Probing the diversity of the arabidopsis glutathione S-transferase gene family

Glutathione S-transferases (GSTs) appear to be ubiquitous in plants and have defined roles in herbicide detoxification. In contrast, little is known about their roles in normal plant physiology and during responses to biotic and abiotic stress. Forty-seven members of the GST super-family were identified in the Arabidopsis genome, grouped into four classes, with amino acid sequence identity between classes being below 25%. The two small zeta (GSTZ) and theta (GSTT) classes have related GSTs in animals while the large phi (GSTF) and tau (GSTU) classes are plant specific. As a first step to functionally characterize this diverse super-family, 10 cDNAs representing all GST classes were cloned by RT-PCR and used to study AtGST expression in response to treatment with phytohormones, herbicides, oxidative stress and inoculation with virulent and avirulent strains of the downy mildew pathogen Peronospora parasitica. The abundance of transcripts encoding AtGSTF9, AtGSTF10, AtGSTU5, AtGSTU13 and AtGSTT1 were unaffected by any of the treatments. In contrast, AtGSTF6 was upregulated by all treatments while AtGSTF2, AtGSTF8, AtGSTU19 and AtGSTZ1 each showed a selective spectrum of inducibility to the different stresses indicating that regulation of gene expression in this super-family is controlled by multiple mechanisms. The respective cDNAs were over expressed in E. coli. All GSTs except AtGSTF10 formed soluble proteins which catalysed a specific range of glutathione conjugation or glutathione peroxidase activities. Our results give further insights into the complex regulation and enzymic functions of this plant gene super-family.