A new Arabidopsis thaliana mutant deficient in the expression of O-methyltransferase impacts lignins and sinapoyl esters.
A promoter-trap screen allowed us to identify an Arabidopsis line expressing GUS in the root vascular tissues. T-DNA border sequencing showed that the line was mutated in the caffeic acid O-methyltransferase 1 gene (AtOMT1) and therefore deficient in OMT1 activity. Atomt1 is a knockout mutant and the expression profile of the AtOMT1 gene has been determined as well as the consequences of the mutation on lignins, on soluble phenolics, on cell wall digestibility, and on the expression of the genes involved in monolignol biosynthesis. In this mutant and relative to the wild type, lignins lack syringyl (S) units and contain more 5-hydroxyguaiacyl units (5-OH-G), the precursors of S-units. The sinapoyl ester pool is modified with a two-fold reduction of sinapoyl-malate in the leaves and stems of mature plants as well as in seedlings. In addition, LC-MS analysis of the soluble phenolics extracted from the seedlings reveals the occurrence of unusual derivatives assigned to 5-OH-feruloyl malate and to 5-OH-feruloyl glucose. Therefore, AtOMT1 enzymatic activity appears to be involved not only in lignin formation but also in the biosynthesis of sinapate esters. In addition, a deregulation of other monolignol biosynthetic gene expression can be observed in the Atomt1 mutant. A poplar cDNA encoding a caffeic acid OMT (PtOMT1) was successfully used to complement the Atomt1 mutant and restored both the level of S units and of sinapate esters to the control level. However, the over-expression of PtOMT1 in wild-type Arabidopsis did not increase the S-lignin content, suggesting that OMT is not a limiting enzyme for S-unit biosynthesis.
Goujon
Thomas
T
Biologie cellulaire, INRA, 78026 Versailles Cedex, France.
Sibout
Richard
R
Pollet
Brigitte
B
Maba
Bruno
B
Nussaume
Laurent
L
Bechtold
Nicole
N
Lu
Fachuang
F
Ralph
John
J
Mila
Isabelle
I
Barrière
Yves
Y
Lapierre
Catherine
C
Jouanin
Lise
L
D000429:Alcohol Oxidoreductases / Q000235:genetics; D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism; D029681:Arabidopsis Proteins; D002473:Cell Wall / Q000378:metabolism; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics; D004952:Esters; D005419:Flavonoids / Q000378:metabolism; D035264:Flowers / Q000235:genetics / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D005816:Genetic Complementation Test; D008031:Lignin / Q000096:biosynthesis*; D008780:Methyltransferases / Q000235:genetics* / Q000378:metabolism; D006899:Mixed Function Oxygenases / Q000235:genetics; D009154:Mutation; D010802:Phylogeny; D018547:Plant Stems / Q000235:genetics / Q000378:metabolism; D032107:Populus / Q000201:enzymology / Q000235:genetics; D012995:Solubility
D029681:Arabidopsis Proteins; D004952:Esters; D005419:Flavonoids; D008031:Lignin; D003577:Cytochrome P-450 Enzyme System; D006899:Mixed Function Oxygenases; D000429:Alcohol Oxidoreductases; C018656:cinnamyl alcohol dehydrogenase; C097486:CYP84A1 protein, Arabidopsis; D008780:Methyltransferases; C059825:caffeoyl-CoA O-methyltransferase; C019608:caffeate O-methyltransferase