Caffeoyl coenzyme A O-methyltransferase down-regulation is associated with modifications in lignin and cell-wall architecture in flax secondary xylem.
Caffeoyl coenzyme A O-methyltransferase (CCoAOMT, EC 2.1.1.104) down-regulated-flax (Linum usitatissimum) plants were generated using an antisense strategy and functionally characterized. Chemical analyses (acetyl bromide and thioacidolysis) revealed that the lignin quantity was reduced and that the Syringyl/Guaïacyl (S/G) lignin monomer ratio was modified in the non-condensed lignin fraction of two independent down-regulated lines. These modifications were associated with altered xylem organization (both lines), reduced cell-wall thickness (one line) and the appearance of an irregular xylem (irx) phenotype (both lines). In addition UV microspectroscopy also indicated that CCoAOMT down-regulation induced changes in xylem cell-wall structure and the lignin fractions. Microscopic examination also suggested that CCoAOMT down-regulation could influence individual xylem cell size and identity. As a first step towards investigating the cellular mechanisms responsible for the unusual structure of flax lignin (G-rich, condensed), recombinant flax CCoAOMT protein was produced and its affinity for different potential substrates evaluated. Results indicated that the preferred substrate was caffeoyl coenzyme A, followed by 5-hydroxyconiferaldehyde suggesting that flax CCoAOMT possesses a small, but probably significant 5' methylating activity, in addition to a more usual 3' methylating activity.
Day
Arnaud
A
Université Lille 1, F-59655 Villeneuve d'Ascq, France.
Neutelings
Godfrey
G
Nolin
Frédérique
F
Grec
Sébastien
S
Habrant
Anouk
A
Crônier
David
D
Maher
Bouchra
B
Rolando
Christian
C
David
Hélène
H
Chabbert
Brigitte
B
Hawkins
Simon
S
D000595:Amino Acid Sequence; D002473:Cell Wall; D018076:DNA, Complementary; D015536:Down-Regulation / Q000502:physiology; D019597:Flax / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics; D008031:Lignin / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008780:Methyltransferases / Q000235:genetics / Q000378:metabolism*; D015591:Microspectrophotometry; D008969:Molecular Sequence Data; D010802:Phylogeny; D030821:Plants, Genetically Modified; D016415:Sequence Alignment; D052584:Xylem / Q000166:cytology*
D018076:DNA, Complementary; D008031:Lignin; D008780:Methyltransferases; C059825:caffeoyl-CoA O-methyltransferase