On the biogenesis of flavone O-glycosides and C-glycosides in the lemnaceae

Wallace, James W.; Mabry, Tom J.; Alston, Ralph E.

doi:10.1016/s0031-9422(00)85800-8

Cited by 51 publications

(19 citation statements)

References 2 publications

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“…On the other hand, CYP93G2 is a flavanone 2-hydroxlase, which produces 2-hydroxyflavanones for immediate C-glycosylation, followed by the formation of the flavone nucleus (Du et al, 2010). Our previous work essentially confirmed the early speculation that separate biosynthetic routes (Wallace et al, 1969;Wallace and Grisebach, 1973) are responsible for these two predominant types of flavone-derived metabolites present in a variety of monocot species.…”

supporting

confidence: 79%

Completion of Tricin Biosynthesis Pathway in Rice: Cytochrome P450 75B4 Is a Unique Chrysoeriol 5′-Hydroxylase

2015

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Flavones are ubiquitously accumulated in land plants, but their biosynthesis in monocots remained largely elusive until recent years. Recently, we demonstrated that the rice (Oryza sativa) cytochrome P450 enzymes CYP93G1 and CYP93G2 channel flavanones en route to flavone O-linked conjugates and C-glycosides, respectively. In tricin, the 39,59-dimethoxyflavone nucleus is formed before O-linked conjugations. Previously, flavonoid 39,59-hydroxylases belonging to the CYP75A subfamily were believed to generate tricetin from apigenin for 39,59-O-methylation to form tricin. However, we report here that CYP75B4 a unique flavonoid B-ring hydroxylase indispensable for tricin formation in rice. A CYP75B4 knockout mutant is tricin deficient, with unusual accumulation of chrysoeriol (a 39-methoxylated flavone). CYP75B4 functions as a bona fide flavonoid 39-hydroxylase by restoring the accumulation of 39-hydroxylated flavonoids in Arabidopsis (Arabidopsis thaliana) transparent testa7 mutants and catalyzing in vitro 39-hydroxylation of different flavonoids. In addition, overexpression of both CYP75B4 and CYP93G1 (a flavone synthase II) in Arabidopsis resulted in tricin accumulation. Specific 59-hydroxylation of chrysoeriol to selgin by CYP75B4 was further demonstrated in vitro. The reaction steps leading to tricin biosynthesis are then reconstructed as naringenin → apigenin → luteolin → chrysoeriol → selgin → tricin. Hence, chrysoeriol, instead of tricetin, is an intermediate in tricin biosynthesis. CYP75B4 homologous sequences are highly conserved in Poaceae, and they are phylogenetically distinct from the canonical CYP75B flavonoid 39-hydroxylase sequences. Recruitment of chrysoeriol-specific 59-hydroxylase activity by an ancestral CYP75B sequence may represent a key event leading to the prevalence of tricin-derived metabolites in grasses and other monocots today.

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confidence: 79%

Completion of Tricin Biosynthesis Pathway in Rice: Cytochrome P450 75B4 Is a Unique Chrysoeriol 5′-Hydroxylase

2015

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“…In fact, early radiotracer experiments in Lemnaceae plants demonstrated that 14 C-labeled flavones were incorporated into O-glycosylated and O-methylated flavones but not flavone C-glycosides (Wallace et al, 1969). The formation of tricin (39,59-O-dimethoxylated) requires the activities of flavonoid 39,59-hydroxylase (F3959H) to generate hydroxyl groups in the B ring for the O-methylation reactions (Fig.…”

Section: Cyp93b11) Involved In Root Nodulationmentioning

confidence: 99%

Cytochrome P450 93G1 Is a Flavone Synthase II That Channels Flavanones to the Biosynthesis of Tricin O-Linked Conjugates in Rice

et al. 2014

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Flavones are a major class of flavonoids with a wide range of physiological functions in plants. They are constitutively accumulated as C-glycosides and O-linked conjugates in vegetative tissues of grasses. It has long been presumed that the two structural modifications of flavones occur through independent metabolic routes. Previously, we reported that cytochrome P450 93G2 (CYP93G2) functions as a flavanone 2-hydroxylase (F2H) that provides 2-hydroxyflavanones for C-glycosylation in rice (Oryza sativa). Flavone C-glycosides are subsequently formed by dehydratase activity on 2-hydroxyflavanone C-glycosides. On the other hand, O-linked modifications were proposed to proceed after the flavone nucleus is generated. In this study, we demonstrate that CYP93G1, the closest homolog of CYP93G2 in rice, is a bona fide flavone synthase II (FNSII) that catalyzes the direct conversion of flavanones to flavones. In recombinant enzyme assays, CYP93G1 desaturated naringenin and eriodictyol to apigenin and luteolin, respectively. Consistently, transgenic expression of CYP93G1 in Arabidopsis (Arabidopsis thaliana) resulted in the accumulation of different flavone O-glycosides, which are not naturally present in cruciferous plants. Metabolite analysis of a rice CYP93G1 insertion mutant further demonstrated the preferential depletion of tricin O-linked flavanolignans and glycosides. By contrast, redirection of metabolic flow to the biosynthesis of flavone C-glycosides was observed. Our findings established that CYP93G1 is a key branch point enzyme channeling flavanones to the biosynthesis of tricin O-linked conjugates in rice. Functional diversification of F2H and FNSII in the cytochrome P450 CYP93G subfamily may represent a lineage-specific event leading to the prevalent cooccurrence of flavone C-and O-linked derivatives in grasses today.

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“…Boiling water has been found suitable for the extraction of polyglycosides such as acacetin 7-0-diglucuronide (Okigawa et al, 1971a) and the flavonepolysaccharide compound from Monoclea forsteri (Markharn, 1972), and also for the isolation of compounds such as flavandiols, catechins and procyanidins. Traces of acid are occasionally incorporated in the solvent for the extraction of flavonoid glycosides (Wallace et al , 1969) aIthough this practice is normally reserved for the extraction of anthocyanins and anthocyanidins (Seshadri, 1962;Harborne, 1967b). The use of acid, however, can lead to hydro lysis of glycosidic materials.…”

Section: Plant Preparation and Extractionmentioning

confidence: 99%

Isolation Techniques for Flavonoids

Markham¹

1975

The Flavonoids

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On the biogenesis of flavone O-glycosides and C-glycosides in the lemnaceae

Cited by 51 publications

References 2 publications

Completion of Tricin Biosynthesis Pathway in Rice: Cytochrome P450 75B4 Is a Unique Chrysoeriol 5′-Hydroxylase

Completion of Tricin Biosynthesis Pathway in Rice: Cytochrome P450 75B4 Is a Unique Chrysoeriol 5′-Hydroxylase

Cytochrome P450 93G1 Is a Flavone Synthase II That Channels Flavanones to the Biosynthesis of Tricin O-Linked Conjugates in Rice

Isolation Techniques for Flavonoids

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