Tricin—a potential multifunctional nutraceutical

Zhou, Jian‐Min; Ibrahim, Ragai K.

doi:10.1007/s11101-009-9161-5

Cited by 111 publications

(101 citation statements)

References 121 publications

(138 reference statements)

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“…Tricin is the first flavonoid that is recognized to be an authentic monomer involved in lignification (del Río et al, 2012;Lan et al, 2015). Moreover, tricin is already well recognized as a valuable healthpromoting compound due to its antioxidant, antiaging, anticancer, and cardioprotective potential (Zhou and Ibrahim, 2010;Li et al, 2016). Recent findings show that tricin incorporates into the lignin polymer of maize plants via 49-O-b cross-coupling with normal and acylated monolignols, acting as an initiation site for lignin polymerization because it can only start a lignin chain (Lan et al, 2015(Lan et al, , 2016a.…”

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Silencing CHALCONE SYNTHASE in Maize Impedes the Incorporation of Tricin into Lignin and Increases Lignin Content

et al. 2016

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Lignin is a phenolic heteropolymer that is deposited in secondary-thickened cell walls, where it provides mechanical strength. A recent structural characterization of cell walls from monocot species showed that the flavone tricin is part of the native lignin polymer, where it is hypothesized to initiate lignin chains. In this study, we investigated the consequences of altered tricin levels on lignin structure and cell wall recalcitrance by phenolic profiling, nuclear magnetic resonance, and saccharification assays of the naturally silenced maize (Zea mays) C2-Idf (inhibitor diffuse) mutant, defective in the CHALCONE SYNTHASE Colorless2 (C2) gene. We show that the C2-Idf mutant produces highly reduced levels of apigenin-and tricin-related flavonoids, resulting in a strongly reduced incorporation of tricin into the lignin polymer. Moreover, the lignin was enriched in b-b and b-5 units, lending support to the contention that tricin acts to initiate lignin chains and that, in the absence of tricin, more monolignol dimerization reactions occur. In addition, the C2-Idf mutation resulted in strikingly higher Klason lignin levels in the leaves. As a consequence, the leaves of C2-Idf mutants had significantly reduced saccharification efficiencies compared with those of control plants. These findings are instructive for lignin engineering strategies to improve biomass processing and biochemical production.

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Silencing CHALCONE SYNTHASE in Maize Impedes the Incorporation of Tricin into Lignin and Increases Lignin Content

et al. 2016

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“…Complete understanding of the biosynthetic route and its regulation will facilitate future attempts at targeted engineering of tricin-type flavanolignans as nutraceuticals in the edible tissue of rice (i.e. endosperm), which mainly consists of starch and protein but is deficient in phytochemicals (Zhou and Ibrahim, 2010). Using several combinations of rice and nonrice flavonoid structural genes under the control of tissue-specific promoters, different classes of flavonoids were recently successfully engineered in rice endosperm, embryo, and aleurone layer (Ogo et al, 2013).…”

Section: Cyp93b11) Involved In Root Nodulationmentioning

confidence: 99%

“…Currently, more than 9,000 flavonoid structures have been reported (Yun et al, 2008), and different classes are assigned based on the oxidation state in the middle C-ring (Schijlen et al, 2004). Among them, flavones are found extensively in land plants but are absent in almost all members of the Cruciferae (Martens and Mithöfer, 2005;Zhou and Ibrahim, 2010). In plants, flavones play important physiological roles, including UV protection (Schmitz-Hoerner and Weissenböck, 2003), interactions with other organisms (Peters et al, 1986;Kong et al, 2007), regulation of auxin transport (Mathesius et al, 1998), and copigmentation in flowers (Goto and Kondo, 1991).…”

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confidence: 99%

“…In fact, metabolite analysis revealed the accumulation of both C-and O-glycosides of flavones in vegetative tissues of rice (Shih et al, 2008). Glycosylation is a common structural modification in flavonoids, affecting their solubility, stability, and activities (Zhou and Ibrahim, 2010). Subsequently, a rice C-glucosyltransferase (OsCGT) was shown to catalyze UDP-Glc-dependent C-glucosylation of 2-hydroxyflavanone substrates (BrazierHicks et al, 2009).…”

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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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“…Tricin (a 39,59-dimethoxyflavone) is a flavonoid typically distributed in sedges, palms, and grasses, including cereal crops such as rice (Oryza sativa), wheat (Triticum aestivum), barley (Hordeum vulgare), maize (Zea mays), and sorghum (Sorghum bicolor; Zhou and Ibrahim, 2010). Commonly present as O-linked conjugates, tricin and its derivatives serve as allelochemicals (Kong et al, 2010) and insect deterrents (Ling et al, 2007).…”

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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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Tricin—a potential multifunctional nutraceutical

Cited by 111 publications

References 121 publications

Silencing CHALCONE SYNTHASE in Maize Impedes the Incorporation of Tricin into Lignin and Increases Lignin Content

Silencing CHALCONE SYNTHASE in Maize Impedes the Incorporation of Tricin into Lignin and Increases Lignin Content

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

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

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