Study On The Mechanism Of Anthocyanin Synthesis In The Fruit Skin Of Ophiopogon Japonicas And Liriope Spicata

Ophiopogon japonicus and Liriope spicata are ornamental ground cover plants in liliaceae.But they are confused in cultivation,while the color of the fruit is an important distinguishing feature.The fruit skin of O.japonicus turns from green to blue when ripe,while the fruit skin of L.spicata turns from green to black when ripe.To find the difference in anthocyanin synthesis between the two species,five developmental stages of O.japonicus fruit and three developmental stages of L.spicata were studied by metabolome and transcriptome analysis.After separating the key anthocyanins and key genes,the differences between the two species were compared and the mechanism of biosynthesis of anthocyanin was discussed.The main results were as followed:(1)Metabolomic analysis showed that five major anthocyanins in five developmental stages(S1-S5)of O.japonicus had significant effects on the coloration of fruits.They were Delphinidin3-O-rutinoside,Delphinidin 3-O-glucoside,Petunidin 3-O-rutinoside,Cyanidin 3-O-galactoside and Delphinidin 3-O-galactoside.Especially for Delphinidin 3-O-rutinoside,the content of which accumulated rapidly to 67.6% in S4.When modeling the weighted gene co-expression network analysis(WGCNA)and co-expression network between genes and anthocyanins,six gene modules were found to be highly correlated with anthocyanin content change(P<0.05)Among the six gene modules,F3’5’H,ANS and UFGT genes were identified as the hub gene.Moreover,MYB gene was co-expressed with hub genes and key anthocyanins.(2)Metabolomic analysis showed that eight key anthocyanins in three developmental stages(L1-L3)of L.spicata had significant effects on fruit color transformation.They were Delphinidin3-O-glucoside,Peonidin 3-O-rutinoside,Delphinidin 3-O-rutinoside,Petunidin 3-O-rutinoside,Malvidin 3-O-galactoside,Petunidin 3-O-glucoside,Cyanidin 3-O-rutinoside,Cyanidin3-O-glucoside.Among them,Peonidin 3-O-rutinoside and Delphinidin 3-O-glucoside were the key anthocyanins to distinguish the green and black fruits of L.spicata,with the highest VIP values corresponding to the stages L1-L2 and L2-L3,respectively.WGCNA and co-expression network between genes and anthocyanins revealed that four gene modules were highly correlated with anthocyanin content change(P<0.05).In the four modules,structural genes including 4CL,F3 H,F3’H,F3’5’H,UFGT and transcription factor genes including MYB and b HLH were the hub genes and were highly interconnected.(3)Comparing the maturation period(S4-L2)in two species of fruits,it was found that the proportion of anthocyanins was the key to coloration.Blue anthocyanin types accounted for a high proportion of metabolites in S4,which was far more than red anthocyanin types.On the contrary,the content of red anthocyanins types of L.spicata fruit in L2 was much higher than that of O.japonicus fruit in S4,especially Peonidin.The proportion of red anthocyanin types was similar to that of blue anthocyanin types in L2.Multivariate statistics analysis showed that Peonidin 3-O-rutinoside had the greatest influence on the color difference,and the VIP value was the highest.(4)Comparing the key genes of O.japonicus and L.spicata,it was found that early flavonoid synthesis genes including 4CL and F3 H were highly expressed in L.spicata.The differentially expressed b HLH gene was only screened in L.spicata,which belongs to IIIf subgroup.Lsb HLH had amino acid residues K161,A163 and motif H-E-R,which related to anthocyanin synthesis.None of the above genes could directly determine the proportion of anthocyanin types.While F3’H and F3’5’H were the key genes that caused the difference in the proportion of anthocyanins between two species of fruits.The competition between F3’H and F3’5’H for substrate kaempferol was the key to the flow of anthocyanins from two species of fruits.In the high expression level of Oj F3’5’Hs,the intermediate was more easily be modified by 3’,5’-hydroxylation.On the other hand,Ls F3’H4 protein was able to build up a large number of 3’-hydroxy intermediates,while Ls F3’5’H2 was estimated to catalyze 3’,5’-hydroxylation reaction and accumulated dihydromyricetin.Based on the data of transcriptome and metabolome,the key anthocyanins and the key genes for color transformation in two species of fruits were screened for the first time.On the other hand,the material basis and molecular regulation differences of color difference in two species of fruits between O.japonicus and L.spicata were revealed.These works lay a foundation for the subsequent validation of the active sites of key enzyme gene and have important theoretical and practical significance.