Standing out from the crowd: Decoding the function of tau glutathione S-transferases GSTU24 and GSTU25 in Arabidopsis.

J. M. UGALDE, J. C. DÁVILA, A. J. MEYER

INRES-Chemical Signalling, University of Bonn, Friedrich-Ebert-Allee 144, D-53113 Bonn, Germany

Glutathione S-transferases (GSTs) are ubiquitous multifunctional enzymes that detoxify xenobiotics and toxic endogenous metabolites. Due to gene duplication in plants, GSTs are commonly arrayed in tandem or gene clusters, which increases the chance of functional redundancy and makes their characterization highly challenging. Arabidopsis has 53 GSTs grouped into seven classes, of which the plant-specific class tau (GSTU) is the largest. GSTUs have two GSH-dependent enzymatic activities: (1) GSH-binding to the electrophilic center of potentially toxic compounds (GST activity) and (2) a GSH-dependent peroxidase function towards lipid peroxides (GPOX activity). Among all GSTUs, GSTU24 and GSTU25 stand out with the highest GST and GPOX activities. Yet, their physiological role under oxidative stress is unknown. This work aims to dissect the critical functions of GSTU24 and GSTU25 under oxidative stress. As an experimental strategy, we generated variants of GSTU24 and GSTU25 affected in their GSH-dependent functions and evaluated them in a yeast strain deficient in GST activity and an Arabidopsis mutant lacking the transcription factors TGA2, TGA5, and TGA6, which is compromised in the expression of 12 GSTUs, including GSTU24 and GSTU25. The respective results provide valuable insight into the function of GSTs in plants and their potential applications in stress defense.