title: Both caffeoyl Coenzyme A 3-O-methyltransferase 1 and caffeic acid O-methyltransferase 1 are involved in redundant functions for lignin, flavonoids and sinapoyl malate biosynthesis in Arabidopsis.
abstract: Two methylation steps are necessary for the biosynthesis of monolignols, the lignin precursors. Caffeic acid O-methyltransferase (COMT) O-methylates at the C5 position of the phenolic ring. COMT is responsible for the biosynthesis of sinapyl alcohol, the precursor of syringyl lignin units. The O-methylation at the C3 position of the phenolic ring involves the Caffeoyl CoA 3-O-methyltransferase (CCoAOMT). The CCoAOMT 1 gene (At4g34050) is believed to encode the enzyme responsible for the first O-methylation in Arabidopsis thaliana. A CCoAOMT1 promoter-GUS fusion and immunolocalization experiments revealed that this gene is strongly and exclusively expressed in the vascular tissues of stems and roots. An Arabidopsis T-DNA null mutant named ccomt 1 was identified and characterised. The mutant stems are slightly smaller than wild-type stems in short-day growth conditions and has collapsed xylem elements. The lignin content of the stem is low and the S/G ratio is high mainly due to fewer G units. These results suggest that this O-methyltransferase is involved in G-unit biosynthesis but does not act alone to perform this step in monolignol biosynthesis. To determine which O-methyltransferase assists CCoAOMT 1, a comt 1 ccomt1 double mutant was generated and studied. The development of comt 1 ccomt1 is arrested at the plantlet stage in our growth conditions. Lignins of these plantlets are mainly composed of p-hydroxyphenyl units. Moreover, the double mutant does not synthesize sinapoyl malate, a soluble phenolic. These results suggest that CCoAOMT 1 and COMT 1 act together to methylate the C3 position of the phenolic ring of monolignols in Arabidopsis. In addition, they are both involved in the formation of sinapoyl malate and isorhamnetin.
authors.affiliation: Biologie Cellulaire, INRA, 78026, Versailles cedex, France.
authors.forename: Cao-Trung
authors.initials: CT
authors.lastname: Do
authors.forename: Brigitte
authors.initials: B
authors.lastname: Pollet
authors.forename: Johanne
authors.initials: J
authors.lastname: Thévenin
authors.forename: Richard
authors.initials: R
authors.lastname: Sibout
authors.forename: Dominique
authors.initials: D
authors.lastname: Denoue
authors.forename: Yves
authors.initials: Y
authors.lastname: Barrière
authors.forename: Catherine
authors.initials: C
authors.lastname: Lapierre
authors.forename: Lise
authors.initials: L
authors.lastname: Jouanin
mesh_terms: D017360:Arabidopsis / Q000201:enzymology / Q000378:metabolism*; D001483:Base Sequence; D017931:DNA Primers; D005419:Flavonoids / Q000096:biosynthesis*; D008031:Lignin / Q000096:biosynthesis*; D008293:Malates / Q000378:metabolism*; D008780:Methyltransferases / Q000378:metabolism*; D010666:Phenylpropionates / Q000378:metabolism*; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: C079164:2-O-sinapoylmalate; D017931:DNA Primers; D005419:Flavonoids; D008293:Malates; D010666:Phenylpropionates; D008031:Lignin; D008780:Methyltransferases; C059825:caffeoyl-CoA O-methyltransferase; C019608:caffeate O-methyltransferase