title: Disrupting Flavone Synthase II Alters Lignin and Improves Biomass Digestibility.
abstract: Lignin, a ubiquitous phenylpropanoid polymer in vascular plant cell walls, is derived primarily from oxidative couplings of monolignols (p-hydroxycinnamyl alcohols). It was discovered recently that a wide range of grasses, including cereals, utilize a member of the flavonoids, tricin (3',5'-dimethoxyflavone), as a natural comonomer with monolignols for cell wall lignification. Previously, we established that cytochrome P450 93G1 is a flavone synthase II (OsFNSII) indispensable for the biosynthesis of soluble tricin-derived metabolites in rice (Oryza sativa). Here, our tricin-deficientfnsIImutant was analyzed further with an emphasis on its cell wall structure and properties. The mutant is similar in growth to wild-type control plants with normal vascular morphology. Chemical and nuclear magnetic resonance structural analyses demonstrated that the mutant lignin is completely devoid of tricin, indicating that FNSII activity is essential for the deposition of tricin-bound lignin in rice cell walls. The mutant also showed substantially reduced lignin content with decreased syringyl/guaiacyl lignin unit composition. Interestingly, the loss of tricin in the mutant lignin appears to be partially compensated by incorporating naringenin, which is a preferred substrate of OsFNSII. ThefnsIImutant was further revealed to have enhanced enzymatic saccharification efficiency, suggesting that the cell wall recalcitrance of grass biomass may be reduced through the manipulation of the flavonoid monomer supply for lignification.
authors.affiliation: School of Biological Sciences, The University of Hong Kong, Pokfulam, Hong Kong, China (P.Y.L., C.L.); and.|Research Institute for Sustainable Humanosphere (Y.To., Y.Ta., S.S., M.Y., T.U.) and Research Unit for Global Sustainability Studies (T.U.), Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan.
authors.forename: Pui Ying
authors.identifier: http://orcid.org/0000-0001-5025-1308
authors.initials: PY
authors.lastname: Lam
authors.affiliation: School of Biological Sciences, The University of Hong Kong, Pokfulam, Hong Kong, China (P.Y.L., C.L.); and ytobimatsu@rish.kyoto-u.ac.jp clivelo@hku.hk.|Research Institute for Sustainable Humanosphere (Y.To., Y.Ta., S.S., M.Y., T.U.) and Research Unit for Global Sustainability Studies (T.U.), Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan ytobimatsu@rish.kyoto-u.ac.jp clivelo@hku.hk.
authors.forename: Yuki
authors.identifier: http://orcid.org/0000-0002-7578-7392
authors.initials: Y
authors.lastname: Tobimatsu
authors.affiliation: School of Biological Sciences, The University of Hong Kong, Pokfulam, Hong Kong, China (P.Y.L., C.L.); and.|Research Institute for Sustainable Humanosphere (Y.To., Y.Ta., S.S., M.Y., T.U.) and Research Unit for Global Sustainability Studies (T.U.), Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan.
authors.forename: Yuri
authors.initials: Y
authors.lastname: Takeda
authors.affiliation: School of Biological Sciences, The University of Hong Kong, Pokfulam, Hong Kong, China (P.Y.L., C.L.); and.|Research Institute for Sustainable Humanosphere (Y.To., Y.Ta., S.S., M.Y., T.U.) and Research Unit for Global Sustainability Studies (T.U.), Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan.
authors.forename: Shiro
authors.identifier: http://orcid.org/0000-0002-6461-9844
authors.initials: S
authors.lastname: Suzuki
authors.affiliation: School of Biological Sciences, The University of Hong Kong, Pokfulam, Hong Kong, China (P.Y.L., C.L.); and.|Research Institute for Sustainable Humanosphere (Y.To., Y.Ta., S.S., M.Y., T.U.) and Research Unit for Global Sustainability Studies (T.U.), Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan.
authors.forename: Masaomi
authors.initials: M
authors.lastname: Yamamura
authors.affiliation: School of Biological Sciences, The University of Hong Kong, Pokfulam, Hong Kong, China (P.Y.L., C.L.); and.|Research Institute for Sustainable Humanosphere (Y.To., Y.Ta., S.S., M.Y., T.U.) and Research Unit for Global Sustainability Studies (T.U.), Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan.
authors.forename: Toshiaki
authors.identifier: http://orcid.org/0000-0003-1135-5387
authors.initials: T
authors.lastname: Umezawa
authors.affiliation: School of Biological Sciences, The University of Hong Kong, Pokfulam, Hong Kong, China (P.Y.L., C.L.); and ytobimatsu@rish.kyoto-u.ac.jp clivelo@hku.hk.|Research Institute for Sustainable Humanosphere (Y.To., Y.Ta., S.S., M.Y., T.U.) and Research Unit for Global Sustainability Studies (T.U.), Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan ytobimatsu@rish.kyoto-u.ac.jp clivelo@hku.hk.
authors.forename: Clive
authors.identifier: http://orcid.org/0000-0002-1995-3843
authors.initials: C
authors.lastname: Lo
mesh_terms: D018533:Biomass; D053898:Biosynthetic Pathways / Q000235:genetics; D002473:Cell Wall / Q000378:metabolism; D005298:Fertility / Q000235:genetics; D018506:Gene Expression Regulation, Plant; D055786:Gene Knockout Techniques; D017343:Genes, Plant; D008031:Lignin / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy; D006899:Mixed Function Oxygenases / Q000378:metabolism*; D009154:Mutation / Q000235:genetics; D012275:Oryza / Q000201:enzymology* / Q000235:genetics; D010641:Phenotype
chemical_list: D008031:Lignin; D006899:Mixed Function Oxygenases