Abstract
Anthocyanins are distributed ubiquitously to terrestrial plants and chalcone isomerase (CHI) catalyzes the stereospecific isomerization of chalcones – a committed step in the anthocyanin biosynthesis pathway. In this study, one gene encoding CHI was isolated from Ophiorrhiza japonica and designated as OjCHI. Multiple sequence alignments and phylogenetic analysis revealed that OjCHI had the conserved CHI active site residues and was classified into type I CHI group. In order to better understand the mechanisms of anthocyanin synthesis in O. japonica, integrative analysis between metabolites and OjCHI expression was conducted. The results showed OjCHI expression matched the accumulation patterns of anthocyanins not only in different tissues but also during the flower developmental stages, suggesting the potential roles of OjCHI in the biosynthesis of anthocyanin. Then biochemical analysis indicated that recombinant OjCHI protein exhibited a typical type I CHI activity which catalyzed the production of naringenin from naringenin chalcone. Moreover, expressing OjCHI in Arabidopsis tt5 mutant restored the anthocyanins and flavonols phenotype of hypocotyl, cotyledon and seed coat, indicating its function as a chalcone isomerase in vivo. In summary, our findings reveal the in vitro as well as in vivo functions of OjCHI and provide a resource to understand the mechanism of anthocyanin biosynthesis in O. japonica.
Highlights
Anthocyanins, a kind of natural pigment, are widespread in plants and predominantly found in flowers, fruits, vegetables, cereals as well as teas (Pervaiz et al, 2017)
chalcone isomerase (CHI) are known as the key enzymes which exhibit vital regulatory function during the anthocyanin biosynthesis (Grotewold, 2006; Zhou et al, 2014)
Given the importance of this enzyme, comprehensive study of CHI involved in flavonoid biosynthesis has become one of the hot spots in plant secondary metabolism research
Summary
Anthocyanins, a kind of natural pigment, are widespread in plants and predominantly found in flowers, fruits, vegetables, cereals as well as teas (Pervaiz et al, 2017). Among many pigments in nature, anthocyanins assume a critical role because they can confer abundant colors (orange, pink, red, blue, and purple) to different organs of plants such as root, stem, leaf, flower, fruit, and tubers (Grotewold, 2006). Researches with animals and clinical studies have demonstrated that anthocyanins have an effect in reducing the risk of coronary diseases, stroke and cancer (Thibado et al, 2018). They have the biological function for attracting pollinators. Anthocyanins are interesting secondary plant metabolites as they can be used as plant/food colorants, warning signals, antifeedants, healthpromoting agent and so on
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