Key Enzyme Genes Of Flavonoid Biosynthesis In Banana Fruit

Banana is the world largest fresh fruit in trade value.Flavonoids content in banana fruit is an important physiological index to measure fruit quality.The recent studies about flavonoids in banana fruit mainly focused on the changed pattern of content in physiological level,while the expression and regulation of the key enzymes in molecular level remains unknown.In the present study,’baxijiao’ was used as the material.The dynamic characteristics of total flavonoids content in different fruit developing and ripening stages was investigated.The differentially expressed patterns in different organs and different fruit developing and ripening stages of six key enzyme gene families in flavonoids biosynthesis metabolism were analyzed by RNA-seq.Two co-expression regulatory networks were constructed by using CHS and FLS as the cores and the upstream key regulatory factors were predicted based on the RNA-seq data.The interactions of the predicted transcription factors and target genes were identified by yeast one hybrid.The main results were obtained as follows:1.The flavonoids contents gradually decreased from flower emerging to flower cutting to fruit harvesting and reached the lowest at harvesting.During postharvest banana fruit ripening process,the flavonoids contents displayed a slight increase and then decreased.2.A total of 78 genes belong to six key enzyme gene families in flavonoids biosynthesis were differentially expressed in different organs and different fruit developing and postharvest ripening stages.Among them,11 genes were highly expressed in fruits,of which 8 were specifically expressed in fruits..3.Ten key enzyme genes were randomly selected to identity their expressions by qRT-PCR,the results were in line with RNA-seq.4.Transcriptome and qRT-PCR results showed that MaCHS gene and MaFLS gene were highly expressed in fruits,and it was speculated that they played an important role in the biosynthesis of banana flavonoids.5.Analysis of the transcriptome data co-expression regulatory network revealed that 10 transcription factors may bind to the promoter of the MaCHS gene;20 transcription factors may bind to the promoter of the MaFLS gene.6.The promoters of MaCHS and MaFLS were isolated and the cis acting elements were analyzed.The analysis was performed using PlantCARE.The software analysis showed that both promoters contained core promoter sequence structures such as TATA-box,GC-box,and CAAT-box,and the MaCHS promoter had drought,ABA,and salicylic acid activation induction.MYB binding site and other cis-acting elements,MaFLS promoter hypoxia,GA,drought,auxin-inducing elements,wound response elements and MYB binding sites and other cis-acting elements.7.The result indicated that some typical transcription factor binding domains were found.The result of yeast one hybrid demonstrated that the transcription factors of MabHLH,MaERF,MaMIKC,MaMYB and MaWRKY could really interact with MaCHS promoter.MaM-type,MaOFP and MaWRKY could interact with MaFLS promoter.These results indicated that these transcription factors could regulate the fruit flavonoids biosynthesis by regulating the expressions of key enzyme genes.