Thiol synthetases of legumes: immunogold localization and differential gene regulation by phytohormones

• Published in: Journal of experimental botany Vol. 63; no. 10; pp. 3923 - 3934
• Main Authors: Clemente, Maria R, Bustos-Sanmamed, Pilar, Loscos, Jorge, James, Euan K, Pérez-Rontomé, Carmen, Navascués, Joaquín, Gay, Marina, Becana, Manuel
• Format: Journal Article
• Language: English
• Published: Oxford Oxford University Press [etc.] 01.06.2012; Oxford University Press
• Subjects: Alfalfa; auxins; Biological and medical sciences; biosynthesis; chloroplasts; cytokinins; cytosol; electron microscopy; Enzymes; Fabaceae - chemistry; Fabaceae - enzymology; Fabaceae - genetics; Fundamental and applied biological sciences. Psychology; gene expression; gene expression regulation; Gene Expression Regulation, Enzymologic; Gene Expression Regulation, Plant; genes; glutamate-cysteine ligase; glutathione; glutathione synthase; homeostasis; homoglutathione synthase; Hormones; Immunohistochemistry; jasmonic acid; Leaves; Legumes; Ligases - chemistry; Ligases - genetics; Ligases - metabolism; Lotus corniculatus var. japonicus; Lotus japonicus; Messenger RNA; nitrogen; Nodules; plant development; Plant Growth Regulators - metabolism; plant hormones; Plant physiology and development; Plant Proteins - chemistry; Plant Proteins - genetics; Plant Proteins - metabolism; Plant roots; Plant Roots - chemistry; Plant Roots - enzymology; Plant Roots - genetics; Plants; polyamines; Protein Transport; RESEARCH PAPER; roots; salicylic acids; stress response; Sulfhydryl Compounds - metabolism; Thiols; Glutamate-cysteine ligase; Legumes; Immunogold labelling; Thiol; Carbon-nitrogen ligases; Enzyme; γ-Glutamylcysteine synthetase; Gene expression; Stress; Glutathione synthase; immunogold localization; Regulation(control); Gene; Ligases; Botany; Phytohormone; (homo)glutathione synthetase; plant stress; phytohormones
• ISSN: 0022-0957; 1460-2431
• DOI: 10.1093/jxb/ers083

In plants and other organisms, glutathione (GSH) biosynthesis is catalysed sequentially by γ-glutamylcysteine synthetase (γECS) and glutathione synthetase (GSHS). In legumes, homoglutathione (hGSH) can replace GSH and is synthesized by γECS and a specific homoglutathione synthetase (hGSHS). The subcellular localization of the enzymes was examined by electron microscopy in several legumes and gene expression was analysed in Lotus japonicus plants treated for 1–48 h with 50 μM of hormones. Immunogold localization studies revealed that γECS is confined to chloroplasts and plastids, whereas hGSHS is also in the cytosol. Addition of hormones caused differential expression of thiol synthetases in roots. After 24–48 h, abscisic and salicylic acids downregulated GSHS whereas jasmonic acid upregulated it. Cytokinins and polyamines activated GSHS but not γECS or hGSHS. Jasmonic acid elicited a coordinated response of the three genes and auxin induced both hGSHS expression and activity. Results show that the thiol biosynthetic pathway is compartmentalized in legumes. Moreover, the similar response profiles of the GSH and hGSH contents in roots of non-nodulated and nodulated plants to the various hormonal treatments indicate that thiol homeostasis is independent of the nitrogen source of the plants. The differential regulation of the three mRNA levels, hGSHS activity, and thiol contents by hormones indicates a fine control of thiol biosynthesis at multiple levels and strongly suggests that GSH and hGSH play distinct roles in plant development and stress responses.