Flavonoids Accumulation in Fruit Peel and Expression Profiling of Related Genes in Purple (Passiflora edulis f. edulis) and Yellow (Passiflora edulis f. flavicarpa) Passion Fruits

Flavonoids play a key role as a secondary antioxidant defense system against different biotic and abiotic stresses, and also act as coloring compounds in various fruiting plants. In this study, fruit samples of purple (Passiflora edulis f. edulis) and yellow (Passiflora edulis f. flavicarpa) passion fruit were collected at five developmental stages (i.e., fruitlet, green, veraison, maturation, and ripening stage) from an orchard located at Nanping, Fujian, China. The contents of flavonoid, anthocyanin, proanthocyanin, and their metabolites were determined using ultra-performance liquid chromatography-mass spectrometry (UPLC-MS), activities of key enzymes involved in flavonoid metabolism were measured, and expression profiling of related genes was done using quantitative real-time PCR (qRT-PCR). The results revealed that total flavonoids, anthocyanins, and procyanidins were found to be increased in the fruit peel of both cultivars with fruit maturity. Total flavonoids, anthocyanins, procyanidins, flavonoid metabolites (i.e., rutin, luteolin, and quercetin), and anthocyanin metabolites (i.e., cyanidin-3-O-glucoside chloride, peonidin-3-O-glucoside, and pelargonidin-3-O-glucoside) were found abundant in the peel of purple passion fruit, as compared to yellow passion fruit. Principle component analysis showed that the enzymes, i.e., C4H, 4CL, UFGT, and GST were maybe involved in the regulation of flavonoids metabolism in the peel of passion fruit cultivars. Meanwhile, PePAL4, Pe4CL2,3, PeCHS2, and PeGST7 may play an important role in flavonoid metabolism in fruit peel of the passion fruit. This study provides new insights for future elucidation of key mechanisms regulating flavonoids biosynthesis in passion fruit.

Genome-wide identification of WD40 superfamily genes and prediction of WD40 gene of flavonoid-related genes in Ginkgo biloba

The WD40 transcription factor family is a superfamily found in eukaryotes and implicated in regulating growth and development. In this study, 167 WD40 family genes are identified in the Ginkgo biloba genome. They are divided into 5 clusters and 16 subfamilies based on the difference analysis of a phylogenetic tree and domain structures. The distribution of WD40 genes in chromosomes, gene structures, and motifs is analyzed. Promoter analysis shows that five GbWD40 gene promoters contain the MYB binding site participating in the regulation of flavonoid metabolism, suggesting that these five genes may participate in the regulation of flavonoid synthesis in G. biloba. The correlation analysis is carried out based on FPKM value of WD40 gene and flavonoid content in 8 tissues of G. biloba. Six GbWD40 genes that may participate in flavonoid metabolism are screened. The biological functions of the WD40 family genes in G. biloba are systematically analyzed, providing a foundation for further elucidating their regulatory mechanisms. A number of WD40 candidate genes involved in the biosynthesis and metabolism of G. biloba also predicted. This study presents an important basis and direction for conducting further research on the regulatory network of flavonoid synthesis and metabolism.

Transcriptome analysis reveals regulatory networks and hub genes in flavonoid metabolism of Rosa roxburghii

Rosa roxburghii Tratt, the most popular fruit that blooms in the southwest of China, is rich in flavonoids. However, the regulatory network and critical genes involved in the metabolism of flavonoid compounds in R. roxburghii are still unknown. In this study, we revealed that flavonoid, anthocyanin and catechin accumulated at different levels in various tissues of R. roxburghii . We further obtained and analyzed differentially expressed genes (DEGs) involved in flavonoid metabolism from five samples of R. roxburghii by transcriptome sequencing. A total of 1 130 DEGs were identified, including 166 flavonoid pathway biosynthesis genes, 622 transcription factors, 301 transporters, and 221 cytochrome P450 proteins. A weighted gene co-expression network analysis (WGCNA) of the DEGs uncovered different co-expression networks. In terms of biosynthesis enzymes, cytochrome P450 CYP749A22 and CYP72A219 were highlighted in regulation flavonoids content. Anthocyanin 3-O-glucosyltransferase and F3’H were the top two critical enzymes for anthocyanin content. In contrast, caffeic acid 3-O-methyltransferase, 4-coumarate-CoA ligase, and shikimate O-hydroxycinnamoyl transferase were essential for catechin accumulation. Additionally, the eigengene network of the “black” module had high correlations with total flavonoid (r= 0.9, p=5e-06). There were 26 eigengenes in the “black” module, including six flavonoid biosynthesis, 14 TFs and six transporters. Among them, besides cytochrome P450 proteins ( DN136557_c0_g1 , DN135573_c0_g1 and DN145971_c4_g1 ), isoflavone-hydroxylase ( DN143321_c3_g1 ) was crucial for total flavonoids content based on the high degree of connectivity. The transcription factors RrWRKY45 ( DN142829_c1_g5 ), RrTCP20 ( DN146443_c1_g1) and RrERF118 ( DN141507_c3_g2) were significantly correlated with flavonoids in R. roxburghii . The present transcriptomic and biochemical data on metabolites should encourage further investigation on functional genomics and breeding of R. roxburghii with strong pharmaceutical potential.

GABA and Its Shunt’s Contributions to Flavonoid Biosynthesis and Metabolism in the Tea Plat (Camellia Sinensis)

Background: γ-Aminobutyric acid (GABA), a signal molecule, is regarded as the intersection of carbon and nitrogen metabolism, but its contributions to flavonoid metabolism in tea plants during the whole growth cycle remain unclear, and the correlation between the GABA shunt and flavonoid metabolism in tea plants is worth exploring. Secondary metabolites and their correlations with the taste qualities of tea plants (Camellia sinensis) during different seasons have been investigated.Results: Related secondary metabolites and transcript profiles of genes encoding enzymes in the GABA shunt, flavonoid pathway and polyamine biosynthesis were measured throughout the whole tea plant growth season and after exogenous GABA applications. In addition, levels of differentially expressed proteins were measured after treatment with or without exogenous GABA. The tea leaves showed the highest metabolite concentrations in spring. CsGAD, CsGABAT, CsSPMS, CsODC, CsF3H and CsCHS were found to be important genes in the GABA and anthocyanin network. Conclusion: GABA and anthocyanin concentrations showed a positive correlation, to some extent, and CsF3H and CsCHS played important roles in the GABA and anthocyanin network. Further studies should focus on exploring GABA and flavonoid metabolism through the transgenic engineering of tea plants.