Constitutive Overexpression of Cystathionine γ-Synthase in Arabidopsis Leads to Accumulation of Soluble Methionine and S-Methylmethionine

• Published in: Plant physiology (Bethesda) 2002-01, Vol.128 (1), p.95-107
• Main Authors: Kim, Jungsup, Minsang Lee, Radhika Chalam, Melinda Neal Martin, Leustek, Thomas, Boerjan, Wout
• Format: Article
• Language: English
• Subjects: Amino acids; Arabidopsis - enzymology; Arabidopsis - genetics; Arabidopsis - growth & development; Arabidopsis thaliana; Biochemical Processes and Macromolecular Structures; Biological and medical sciences; Carbon-Oxygen Lyases - genetics; Carbon-Oxygen Lyases - metabolism; cystathionine ^g-synthase; Enzymes; ethionine; Ethionine - pharmacology; Flowers; Fruit - enzymology; Fruit - genetics; Fruit - growth & development; Fundamental and applied biological sciences. Psychology; Gene Expression Regulation; Gene Silencing; Immunoblotting; Leaves; Metabolism; Methionine - biosynthesis; Methionine - pharmacology; Mutation; Nitrogen metabolism; Plant growth; Plant morphology; Plant physiology and development; Plant roots; Plant Roots - enzymology; Plant Roots - genetics; Plant Roots - growth & development; Plant Shoots - enzymology; Plant Shoots - genetics; Plant Shoots - growth & development; Plant Structures - enzymology; Plant Structures - genetics; Plant Structures - growth & development; Plants; Plants, Genetically Modified; RNA; S-Adenosylmethionine - biosynthesis; Threonine - biosynthesis; Transcription, Genetic - genetics; Transgenic plants; Up-Regulation; Vitamin U - biosynthesis
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.101801

The committing step in Met and S-adenosyl-L-Met (SAM) synthesis is catalyzed by cystathionine γ-synthase (CGS). Transgenic Arabidopsis plants overexpressing CGS under control of the cauliflower mosaic virus 35S promoter show increased soluble Met and its metabolite S-methyl-Met, but only at specific stages of development. The highest level of Met and S-methyl-Met was observed in seedling tissues and in flowers, siliques, and roots of mature plants where they accumulate 8- to 20-fold above wild type, whereas the level in mature leaves and other tissues is no greater than wild type. CGS-overexpressing seedlings are resistant to ethionine, a toxic Met analog. With these properties the transgenic lines resemble mto1, an Arabidopsis, CGS-mutant inactivated in the autogenous control mechanism for Met-dependent down-regulation of CGS expression. However, wild-type CGS was overexpressed in the transgenic plants, indicating that autogenous control can be overcome by increasing the level of CGS mRNA through transcriptional control. Several of the transgenic lines show silencing of CGS resulting in deformed plants with a reduced capacity for reproductive growth. Exogenous feeding of Met to the most severely affected plants partially restores their growth. Similar morphological deformities are observed in plants cosuppressed for SAM synthetase, even though such plants accumulate 250-fold more soluble Met than wild type and they overexpress CGS. The results suggest that the abnormalities associated with CGS and SAM synthetase silencing are due in part to a reduced ability to produce SAM and that SAM may be a regulator of CGS expression.