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

TitleCompletion of Tricin Biosynthesis Pathway in Rice: Cytochrome P450 75B4 Is a Unique Chrysoeriol 5′-Hydroxylase
Authors
Issue Date2015
PublisherAmerican Society of Plant Biologists. The Journal's web site is located at http://www.plantphysiol.org
Citation
Plant Physiology, 2015, v. 168 n. 4, p. 1527-1536 How to Cite?
AbstractFlavones 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 3′,5′-dimethoxyflavone nucleus is formed before O-linked conjugations. Previously, flavonoid 3′,5′-hydroxylases belonging to the CYP75A subfamily were believed to generate tricetin from apigenin for 3′,5′-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 3′-methoxylated flavone). CYP75B4 functions as a bona fide flavonoid 3′-hydroxylase by restoring the accumulation of 3′-hydroxylated flavonoids in Arabidopsis (Arabidopsis thaliana) transparent testa7 mutants and catalyzing in vitro 3′-hydroxylation of different flavonoids. In addition, overexpression of both CYP75B4 and CYP93G1 (a flavone synthase II) in Arabidopsis resulted in tricin accumulation. Specific 5′-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 3′-hydroxylase sequences. Recruitment of chrysoeriol-specific 5′-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.
Persistent Identifierhttp://hdl.handle.net/10722/211598
ISSN
2019 Impact Factor: 6.902
2015 SCImago Journal Rankings: 3.642
PubMed Central ID
ISI Accession Number ID

 

DC FieldValueLanguage
dc.contributor.authorLam, PY-
dc.contributor.authorLiu, H-
dc.contributor.authorLo, CSC-
dc.date.accessioned2015-07-21T02:04:13Z-
dc.date.available2015-07-21T02:04:13Z-
dc.date.issued2015-
dc.identifier.citationPlant Physiology, 2015, v. 168 n. 4, p. 1527-1536-
dc.identifier.issn0032-0889-
dc.identifier.urihttp://hdl.handle.net/10722/211598-
dc.description.abstractFlavones 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 3′,5′-dimethoxyflavone nucleus is formed before O-linked conjugations. Previously, flavonoid 3′,5′-hydroxylases belonging to the CYP75A subfamily were believed to generate tricetin from apigenin for 3′,5′-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 3′-methoxylated flavone). CYP75B4 functions as a bona fide flavonoid 3′-hydroxylase by restoring the accumulation of 3′-hydroxylated flavonoids in Arabidopsis (Arabidopsis thaliana) transparent testa7 mutants and catalyzing in vitro 3′-hydroxylation of different flavonoids. In addition, overexpression of both CYP75B4 and CYP93G1 (a flavone synthase II) in Arabidopsis resulted in tricin accumulation. Specific 5′-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 3′-hydroxylase sequences. Recruitment of chrysoeriol-specific 5′-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.-
dc.languageeng-
dc.publisherAmerican Society of Plant Biologists. The Journal's web site is located at http://www.plantphysiol.org-
dc.relation.ispartofPlant Physiology-
dc.titleCompletion of Tricin Biosynthesis Pathway in Rice: Cytochrome P450 75B4 Is a Unique Chrysoeriol 5′-Hydroxylase-
dc.typeArticle-
dc.identifier.emailLo, CSC: clivelo@hku.hk-
dc.identifier.authorityLo, CSC=rp00751-
dc.description.naturelink_to_OA_fulltext-
dc.identifier.doi10.1104/pp.15.00566-
dc.identifier.pmid26082402-
dc.identifier.pmcidPMC4528758-
dc.identifier.scopuseid_2-s2.0-84939154773-
dc.identifier.hkuros244697-
dc.identifier.volume168-
dc.identifier.issue4-
dc.identifier.spage1527-
dc.identifier.epage1536-
dc.identifier.isiWOS:000359317400030-
dc.publisher.placeUnited States-

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