ABSTRACT
Plant glutathione transferases (GSTs) are induced by diverse biotic and abiotic stimuli, and are important for protecting plants against oxidative damage. We have studied the primary transcriptional stress response of the entire Arabidopsis GST family to seven stresses, including both biotic and abiotic stimuli, with a focus on early changes in gene expression. Our results indicate that individual GST genes are highly specific in their induction patterns. Furthermore, we have been able to link individual GSTs to particular stress stimuli. Using RNAi, we successfully co-silenced a group of four phi GSTs that represent some of the most highly expressed GST genes. Despite a marked reduction in total phi GST protein levels, the transgenic plants showed no reduction in GST activity as measured using the model substrate 1-chloro-2,4-dinitrobenzene (CDNB), and appeared to have surprisingly robust physical phenotypes during stress. However, analysis of metabolite pools showed oxidation of the glutathione pool in the RNAi lines, and we observed alterations in carbon and nitrogen compounds following salicylic acid and hydrogen peroxide stress treatments, indicative of oxidative modification of primary metabolism. Thus, there appears to be a high degree of functional redundancy within the Arabidopsis GST family, with extensive disruption being required to reveal the roles of phi GSTs in protection against oxidative stress.
