Study Of The Regulatory Mechanism Of Light And Phytohormone In Anthocyanin Biosynthesis In Differently Colored Cherries (Prunus Avium L)

Anthocyanin accumulation level is one of the crucial factors affecting the appearance quality of sweet cherry(Prunus avium L)fruits.Based on the fruit color at the stage of ripeness,sweet cherries are classified into dark-red and bicolored cultivars,the peel of the bicolored fruits turn red when exposed to sunlight.Light is a particularly important environmental factor of anthocyanin biosynthesis.However,it is unclear to the roles and regulatory mechanisms of light on the accumulation of these pigments in different cultivars.In this study,the dark-red 'Hongdeng' and bicolored 'Rainier' were used as the materials to explore the potential roles of light on fruit coloring by bagging treatment.Moreover,RNA-Seq was applied to analyze the molecular mechanism of light regulating the coloring of sweet cherry fruits.In addition,Jasmonic acid(JA)is one of the important plant hormones,while it is unclear whether JA regulates the fruit coloring of sweet cherry fruits.Here we analyzed the potential role of JA signal in regulating pigment accumulation in 'Hongdeng'fruits.The main results have been achieved as followings:1.The bagging treatment showed that,compared with the normoal grown fruits,the peel and pulp of the bagged 33 dark-red cherries were colored despite the dark treatment;however,the bagged 11 bicolored cherries remained yellow.Additionally,the red coloration was consistent with the anthocyanin contents of the dark-red cultivar 'Hongdeng' and bicolored cultivar 'Rainier" fruits.Notably,anthocyanins were biosynthesized quickly in bagged 'Rainier' fruits after bag-removal.These data suggest that light is necessary for anthocyanin biosynthesis in bicolored cherries,but not in the dark-red fruits.2.Transcriptome data showed that genes encoding the anthocyanin biosynthesis enzymes chalcone synthase(CHS),chalcone isomerase(CHI),flavanone 3-hydroxylase(F3H),flavonoid 3'-hydroxylase(F3'H)and UDP-Glucose:flavonoid-3-O-glucosyltransferase(UFGT)were significantly upregulated by light in 'Rainier';but were not altered by light exposure in 'Hongdeng'.Meanwhile,the expression levels of 32 up-regulated and 40 down-regulated transcription factors were found to be significantly altered by light in the bicolored fruits.Besides,the expression levels of Phytochrome Interacting Factor 3(PIF3),Elongated Hypocotyl 5(HY5)and other transcription factors in the light signalling pathway,as well as key components of the hormonal signalling pathway,such as protein phosphatase 2Cs(PP2Cs),were regulated by light in the 'Rainier" fruits.A co-expression network analysis further revealed that abscisic acid(ABA)and gibberellic acid(GA)signaling pathways play important roles in light-dependent anthocyanin biosynthesis.4.Light and exogenous ABA co-treatment revealed that ABA promoted the anthocyanin accumulation of 'Hongdeng' fruits in both dark and light conditions.However,ABA could not increase the content of anthocyanin in 'Rainier' fruits under dark condition.The results above indicated that the different mechanisms of the synergistic regulation on the fruit coloration by light and ABA in these two sweet cherries.5.With the exogenous application of Me J A treatment,we found that MeJA can promote the anthocyanin accumulation in cherries,and increase the transcripts of anthocyanin biosynthetic structural genes PacDFR,PacANS,PacUFGT and transcription factor PacMYBA.Furthermore,6 PacJAZ genes of sweet cherry were obtained,and the protein sequence analysis showed that all of them had a TIFY domain and a Jas domain,belonging to different JAZ groups based on the sequence alignment with Arabidopsis JAZs.The expression heat map showed that the transcriptional levels of PacJAZs decreased gradually during the fruit development process.MeJA treatment can induce the expression levels of PacJAZ1?PacJAZ3?PacJAZ6?PacJAZ7 and PacJAZ10.In summary,the genes encoding key anthocyanin biosynthetic enzymes in differently colored cherries have different responses to the light signal.Light plays a major involvement in determining the pigment accumulation of the bicolored 'Rainier' cherries,but not in that of the dark-red 'Hongdeng' fruits.Furthermore,HY5 and PIF3 may play important roles in the light-dependent accumulation of anthocyanins by coordinating with ABA and GA signalling components to regulate the expression of anthocyanin biosynthetic transcription factors and structural genes.Besides,JA can accelerate the fruit coloring of dark-red'Hongdeng' cherry by promoting the expression levels of anthocyanin synthesis related structural genes and transcription factors.