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

Abstract

SummaryAs an approach to understand the regulation of methionine (Met) metabolism, Arabidopsis Met overaccumulating 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.

Coordinated Genetic Regulation of Growth and Lignin Revealed by Quantitative Trait Locus Analysis of cDNA Microarray Data in an Interspecific Backcross of Eucalyptus

“…SAMS, HMT, and SAH are some of the most abundant ESTs found in cDNA libraries made from immature xylem tissue of loblolly pine undergoing compression wood formation (M. Kirst, unpublished data), a tissue with high lignin content relative to normal wood. The underexpression of SAMS has been shown to result in a decrease of lignin content in maize (Zea mays; Shen et al, 2002). The coordination of transcript profiles is consistent with the importance of the shikimate and Met pathways in lignin biosynthesis and suggests that transcription of many of the genes in these pathways are under a higher level of coordinated control.…”

“…Genetic mapping of candidate genes identified in this study revealed genetic colocalization of SAMS with growth and lignin gene expression QTLs. SAMS' role as the last enzyme in the synthesis of S-adenosylmethionine and its negative effect on the levels of lignin in transgenic maize plants (Shen et al, 2002) suggest that it is an important candidate for further analysis. SAMS may represent a rate-limiting step in lignin biosynthesis.…”

Network-based integration of systems genetics data reveals pathways associated with lignocellulosic biomass accumulation and processing

“…Several associations were identified (mainly with sugar release efficiency) for genes involved in cysteine and methionine metabolism, including ATCIMS/MS1. The roles of these genes in biomass formation are becoming increasingly revealed, being linked directly to either lignin (50,51) or hormone-mediated growth regulation (52). In addition, SCW polysaccharide biosynthesis genes known to be expressed in developing xylem (8) were mainly associated with variation in wood density and glucose release efficiency (Dataset S3).…”

ArabidopsisSAMT1 Defines a Plastid Transporter Regulating Plastid Biogenesis and Plant Development

“…Inactivation of Thr synthase leads to an imbalance in the regulation of the synthesis of aspartate-derived amino acids (Galili, 1995). Interestingly, even when the total concentration of SAM was increased or decreased in plant cells, plastid Thr synthase was not affected (Shen et al, 2002).…”