Mutation in the Threonine Synthase Gene Results in an Over-Accumulation of Soluble Methionine in Arabidopsis

• Published in: Plant physiology (Bethesda) 2000-05, Vol.123 (1), p.101-110
• Main Authors: Derek Bartlem, Ingrid Lambein, Okamoto, Takashi, Itaya, Asuka, Yukie Uda, Kijima, Fumiko, Yuko Tamaki, Nambara, Eiji, Naito, Satoshi
• Format: Article
• Language: English
• Subjects: Accumulation; Amino Acid Sequence; Amino acids; Arabidopsis; Arabidopsis - enzymology; Arabidopsis - genetics; Arabidopsis - metabolism; Biochemistry; Biological and medical sciences; Biosynthesis; Carbon-Oxygen Lyases - genetics; cystathionine g-synthase; E coli; Enzymes; Fundamental and applied biological sciences. Psychology; Gene expression regulation; Genes. Genome; Genetic Complementation Test; Genetic mutation; Genetics, Genomics, and Molecular Evolution; Messenger RNA; Metabolism; Methionine - metabolism; Molecular and cellular biology; Molecular genetics; Molecular Sequence Data; mto2 gene; Mutation; Nitrogen metabolism; O-phosphohomoserine; Phenotypes; Plant physiology and development; Plants; Seedlings; Solubility
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.123.1.101

In higher plants, O-phosphohomoserine (OPH) represents a branch point between the methionine (Met) and threonine (Thr) biosynthetic pathways. It is believed that the enzymes Thr synthase (TS) and cystathionine γ-synthase (CGS) actively compete for the OPH substrate for Thr and Met biosynthesis, respectively. We have isolated a mutant of Arabidopsis, designated mto2-1, that over-accumulates soluble Met 22-fold and contains markedly reduced levels of soluble Thr in young rosettes. The mto2-1 mutant carries a single base pair mutation within the gene encoding TS, resulting in a leucine-204 to arginine change. Accumulation of TS mRNA and protein was normal in young rosettes of mto2-1, whereas functional complementation analysis of an Escherichia coli thrC mutation suggested that the ability of mto2-1 TS to synthesize Thr is impaired. We concluded that the mutation within the TS gene is responsible for the mto2-1 phenotype, resulting in decreased Thr biosynthesis and a channeling of OPH to Met biosynthesis in young rosettes. Analysis of the mto2-1 mutant suggested that, in vivo, the feedback regulation of CGS is not sufficient alone for the control of Met biosynthesis in young rosettes and is dependent on TS activity. In addition, developmental analysis of soluble Met and Thr concentrations indicated that the accumulation of these amino acids is regulated in a temporal and spatial manner.