Mechanisms For Differential Accumulation Of Anthocyanin In Peel Of Two Peach Cultivars And The Regulation By Light

Red coloration is an essential trait of maturity and quality for peach(Prunus persica)fruit,which is mainly determined by anthocyanin content.Light is a critical environmental factor for anthocyanin biosynthesis.In our study.’Hujingmilu’(’HJ’),a naturally deeply colored cultivar.and ’Yulu’(’YL’),a naturally barely colored cultivar,were used to study the mechanism underlying light-induced anthocyanin biosynthesis and differential sensitivity of fruit pigmentation to ultraviolet light.The main results were shown as follows:1.The peach cultivar’HJ’can accumulate anthocyanin in pericarp throughout fruit development and ripening.Another peach cultivar’YL’barely accumulates anthocyanin but produces higher content of total flavonoids compared to that of ’HJ’.To explore whether the ability of anthocyanin accumulation in two peach cultivars was caused by the differences in related gene sequences,we performed SNP prediction based on RNA-seq data under a comprehensive comparison of tvwo paired-end read lengths(125 bp and 150 bp),five assemblers(Trinity,IDBA,oases,SOAPdenovo,Trans-abyss)and two SNP callers(GATK and GBS).Putative SNPs predicted from the same RNA-seq data with different strategies led to quite divergent results.The combination of assembler Trinity,SNP caller GATK,and the paired-end read length 150 bp had the best performance in SNP discovery with 100%accuracy both in peach.In two cultivars,a total of 40 authentic SNPs were identified in five anthocyanin biosynthesis related genes,among them only UFGT was found to differ in 2 amino acid residues due to the SNP.2.A phi(F)class glutathione transferase PpGST1 was identified and characterized as an anthocyanin-related GST from peach.Expression analysis demonstrated that the transcript profiles of PpGSTl were tissue-affected and cultivar specific and strongly associated with anthocyanin hyper-accumulation in peach.Functional complementation analysis of PpGST1 in the Arabidopsis transparent testa 19(tt19)mutant and transient overexpression in tobacco leaves and peach fruit indicated PpGSTl was involved in anthocyanin transport and did not function in proanthocyanidins accumulation.Moreover,virus-induced gene silencing of PpGST1 resulted in a distinct reduction in anthocyanin pigmentation in blood-fleshed peach.PpMYB10.1,a positive R2R3-MYB transcription factor,not only regulated anthocyanin biosynthesis,but also participated in anthocyanin transport through activating the transcription of PpGST1.3.Two cultivars showed differential sensitivity to different light qualities.Both UVB and UVA induced fruit pigmentation of ’HJ’,but’YL’ was only sensitive to UVB.Transcriptomic analyses showed the expression levels of anthocyanin biosynthetic structural genes were consistent with anthocyanin accumulation.Several light receptors(PpUVR8.1 and PpCRYl),light signal transduction related genes(PpCOP1.1,PpCOP10 and PpHY5,PpHYH)and a specific anthocyanin transporter glutathione S-transferase(PpGST1)were responsible for the differential UV-light sensitivities of two cultivars.Expression profiles of several transcription factors of the families MYB,bHLH,bZIP and NAC were highly correlated with those of the anthocyanin biosynthesis genes,which might participate in UV-light-induced anthocyanin biosynthesis in peach.4.The molecular mechanisms of UVB and UVA induced anthocyanin response were further investigated.Functional complementation analysis in Arabidopsis mutant and UV treatment experiments suggested that the light receptors PpUVR8.1 and PpCRYl could regulate anthocyanin biosynthesis.PpHY5 was involved in both UVB and UVA light-controlled anthocyanin accumulation,which was depended on PpUVR8.1 and PpCRY1,respectively.PpHY5 could positively regulate its own transcription and trans-activate the promoters of anthocyanin biosynthesis related genes(PpCHS,PpDFR,PpMYB10.1)by recognizing the G-box and ACGT-containing element(ACE).PpHYH,a homologous gene of PpHY5.might perform the similar function in UV-light-induced anthocyanin biosynthesis.