Compensation of Mutation in Arabidopsis glutathione transferase (AtGSTU) Genes under Control or Salt Stress Conditions.

Edit Horváth,Riyazuddin Riyazuddin,Dorottya Csenki,Gábor Csomor,Jolán Csiszár,Ágnes Gallé,Krisztina Bela

doi:10.3390/ijms21072349

Abstract

Glutathione transferases (GSTs) play a crucial role in detoxification processes due to the fact of their glutathione (GSH) conjugating activity, and through glutathione peroxidase or dehydroascorbate reductase (DHAR) activities, they influence the redox state of GSH and ascorbate (AsA). The plant-specific tau (GSTU) group is the largest class of Arabidopsis GSTs, and their members are involved in responses to different abiotic stresses. We investigated the effect of salt stress on two-week-old Arabidopsis thaliana wild-type (Col-0), Atgstu19 and Atgstu24 mutant plants after applying 150 mM NaCl for two days. The Atgstu19 seedlings had lower GST activity and vitality both under control conditions and after salt stress than the wild-type, but the level of total ROS was similar to the Col-0 plants. The GST activity of the knockout Atgstu24 mutant was even higher under control conditions compared to the Col-0 plants, while the ROS level and its vitality did not differ significantly from the wild-type. Analysis of the AtGSTU expression pattern revealed that the mutation in a single AtGSTU gene was accompanied by the up- and downregulation of several other AtGSTUs. Moreover, elevated AsA and GSH levels, an altered GSH redox potential and increased DHAR and glutathione reductase activities could help to compensate for the mutation of AtGSTU genes. The observed changes in the mutants suggest that the investigated isoenzymes influence the redox homeostasis under control conditions and after NaCl treatment in Arabidopsis seedlings. These data indicate for the first time the more general role of a temporary shift of redox status as part of GST mechanisms and regulation.

Highlights

Glutathione transferases (GSTs) belong to a very ancient protein superfamily that is thought to have evolved in response to the development of oxidative stress
In the search for clues to understand the role of AtGSTU19 and AtGSTU24 in defence against salt stress, we focused our attention on the changes after 48 h of the 150 mM NaCl treatment of two-week-old A. thaliana plants
Correlating well with the results of earlier studies [26], we found that knockdown mutation of the AtGSTU19 gene resulted in decreased GST activity and vitality, both under control conditions and after applying 150 mM NaCl (49% in roots compared to salt-treated Col-0), but the level of total reactive oxygen species (ROS) was even lower than in the wild-type

Summary

Introduction

Glutathione transferases (GSTs) belong to a very ancient protein superfamily that is thought to have evolved in response to the development of oxidative stress. Plant genomes contain dozens of GST genes and most of the proteins can be found in homodimer or heterodimer form, leading to enormous diversity within GST protein families [1] Glutathione transferases function both as catalytic enzymes with activity towards various substrates as well as non-catalytic, binding and carrier proteins [2,3]. Tau and phi GSTs are involved mainly in xenobiotic metabolism, which may be related to their high affinity toward a broad spectrum of harmful compounds, including xenobiotics and endogenous stress metabolites They have detectable glutathione-conjugating activity towards standard xenobiotic GST substrates, but via their glutathione peroxidase (GPOX) activity, they may take part in reducing the levels of H2O2 and other peroxides [5]. By using glutathione (GSH, γ-Glu-Cys-Gly) as a co-substrate, their catalytic activity may reduce the pool of this redox-active molecule

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