High free-methionine and decreased lignin content result from a mutation in the Arabidopsis S-adenosyl-L-methionine synthetase 3 gene

Plant J. 2002 Feb;29(3):371-80. doi: 10.1046/j.1365-313x.2002.01221.x.


As an approach to understand the regulation of methionine (Met) metabolism, Arabidopsis Met over-accumulating mutants were isolated based on their resistance to selection by ethionine. One mutant, mto3, accumulated remarkably high levels of free Met - more than 200-fold that observed for wild type - yet showed little or no difference in the concentrations of other protein amino-acids, such as aspartate, threonine and lysine. Mutant plants did not show any visible growth differences compared with wild type, except a slight delay in germination. Genetic analysis indicated that the mto3 phenotype was caused by a single, recessive mutation. Positional cloning of this gene revealed that it was a novel S-adenosylmethionine synthetase, SAMS3. A point mutation resulting in a single amino-acid change in the ATP binding domain of SAMS3 was determined to be responsible for the mto3 phenotype. SAMS3 gene expression and total SAMS protein were not changed in mto3; however, both total SAMS activity and S-adenosylmethionine (SAM) concentration were decreased in mto3 compared with wild type. Lignin, a major metabolic sink for SAM, was decreased by 22% in mto3 compared with wild type, presumably due to the reduced supply of SAM. These results suggest that SAMS3 has a different function(s) in one carbon metabolism relative to the other members of the SAMS gene family.

Publication types

  • Comparative Study

MeSH terms

  • Arabidopsis / enzymology*
  • Arabidopsis / genetics
  • Chromosome Mapping
  • Cloning, Molecular / methods
  • Gene Expression Regulation, Enzymologic
  • Gene Expression Regulation, Plant
  • Genetic Complementation Test
  • Lignin / biosynthesis*
  • Methionine / metabolism*
  • Methionine Adenosyltransferase / genetics*
  • Methionine Adenosyltransferase / metabolism
  • Mutation
  • Phenotype
  • S-Adenosylmethionine / metabolism
  • Sequence Homology, Amino Acid


  • S-Adenosylmethionine
  • Lignin
  • Methionine
  • Methionine Adenosyltransferase