Modifications in lignin and accumulation of phenolic glucosides in poplar xylem upon down-regulation of caffeoyl-coenzyme A O-methyltransferase, an enzyme involved in lignin biosynthesis.
Caffeoyl-coenzyme A O-methyltransferase (CCoAOMT) methylates, in vitro, caffeoyl-CoA and 5-hydroxyferuloyl-CoA, two possible precursors in monolignol biosynthesis in vivo. To clarify the in vivo role of CCoAOMT in lignin biosynthesis, transgenic poplars with 10% residual CCoAOMT protein levels in the stem xylem were generated. Upon analysis of the xylem, the affected transgenic lines had a 12% reduced Klason lignin content, an 11% increased syringyl/guaiacyl ratio in the noncondensed lignin fraction, and an increase in lignin-attached p-hydroxybenzoate but otherwise a lignin composition similar to that of wild type. Stem xylem of the CCoAOMT-down-regulated lines had a pink-red coloration, which coincided with an enhanced fluorescence of mature vessel cell walls. The reduced production of CCoAOMT caused an accumulation of O(3)-beta-d-glucopyranosyl-caffeic acid, O(4)-beta-d-glucopyranosyl-vanillic acid, and O(4)-beta-d-glucopyranosyl-sinapic acid (GSA), as authenticated by (1)H NMR. Feeding experiments showed that O(3)-beta-d-glucopyranosyl-caffeic acid and GSA are storage or detoxification products of caffeic and sinapic acid, respectively. The observation that down-regulation of CCoAOMT decreases lignin amount whereas GSA accumulates to 10% of soluble phenolics indicates that endogenously produced sinapic acid is not a major precursor in syringyl lignin biosynthesis. Our in vivo results support the recently obtained in vitro enzymatic data that suggest that the route from caffeic acid to sinapic acid is not used for lignin biosynthesis.
Meyermans
H
H
Vakgroep Moleculaire Genetica & Departement Plantengenetica, Vlaams Interuniversitair Instituut voor Biotechnologie, Universiteit Gent, B-9000 Gent, Belgium.
Morreel
K
K
Lapierre
C
C
Pollet
B
B
De Bruyn
A
A
Busson
R
R
Herdewijn
P
P
Devreese
B
B
Van Beeumen
J
J
Marita
J M
JM
Ralph
J
J
Chen
C
C
Burggraeve
B
B
Van Montagu
M
M
Messens
E
E
Boerjan
W
W
D000214:Acyl Coenzyme A / Q000378:metabolism; D002109:Caffeic Acids / Q000378:metabolism; D002236:Carbohydrate Conformation; D002851:Chromatography, High Pressure Liquid; D003373:Coumaric Acids / Q000737:chemistry; D015536:Down-Regulation; D005960:Glucosides / Q000378:metabolism*; D008031:Lignin / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D008780:Methyltransferases / Q000378:metabolism*; D008956:Models, Chemical; D010636:Phenols / Q000378:metabolism*; D010940:Plant Proteins / Q000378:metabolism*; D030821:Plants, Genetically Modified / Q000201:enzymology*; D014641:Vanillic Acid / Q000031:analogs & derivatives
C081711:4-O-beta-glucopyranosyl caffeic acid; D000214:Acyl Coenzyme A; D002109:Caffeic Acids; D003373:Coumaric Acids; D005960:Glucosides; D010636:Phenols; D010940:Plant Proteins; C058645:caffeoyl-coenzyme A; C090959:5-hydroxyferuloyl-coenzyme A; C073734:sinapinic acid; D008031:Lignin; D008780:Methyltransferases; C059825:caffeoyl-CoA O-methyltransferase; D014641:Vanillic Acid