Molecular Genetic Analyzes of an Arabidopsis thaliana Mutant that Over-accumulates Soluble methionine.

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We have previously isolated an Arabidopsis thaliana mutant, mtol-1 that over-accumulates soluble methionine. The objectives of this research project is to disclose the mechanism of regulation of amino acid biosynthesis in higher plant by using the mtol-1 mutant. Northern analyzes indicated that the mRNA for cystathionine gamma-synthase gene was higher in the mutant than in wild-type plants. On the other hand, mRNA levels for cystathionine beta-lyase, methionine synthase (putative), and SAM syntheses are not appreciably affected by the mutation. Application of methionine from the root repressed the accumulation of cystathionine gamma-synthase mRNA in wild-type plants, while no such effect was evident in mtol-1 mutant plants. The results suggests that wild-type plants have a system to repress the level of cystathionine gamma-synthase mRNA and that the regulation system is impaired in the mtol mutant.Both the mtol mutation and cystathionine gamma-synthase gene mapped to the top region of chromosome 3, suggesting that the mtol mutation cases a cis mutation that affects either the transcription of cystathionine gamma-synthase gene of the stability of the mRNA.