Abstract
The cyanidin (Cy), pelargonidin (Pg), and delphinidin (Dp) pathways are the three major branching anthocyanin biosynthesis pathways that regulate flavonoid metabolic flux and are responsible for red, orange, and blue flower colors, respectively. Different species have evolved to develop multiple regulation mechanisms that form the branched pathways. In the current study, five Senecio cruentus cultivars with different colors were investigated. We found that the white and yellow cultivars do not accumulate anthocyanin and that the blue, pink, and carmine cultivars mainly accumulate Dp, Pg, and Cy in differing densities. Subsequent transcriptome analysis determined that there were 43 unigenes encoding anthocyanin biosynthesis genes in the blue cultivar. We also combined chemical and transcriptomic analyses to investigate the major metabolic pathways that are related to the observed differences in flower pigmentation in the series of S. cruentus. The results showed that mutations of the ScbHLH17 and ScCHI1/2 coding regions abolish anthocyanin formation in the white and the yellow cultivars; the competition of the ScF3′H1, ScF3′5′H, and ScDFR1/2 genes for naringenin determines the differences in branching metabolic flux of the Cy, Dp, and Pg pathways. Our findings provide new insights into the regulation of anthocyanin branching and also supplement gene resources (including ScF3′5 ′H, ScF3′H, and ScDFRs) for flower color modification of ornamentals.
Highlights
Flower color produces some of the most beautiful displays in nature and serves an important function in the ecology and evolution of plants by attracting animal pollinators (Glover, 2007)
Through a combination of chemical and transcriptomic analyses, the major metabolic pathways related to different cultivars of S. cruentus flower pigmentation were investigated, the candidate genes that determined the biosynthesis and branch were isolated, and the regulatory mechanism of key genes was discussed
We have demonstrated the coloration mechanism underlying the different colors of S. cruentus (Figure 7)
Summary
Flower color produces some of the most beautiful displays in nature and serves an important function in the ecology and evolution of plants by attracting animal pollinators (Glover, 2007). Pg derivatives provide the basis for orange-red hues (one hydroxyl group), Cy derivatives for deep red hues (two hydroxyl groups) and Dp derivatives for blue hues (three hydroxyl groups; Boase et al, 2010). These three types of anthocyanidin production are quite variable, as stated by Wessinger and Rausher (2012). (lily), occupy more than 50% of the cutflower market (Tanaka et al, 2008) These flowers can only naturally accumulate Cy and lack the blue flower color series. An understanding of the regulation of anthocyanin branching and an investigation of the key genes underlying this process will be important for the reconstruction of new anthocyanin branches and for the modification of flower colors in these ornamental plants
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