factor,which is previously reported to activate several biosynthetic genes of flavonoid biosynthetic pathway in plants including peach.· This study provides the understanding of anthocyanin biosynthesis in peach flower and the role of associated network of previously reported structural genes of anthocyanin biosynthesis pathway as well as novel MYB and FLS gene that regulate the anthocyanin pathway in peach flower.These findings may be helpful in identifying anthocyanin related genes in other plant species.These findings will help the peach breeders in identifying cultivars by developing color associated markers in ornamental peach breeding.