Characterization of glutathione transferases involved in the pathogenicity of Alternaria brassicicola.

Benoit Calmes,Thomas Guillemette,Philippe Simoneau,Eric Gelhaye,Nelly Bataillé-Simoneau,Mélanie Morel-Rouhier

doi:10.1186/s12866-015-0462-0

Abstract

BackgroundGlutathione transferases (GSTs) represent an extended family of multifunctional proteins involved in detoxification processes and tolerance to oxidative stress. We thus anticipated that some GSTs could play an essential role in the protection of fungal necrotrophs against plant-derived toxic metabolites and reactive oxygen species that accumulate at the host-pathogen interface during infection.ResultsMining the genome of the necrotrophic Brassica pathogen Alternaria brassicicola for glutathione transferase revealed 23 sequences, 17 of which could be clustered into the main classes previously defined for fungal GSTs and six were ‘orphans’. Five isothiocyanate-inducible GSTs from five different classes were more thoroughly investigated. Analysis of their catalytic properties revealed that two GSTs, belonging to the GSTFuA and GTT1 classes, exhibited GSH transferase activity with isothiocyanates (ITC) and peroxidase activity with cumene hydroperoxide, respectively. Mutant deficient for these two GSTs were however neither more susceptible to ITC nor less aggressive than the wild-type parental strain. By contrast mutants deficient for two other GSTs, belonging to the Ure2pB and GSTO classes, were distinguished by their hyper-susceptibility to ITC and low aggressiveness against Brassica oleracea. In particular AbGSTO1 could participate in cell tolerance to ITC due to its glutathione-dependent thioltransferase activity. The fifth ITC-inducible GST belonged to the MAPEG class and although it was not possible to produce the soluble active form of this protein in a bacterial expression system, the corresponding deficient mutant failed to develop normal symptoms on host plant tissues.ConclusionsAmong the five ITC-inducible GSTs analyzed in this study, three were found essential for full aggressiveness of A. brassicicola on host plant. This, to our knowledge is the first evidence that GSTs might be essential virulence factors for fungal necrotrophs.Electronic supplementary materialThe online version of this article (doi:10.1186/s12866-015-0462-0) contains supplementary material, which is available to authorized users.

Highlights

Glutathione transferases (GSTs) represent an extended family of multifunctional proteins involved in detoxification processes and tolerance to oxidative stress
Our results indicate that three of these GSTs, belonging to the GSTO, Ure2pB and MAPEG classes, may contribute to pathogenicity probably by protecting the fungus against the oxidative stress generated by host plant defense compounds
Two sequences clustered close to P. chrysosporium GTT2, but their sequences contained domains related to beta or sigma GSTs that are usually found in bacteria and humans, respectively

Summary

Introduction

Glutathione transferases (GSTs) represent an extended family of multifunctional proteins involved in detoxification processes and tolerance to oxidative stress. This ligandin property has been defined as the capacity of the protein to bind non-substrate ligands [13] In plants, it could be involved in intracellular transport of hydrophobic compounds such as pigments, and in temporary storage of phytohormones [15, 16]. It could be involved in intracellular transport of hydrophobic compounds such as pigments, and in temporary storage of phytohormones [15, 16] In fungi, this ligandin property has been described for members of the GSTFuA class in P. chrysosporium [17]. In Saccharomyces pombe and Aspergillus fumigatus, GSTs are involved in the oxidative stress response Their gene expression is induced by hydrogen peroxide (H2O2). The GTT1 gene promoter contains specific regions of the response to xenobiotics [21] but GST regulation is usually the result of post-transcriptional modifications [22]

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Conclusion