Journal
COMPTES RENDUS DE L ACADEMIE DES SCIENCES SERIE III-SCIENCES DE LA VIE-LIFE SCIENCES
Volume 323, Issue 10, Pages 841-851Publisher
EDITIONS SCIENTIFIQUES MEDICALES ELSEVIER
DOI: 10.1016/S0764-4469(00)01242-7
Keywords
Arabidopsis thaliana; essential amino acids; methionine; transgenic plants; cystathionine gamma-synthase
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To investigate the role of cystathionine gamma -synthase (CGS) in the regulation of methionine synthesis Arabidopsis plants were transformed with a full-length antisense CGS cDNA and transformants analysed. Plants that were heterozygous for the transgene showed a 20-fold reduction of CCS activity that was accompanied by severe growth retardation and morphological abnormalities, from germination to flowering. Application of exogenous methionine to the transgenic lines restored normal growth. Surprisingly, transformed Arabidopsis plants exhibited a modest decrease in methionine content (35% reduction of the wild-type level) but a seven-fold decrease in the soluble pool of S-methylmethionine (SMM), a compound that plays a major role in storage and transport of reduced sulphur and labile methyl moieties. Several mechanisms can account for the maintenance of the soluble pool of methionine. First, the observed 20-fold increase in O-phosphohomoserine, a substrate of CGS, could compensate for the depressed level of CGS polypeptide by increasing the net rate of catalysis supported by the remaining enzyme. Second, the transgenic plants exhibited a two-fold increased level of cystathionine beta -lyase, the second enzyme in the methionine biosynthetic pathway. This indicates that enzymes other than CGS are subjected to a regulatory control by methionine or one of its metabolites. In addition to these mechanisms affecting de novo methionine synthesis, the recruitment of SMM to produce methionine may account for the small change of methionine levels in transgenic lines. (C) 2000 Academie des sciences/Editions scientifiques et medicales Elsevier SAS.
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