A flavoprotein supports cell wall properties in the necrotrophic fungus Alternaria brassicicola

Sandrine Pigné,Muriel Marchi,Stéphane Cuenot,Guillaume N’Guyen,Etienne Janod,Agata Zykwinska,Guillaume Mabilleau,Mohammed Kerkoud,Thomas Guillemette,Nelly Bataillé-Simoneau,Anthony Kwasiborski,Roxane Raulo,Philippe Simoneau

doi:10.1186/s40694-016-0029-3

Abstract

BackgroundFlavin-dependent monooxygenases are involved in key biological processes as they catalyze a wide variety of chemo-, regio- and enantioselective oxygenation reactions. Flavoprotein monooxygenases are frequently encountered in micro-organisms, most of which require further functional and biocatalytic assessment. Here we investigated the function of the AbMak1 gene, which encodes a group A flavin monooxygenase in the plant pathogenic fungus Alternaria brassicicola, by generating a deficient mutant and examining its phenotype.ResultsFunctional analysis indicates that the AbMak1 protein is involved in cell wall biogenesis and influences the melanization process. We documented a significant decrease in melanin content in the Δabmak1 strain compared to the wild-type and complemented strains. We investigated the cell wall morphology and physical properties in the wild-type and transformants using electron and atomic force microscopy. These approaches confirmed the aberrant morphology of the conidial wall structure in the Δabmak1 strain which had an impact on hydrophilic adhesion and conidial surface stiffness. However, there was no significant impairment in growth, conidia formation, pathogenicity or susceptibility to various environmental stresses in the Δabmak1 strain.ConclusionThis study sheds new light on the function of a fungal flavin-dependent monooxygenase, which plays an important role in melanization.

Highlights

Flavin-dependent monooxygenases are involved in key biological processes as they catalyze a wide variety of chemo, regio- and enantioselective oxygenation reactions
In Alternaria brassicicola, we identified a gene encoding a class A flavin monooxygenase which was found to be upregulated by camalexin, the major phytoalexin produced by Arabidopsis thaliana [5]
AbMak1 encodes a class A flavoprotein monooxygenase The camalexin-induced sequence P1B3 (GenBank accession No DY543080) was previously identified in A. brassicicola as an EST encoding a predicted protein having matches with the flavin-containing monooxygenase MAK1 described in N. haematococca [5]

Summary

Introduction

Flavin-dependent monooxygenases are involved in key biological processes as they catalyze a wide variety of chemo-, regio- and enantioselective oxygenation reactions. Flavin-dependent monooxygenases are involved in a wide variety of biological processes, such as biosynthesis, catabolism and detoxification of various natural compounds and xenobiotics, in both prokaryotes and eukaryotes They catalyze the incorporation of one atom of molecular oxygen into the substrate and these oxygenation reactions include, for instance, hydroxylation, epoxidation, Baeyer–Villiger oxidation or sulfoxidation (for reviews, see [1,2,3]). Melanins constitute a group of related pigments that are polymers of phenolic compounds, the exact arrangement of these phenolic subunits is generally unclear [7] These ubiquitous pigments are known to provide protection against damaging effects of environmental stresses such as ultraviolet (UV) irradiation, enzymatic lysis, extreme temperatures, oxidizing agents and ionizing radiation [8]. They play a role in the pathogenesis of some human and plant pathogenic fungi [9, 10]

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