Identification and Characterization of Carboxylesterases from Brachypodium distachyon Deacetylating Trichothecene Mycotoxins.

Clemens Schmeitzl,Elisabeth Varga,Karl Kugler,Hans-Werner Mewes,Gerlinde Wiesenberger,Gerhard Adam,Herbert Michlmayr,Franz Berthiller,Rudolf Krska,Benedikt Warth,Rainer Schuhmacher,Alexandra Malachová,Klaus Mayer

doi:10.3390/toxins8010006

Abstract

Increasing frequencies of 3-acetyl-deoxynivalenol (3-ADON)-producing strains of Fusarium graminearum (3-ADON chemotype) have been reported in North America and Asia. 3-ADON is nearly nontoxic at the level of the ribosomal target and has to be deacetylated to cause inhibition of protein biosynthesis. Plant cells can efficiently remove the acetyl groups of 3-ADON, but the underlying genes are yet unknown. We therefore performed a study of the family of candidate carboxylesterases (CXE) genes of the monocot model plant Brachypodium distachyon. We report the identification and characterization of the first plant enzymes responsible for deacetylation of trichothecene toxins. The product of the BdCXE29 gene efficiently deacetylates T-2 toxin to HT-2 toxin, NX-2 to NX-3, both 3-ADON and 15-acetyl-deoxynivalenol (15-ADON) into deoxynivalenol and, to a lesser degree, also fusarenon X into nivalenol. The BdCXE52 esterase showed lower activity than BdCXE29 when expressed in yeast and accepts 3-ADON, NX-2, 15-ADON and, to a limited extent, fusarenon X as substrates. Expression of these Brachypodium genes in yeast increases the toxicity of 3-ADON, suggesting that highly similar genes existing in crop plants may act as susceptibility factors in Fusarium head blight disease.

Highlights

Brachypodium distachyon is a monocot grass species closely related to economically-important crops, like bread wheat (Triticum aestivum), barley (Hordeum vulgare) and rice (Oryza sativa)
We have recently shown that wheat cells are capable of efficiently deacetylating 3-ADON, 15-ADON and 3,15-diADON [14]
Assuming that either constitutively-expressed or toxin-inducible genes are candidates coding for active enzymes, we started to test the expression of a subset of 33 genes by semiquantitative real-time polymerase chain reaction (RT-PCR)

Summary

Introduction

Brachypodium distachyon is a monocot grass species closely related to economically-important crops, like bread wheat (Triticum aestivum), barley (Hordeum vulgare) and rice (Oryza sativa). F. graminearum species complex [6], F. graminearum and Fusarium asiaticum, can be grouped into so-called chemotypes depending on the trichothecene toxin they mainly produce in culture. Strains produce either nivalenol (NIV) or DON; the DON producers can be sub-grouped into 3-acetyl-DON (3-ADON) and 15-acetyl-DON (15-ADON) chemotypes. It has been shown that the allele of the carboxylesterase encoded by TRI8 determines which acetyl group is cleaved off from the common precursor 3,15-di-acetyl-DON, resulting in the production of 3-ADON or 15-ADON [7]. The NIV chemotype is determined by the allele of the TRI13 encoding a cytochrome P450 [8]. F. graminearum strains typically produce type B trichothecenes possessing a keto group at C8. A new chemotype was described (caused by an allele of TRI1) producing the NX-toxins, which lack a C8-keto group [9]

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