Abstract
Flavonoids, which are a diverse class of phytonutrients, are used by organisms to respond to nearly all abiotic stresses and are beneficial for human health. Glycosyltransferase, used during the last step of flavonoid biosynthesis, is important in flavonoid enrichment. However, little is known about glycosyltransferase in the orchid Dendrobium catenatum (D. officinale). In this study, we isolated a novel C-glycosyltransferase (designated DcaCGT) from the orchid D. catenatum by identifying and analyzing 82 putative genes in the GT1 family. DcaCGT could specifically catalyze not only di-C-glycosylation but also O-glycosylation. Apart from the normal function of catalyzing 2-hydroxynaringenin and phloretin to the respective di-C-glycosides, DcaCGT also catalyzes apigenin to cosmosiin. Targeted metabolic profiling of the substrates (2-hydroxynaringenin, phloretin, and apigenin) and products (vitexin, isovitexin, vicenin-2, nothofagin, 3’,5’-di-C-glucosylphloretin, and cosmosiin) in different tissues showed that vicenin-2 was the most abundant product of this novel enzyme. Cosmosiin was detected in flowers and flower buds. We also established that DcaCGT functions expanded throughout the evolution of D. catenatum. Residual OGT activity may help D. catenatum resist drought stress. Our study illustrates the function, origin, and differentiation of DcaCGT and provides insights into glycosylation and molecular propagation processes, which can be used to improve the production of flavonoids by the cultivated medicinal plant D. catenatum.
Highlights
Flavonoids, a class of valuable secondary metabolites, are widely distributed in plants
Our study provides the biosynthetic pathways of di-C/O-glucosylflavones in D. catenatum, and performs a molecular phylogenetic analysis to offer insight into the evolution of the functional gene
These D. catenatum UGTs were phylogenetically divided into 16 groups, including 12 groups (A-G, I–M) that were identified in Arabidopsis[17, 3] groups (O-Q) that were identified in maize[18] and 1 group (R) that was found in seed plants[41]
Summary
Flavonoids, a class of valuable secondary metabolites, are widely distributed in plants. C-glycosylflavones are critical in plant physiology and are beneficial for human health. Vicenin[2] is an effective flavone that shows anti-inflammatory[6], antiglycating[7], antispasmodic[8], antiseptic[9], antiplatelet, antithrombotic[10], and anticancer[11,12] activity. Because flavonoids show such high biological activity, determining the pathways involved in the biosynthesis of flavonoid glycosides is important
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