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

• Published in: Planta Vol. 226; no. 5; pp. 1117 - 1129
• Main Authors: Do, Cao-Trung, Pollet, Brigitte, Thévenin, Johanne, Sibout, Richard, Denoue, Dominique, Barrière, Yves, Lapierre, Catherine, Jouanin, Lise
• Format: Journal Article
• Language: English
• Published: Berlin Berlin/Heidelberg : Springer-Verlag 01.10.2007; Springer-Verlag; Springer; Springer Nature B.V; Springer Verlag
• Subjects: Alcohols; Arabidopsis; Arabidopsis - enzymology; Arabidopsis - metabolism; Base Sequence; Biological and medical sciences; Biosynthesis; Caffeic acid O-methyltransferase; Caffeoyl CoA O-methyltransferase; DNA Primers; Enzymes; Flavonoids; Flavonoids - biosynthesis; Fundamental and applied biological sciences. Psychology; Genetics; Growth conditions; Life Sciences; Lignin; Lignin - biosynthesis; Malates - metabolism; Metabolism; Metabolism. Physicochemical requirements; Methylation; Methyltransferases - metabolism; Monomers; Mutants; Phenols; Phenylpropionates - metabolism; Plant physiology and development; Plant tissues; Plantlets; Plants; Plants genetics; Sinapoyl malate; Spectroscopy, Fourier Transform Infrared; Stems; T-DNA mutant; Xylem; Lignin; Enzyme; Arabidopsis; Transferases; Arabidopsis Caffeic acid O- methyltransferase; T-DNA mutant; Biosynthesis; Caffeic acid; Flavonoids; Lignin·Sinapoyl malate; Methyltransferases; Caffeoyl CoA 0-methyltransferase; Cruciferae; Dicotyledones; Angiospermae; Coenzyme A; Spermatophyta; Mutation; FLAVONOIDS; T-DNA MUTANT; ARABIDOPSIS; CAFFEOYL COA O-METHYLTRANSFERASE; CAFFEIC ACID O-METHYLTRANSFERASE; SINAPOYL MALATE; LIGNIN
• ISSN: 0032-0935; 1432-2048
• DOI: 10.1007/s00425-007-0558-3

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.