The Flavonoid Biosynthesis Network in Plants

Abstract

Flavonoids are an important class of secondary metabolites widely found in plants, contributing to plant growth and development and having prominent applications in food and medicine. The biosynthesis of flavonoids has long been the focus of intense research in plant biology. Flavonoids are derived from the phenylpropanoid metabolic pathway, and have a basic structure that comprises a C15 benzene ring structure of C6-C3-C6. Over recent decades, a considerable number of studies have been directed at elucidating the mechanisms involved in flavonoid biosynthesis in plants. In this review, we systematically summarize the flavonoid biosynthetic pathway. We further assemble an exhaustive map of flavonoid biosynthesis in plants comprising eight branches (stilbene, aurone, flavone, isoflavone, flavonol, phlobaphene, proanthocyanidin, and anthocyanin biosynthesis) and four important intermediate metabolites (chalcone, flavanone, dihydroflavonol, and leucoanthocyanidin). This review affords a comprehensive overview of the current knowledge regarding flavonoid biosynthesis, and provides the theoretical basis for further elucidating the pathways involved in the biosynthesis of flavonoids, which will aid in better understanding their functions and potential uses.

A Comprehensive View on the Quercetin Impact on Colorectal Cancer

“…The synthesis of quercetin is heavily linked to the general flavonoid biosynthetic pathway in plants. Therefore, it is dependent on the transcription regulation of all pathways leading up to anthocyanins, as they represent products that in their biosynthesis require the most steps of the flavonoid metabolism [ 42 ]. Transcription factors such as the basic helix–loop–helix (bHLH), R2R3-MYB, and the WD40 proteins lead to the activation, and differential temporal and spatial expression of the structural genes necessary in the biosynthesis [ 22 , 42 , 43 ].…”

“…Therefore, it is dependent on the transcription regulation of all pathways leading up to anthocyanins, as they represent products that in their biosynthesis require the most steps of the flavonoid metabolism [ 42 ]. Transcription factors such as the basic helix–loop–helix (bHLH), R2R3-MYB, and the WD40 proteins lead to the activation, and differential temporal and spatial expression of the structural genes necessary in the biosynthesis [ 22 , 42 , 43 ]. Furthermore, concomitant increase in the synthesis of quercetin also occurs alongside the synthesis of lignin, mainly due to expression upregulation of the same set of enzymes pertaining to the phenylpropane metabolic pathway, pathway responsible for the synthesis of both molecules [ 44 ].…”

“…Furthermore, concomitant increase in the synthesis of quercetin also occurs alongside the synthesis of lignin, mainly due to expression upregulation of the same set of enzymes pertaining to the phenylpropane metabolic pathway, pathway responsible for the synthesis of both molecules [ 44 ]. Moreover, several studies identify influences of environmental stressors, such as light and soil composition, as regulators of flavonoid synthesis [ 22 , 42 ]. The UV-B radiation and, consequently, the photosynthetic photon flux impact the biosynthesis of quercetin, with stronger photon fluxes being positively correlated with higher amounts of synthesized quercetin [ 45 , 46 ].…”

Genome-Wide Identification and Expression Profiles of 13 Key Structural Gene Families Involved in the Biosynthesis of Rice Flavonoid Scaffolds

“…Nearly all flavonoids contain the common diphenylpropane (C6-C3-C6) carbon framework with two aromatic rings (A-ring and B-ring) interconnected by a three-carbon heterocyclic pyran ring (C-ring chain) [ 2 , 3 ]. Based on the degree of heterocyclic C-ring oxidation, the position of hydroxyl and methyl groups on the A- and B-rings and the degree of modifications (including glycosylation, acylation and polymerization ), flavonoids can be chiefly categorized into six classes: flavones, flavanones, flavonols, flavanols, anthocyanins and isoflavones [ 3 , 4 ]. An enormous amount of research during the last few decades has revealed that flavonoids, as the most bioactive plant secondary metabolites, might exhibit a wide range of physiological functions in plant growth, development, reproduction and stress defense [ 5 , 6 , 7 ].…”

“…To date, over 9000 flavonoid molecules have been identified from various plant species [ 4 ], and the molecular mechanisms of enzymes catalyzing flavonoid biosynthesis have also been well established, such as in Arabidopsis thaliana , Solanum lycopersicum (tomato), Glycine max , Phaseolus vulgaris and Vitis vinifera [ 2 , 38 , 39 ]. O. sativa (rice), as an experimental system for monocots, is the most economically important food staple crop for human nutrition [ 35 ].…”