| Peach(Prunus persica L.)belongs to the Rosaceae family,subfamily Prunoideae.Peach originated in China,where it produces abundant of peach landraces,which have been self-fruited during adaptation to local ecological environment,resulting in formation of huge landraces groups.According to geographical and ecological conditions and biological characteristics,these natural populations can be classified into seven groups.Peach accessions,grown in these groups,have typical regional characteristics and strong environmental adaptability,and contain many valuable genes that are easier to use,which is the foundation of breeding excellent varieties.All these are the major information sources for breeding excellent varieties,and in order to apply them fully in peach breeding,it is needful to assemble a genome for a typical landrace of each group.In addition,the genomic variation of Pp BL is still unclear.In our study,we present a high-quality genome of an blood fleshed landrace Tianjin Shui Mi(referred to TJSM),which belongs to North Plain China group and is an influential germplasm in modern peach breeding.We then perform a gene families clustering analysis among eight species genomes and conduct variation identification based on alignment of four genomes(TJSM,Chinese Cling,LHSM and RYP1)with reference genome ‘Lovell’.We also track the characteristic of LTR-RTs in TJSM genome,and further explore the mechanism of6688 bp LTR-RT(referred to blood-TE)in blood flesh formation and forword shift in fruit maturity date.In addition,in order to reveal the regulation effect of sugar signals on key genes of anthocyanin,we mainly focused on how different sugars induce anthocyanins accumulation in peach fruit flesh.1.The assembled genome ‘TJSM’ contained 243.5Mb megabases with a contig N50 of23.7Mb.97.57% of the total assembled genome(237.63Mb)was anchored on eight pseudo-chromosomes.Compared with eight plant species,78 gene families were found to expanded significantly in TJSM genome(p-value=0.05).And 912 gene families were found to contracted significantly in TJSM genome(p-value=0.05).Comparing with other there peach genomes(Chinese Cling,LHSM and RYP1),TJSM had the largest number of specific SVs.The genes with these SVs distribution were enriched into stress-related metabolic pathways,among which two genes belong to anthocyanin synthesis pathway.Comparing with other four genomes reported,TJSM also had the largest number of LTR-RTs.These LTR-RTs were classified into five types according to the diversity(%).Different type of LTR-RTs had the tendency to insert into the genes with different function.Among these affected genes,two are structural and regulatory genes of the anthocyanin pathway.2.Among the four anthocyanin pathway genes carrying SV and LTR-RT,one is the main blood flesh gene Pp BL,which has the blood-TE on its promoter.The blood-TE was not only a key factor responsible for blood-flesh trait,and but also worked together with other two variations(a transposon and a deletion)to determine the formation of different intensities of the blood-flesh color.The sequence between-653 to-4450 bp was the major promoter region that results in low level expression of Pp BL.Afterward,a WRKY70 like gene,designated as Pp WRKY70,was identified using the 497 bp sequence,and was validated to have repressive activity to promoter of Pp BL in tobacco leaf.3.Peach plants with the blood-TE showed the forward shift in fruit maturity date,such as the fruits with late-maturity genotype Prupe.4G186800(0bp/0bp)displayed intermediate-maturity phenotype,similarly,the fruits with intermediate-maturity genotype Prupe.4G186800(0bp/9bp)showed early-maturity phenotype.Pp BL is a positive regulator of ethylene biosynthesis,and the corresponding effect is stronger than the Prupe.4G186800(no9bp insertion)in up-regulating the expression of Pp ACO1 and Pp ACS1.4.Glucose,sucrose,sorbitol,and fructose all had similar effects on metabolite accumulation in vitro.After four sugars treatment for 12 and 24 h,anthocyanins were accumulated as cyanidin-3-O-(6-O-p-coumaroyl)glucoside.Two key structural genes of the anthocyanin biosynthesis pathway,namely,Pp DFR and Pp UFGT,were upregulated in the flesh of sugar-treated peach fruit.By contrast,the two main transcription factors(TFs)Pp MYB10.1 and Pp BL regulating anthocyanin biosynthetic genes in peach fruit were not upregulated accordingly.Interestingly,two MYB family genes(Pp MYB6 and Pp MYB44-like)and three b HLH family genes(Ppb HLH35,Ppb HLH51,and Ppb HLH36-like)were upregulated.A dual luciferase assay revealed that Pp MYB6 strongly activated the Pp UFGT promoter when it was co-infiltrated with Ppb HLH35,Ppb HLH51,and Ppb HLH36-like.When Pp MYB44-like was co-infiltrated with Ppb HLH35,it also potently activated the Pp UFGT promoter. |
