Analysis Of Petal Pigment And Related Gene Expression During The Flower Color Change Of Paeonia Otii 'feng Dan'

Tree peony(Paeonia suffruticosa Andr.),as one of the ten most famous traditional flowers in China,is colorful and graceful,and it has always been loved by the people.Although there are nine color systems for peony flowers,there are few flower color change varieties.The flower color of Paeonia ostii ‘feng dan' changes during the flowering.The flower color gradually changes from purple to white,which has high ornamental value.However,the molecular mechanism underlying flower color change is still unclear.In this study,the petals of ‘feng dan' tree peony in five different flowering stages were used as experimental materials to explore the relationship between the composition and content of petal pigments and the related genes of anthocyanin biosynthesis during the flower color change.This research would be helpful to elucidate the mechanism of flower color change in tree peony and to cultivate the tree peony flower color change varieties through genetic engineering.The main research results are as follows:A chroma meter was used to measure the color related value of L*,a*,b*,C* of five different stages fresh petals,and the flower color of each stages were digitally described in detail.In the process of the ‘feng dan' tree peony flower gradually changing from purple to white,the lightness L* value of the flower color increased significantly,the hue a* value decreasesd greatly,and the chroma C* value decreased.The qualitative and quantitative analysis of the pigment composition of ‘feng dan' tree peony petals was performed high-performance liquid chromatograph.Two kinds of anthocyanins peonidin-3,5-di-O-glucoside(Pn3G5G)and cyanidin-3,5-di-O-glucoside(Cy3G5G)were detected.Pn3G5 G is the main anthocyanin,and the content of Pn3G5 G in each stage accounts for more than 95% of the total anthocyanin content in the corresponding stage.During the flowering,the total anthocyanin content gradually decreased from unfold petal stage(S1)to flower withering stage(S5),and stage S5 decreased by 84.11% compared with stage S1.The ‘feng dan' tree peony flower contains eight kinds of mono-phenols: catechin,naringenin,p-coumaric acid,apigenin,aureoflavin,luteolin,quercetin and kaempferol,and most of mono-phenols content have different degrees of reduction.Monophenols as a co-pigment plays an auxiliary role in flower color formation.The flower color of ‘feng dan' tree peony changed from purple to white mainly due to the significant reduction of the total anthocyanin content.The expression of related structural genes and regulatory genes in the anthocyanin synthesis pathway were measured using quantitative real-time PCR.DFR,ANS and MYB114 L showed higher expression levels in the S1 stage,and the relative expression levels in the S1 stage were 259 times,68 times and 74 times of the S5 stage,respectively.The relative expression levels of PAL,DFR,ANS,MYB22,MYB114 L,and b HLH1 genes in the five stages showed a gradual downward trend,which was consistent with the change trend of total anthocyanin content,and showed a very significant positive correlation.The expression pattern of MYB113 is opposite to the expression pattern of DFR,ANS and the total anthocyanin content,and there is a very significant negative correlation.PAL,DFR and ANS are considered to be the key structural genes in the anthocyanins biosynthesis of ‘feng dan' tree peony.The transcription factors MYB22,MYB114 L,MYB113 and b HLH1 may play an important role in regulating the expression of structural genes DFR and ANS.The transcription factor MYB113 may negatively regulate the anthocyanins biosynthesis of ‘feng dan' tree peony,and the specific regulatory mechanism needs further study.