title: High free-methionine and decreased lignin content result from a mutation in the Arabidopsis S-adenosyl-L-methionine synthetase 3 gene.
abstract: 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.
authors.affiliation: Pioneer Hi-Bred International, Inc., 7300 NW 62nd Avenue, Johnston, Iowa, USA.
authors.forename: Bo
authors.initials: B
authors.lastname: Shen
authors.forename: Changjiang
authors.initials: C
authors.lastname: Li
authors.forename: Mitchell C
authors.initials: MC
authors.lastname: Tarczynski
mesh_terms: D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics; D002874:Chromosome Mapping; D003001:Cloning, Molecular / Q000379:methods; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D005816:Genetic Complementation Test; D008031:Lignin / Q000096:biosynthesis*; D008715:Methionine / Q000378:metabolism*; D008716:Methionine Adenosyltransferase / Q000235:genetics* / Q000378:metabolism; D009154:Mutation; D010641:Phenotype; D012436:S-Adenosylmethionine / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
chemical_list: D012436:S-Adenosylmethionine; D008031:Lignin; D008715:Methionine; D008716:Methionine Adenosyltransferase