The Flavonoid Pathway Regulates the Petal Colors of Cotton Flower

Although biochemists and geneticists have studied the cotton flower for more than one century, little is known about the molecular mechanisms underlying the dramatic color change that occurs during its short developmental life following blooming. Through the analysis of world cotton germplasms, we found that all of the flowers underwent color changes post-anthesis, but there is a diverse array of petal colors among cotton species, with cream, yellow and red colors dominating the color scheme. Genetic and biochemical analyses indicated that both the original cream and red colors and the color changes post-anthesis were related to flavonoid content. The anthocyanin content and the expression of biosynthesis genes were both increased from blooming to one day post-anthesis (DPA) when the flower was withering and undergoing abscission. Our results indicated that the color changes and flavonoid biosynthesis of cotton flowers were precisely controlled and genetically regulated. In addition, flavonol synthase (FLS) genes involved in flavonol biosynthesis showed specific expression at 11 am when the flowers were fully opened. The anthocyanidin reductase (ANR) genes, which are responsible for proanthocyanidins biosynthesis, showed the highest expression at 6 pm on 0 DPA, when the flowers were withered. Light showed primary, moderate and little effects on flavonol, anthocyanin and proanthocyanidin biosynthesis, respectively. Flavonol biosynthesis was in response to light exposure, while anthocyanin biosynthesis was involved in flower color changes. Further expression analysis of flavonoid genes in flowers of wild type and a flavanone 3-hydroxylase (F3H) silenced line showed that the development of cotton flower color was controlled by a complex interaction between genes and light. These results present novel information regarding flavonoids metabolism and flower development.     

Isolation of amaranthin synthetase from Chenopodium quinoa and construction of an amaranthin production system using suspension‐cultured tobacco BY‐2 cells

Betalains are plant pigments primarily produced by plants of the order Caryophyllales. Because betalain possesses anti‐inflammatory and anticancer activities, it may be useful as a pharmaceutical agent and dietary supplement. Recent studies have identified the genes involved in the betalain biosynthesis of betanin. Amaranthin and celosianin II are abundant in the quinoa (Chenopodium quinoa Willd.) hypocotyl, and amaranthin comprises glucuronic acid bound to betanin; therefore, this suggests the existence of a glucuronyltransferase involved in the synthesis of amaranthin in the quinoa hypocotyl. To identify the gene involved in amaranthin biosynthesis, we performed a BLAST analysis and phylogenetic tree analysis based on sequences homologous to flavonoid glycosyltransferase, followed by expression analysis on the quinoa hypocotyl to obtain three candidate proteins. Production of amaranthin in a transient Nicotiana benthamiana expression system was evaluated for these candidates and one was identified as having the ability to produce amaranthin. The gene encoding this protein was quinoa amaranthin synthetase 1 (CqAmaSy1). We also created a transgenic tobacco bright yellow‐2 (BY‐2) cell line wherein four betalain biosynthesis genes were introduced to facilitate amaranthin production. This transgenic cell line produced 13.67 ± 4.13 μm (mean ± SEM) amaranthin and 26.60 ± 1.53 μm betanin, whereas the production of isoamaranthin and isobetanin could not be detected. Tests confirmed the ability of amaranthin and betanin to slightly suppress cancer cell viability. Furthermore, amaranthin was shown to significantly inhibit HIV‐1 protease activity, whereas betanin did not.     

Gene Silencing of BnTT10 Family Genes Causes Retarded Pigmentation and Lignin Reduction in the Seed Coat of Brassica napus

Yellow-seed (i.e., yellow seed coat) is one of the most important agronomic traits of Brassica plants, which is correlated with seed oil and meal qualities. Previous studies on the Brassicaceae, including Arabidopsis and Brassica species, proposed that the seed-color trait is correlative to flavonoid and lignin biosynthesis, at the molecular level. In Arabidopsis thaliana, the oxidative polymerization of flavonoid and biosynthesis of lignin has been demonstrated to be catalyzed by laccase 15, a functional enzyme encoded by the AtTT10 gene. In this study, eight Brassica TT10 genes (three from B. napus, three from B. rapa and two from B. oleracea) were isolated and their roles in flavonoid oxidation/polymerization and lignin biosynthesis were investigated. Based on our phylogenetic analysis, these genes could be divided into two groups with obvious structural and functional differentiation. Expression studies showed that Brassica TT10 genes are active in developing seeds, but with differential expression patterns in yellow- and black-seeded near-isogenic lines. For functional analyses, three black-seeded B. napus cultivars were chosen for transgenic studies. Transgenic B. napus plants expressing antisense TT10 constructs exhibited retarded pigmentation in the seed coat. Chemical composition analysis revealed increased levels of soluble proanthocyanidins, and decreased extractable lignin in the seed coats of these transgenic plants compared with that of the controls. These findings indicate a role for the Brassica TT10 genes in proanthocyanidin polymerization and lignin biosynthesis, as well as seed coat pigmentation in B. napus.     

24-Epibrassinolide enhances 5-ALA-induced anthocyanin and flavonol accumulation in calli of ‘Fuji’ apple flesh

Color is a key factor for fruit commercial value. 5-Aminolevulinic acid (5-ALA), as an eco-friendly plant growth regulator, shows an attractively promotive effect on plant secondary metabolism, especially for fruit coloration. Brassinosteroids (BRs) can also improve plant flavonoid biosynthesis. No information is now available on the relationship between 5-ALA and BR. Here, we found that 1.5 mg L^?1 24-epibrassinolide (24-EBL) promoted 50 mg L^?1 5-ALA-induced anthocyanin accumulation, while, brassinazole (Brz) significantly inhibited the 5-ALA-induced flavonoid accumulation. HPLC analysis further showed that the inductive effects of 5-ALA on the accumulation of cyanidin-3-galactoside, quercetin-3-galactoside, quercetin and kaempferol were elevated by 24-EBL, but impaired by Brz. These results suggest that brassinolide biosynthesis might involve in 5-ALA-induced flavonoid accumulation. Gene expression analysis showed that 5-ALA and 5-ALA?+?24-EBL induced the expression of regulatory genes MdMYB10, MdMYB9, MdbHLH3 and MdbHLH33. These two treatments also up-regulated the structural gene expressions of anthocyanin biosynthesis and transportation, including MdCHS, MdF3′H, MdDFR, MdANS, MdUFGT, MdGST and MdMATE, as well as flavonol biosynthetic gene MdFLS. But Brz decreased 5-ALA-induced up-regulation of these genes. In addition, 5-ALA also induced the expression of MdBRI1, MdBAK1 and MdBZR1, which are involved in brassinolide signal transduction. These results indicate that 24-EBL enhances 5-ALA-promoted expression of genes related to flavonoid biosynthesis and brassinolide signal transduction, while Brz exhibits the opposite effects. Taken together, we propose that 24-EBL is involved in 5-ALA-induced anthocyanin and flavonol accumulation in calli of apples. Our results provide new insights into 5-ALA-induced fruit coloration.