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A conserved fungal glycosyltransferase facilitates pathogenesis of plants by enabling hyphal growth on solid surfaces
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Pathogenic fungi must extend filamentous hyphae across solid surfaces to cause diseases of plants. However, the full inventory of genes which support this is incomplete and many may be currently concealed due to their essentiality for the hyphal growth form. During a random T-DNA mutagenesis screen performed on the pleomorphic wheat (Triticum aestivum) pathogen Zymoseptoria tritici, we acquired a mutant unable to extend hyphae specifically when on solid surfaces. In contrast âyeast-likeâ growth, and all other growth forms, were unaffected. The inability to extend surface hyphae resulted in a complete loss of virulence on plants. The affected gene encoded a predicted type 2 glycosyltransferase (ZtGT2). Analysis of >800 genomes from taxonomically diverse fungi highlighted a generally widespread, but discontinuous, distribution of ZtGT2 orthologues, and a complete absence of any similar proteins in non-filamentous ascomycete yeasts. Deletion mutants of the ZtGT2 orthologue in the taxonomically un-related fungus Fusarium graminearum were also severely impaired in hyphal growth and non-pathogenic on wheat ears. ZtGT2 expression increased during filamentous growth and electron microscopy on deletion mutants (ÎZtGT2) suggested the protein functions to maintain the outermost surface of the fungal cell wall. Despite this, adhesion to leaf surfaces was unaffected in ÎZtGT2 mutants and global RNAseq-based gene expression profiling highlighted that surface-sensing and protein secretion was also largely unaffected. However, ÎZtGT2 mutants constitutively overexpressed several transmembrane and secreted proteins, including an important LysM-domain chitin-binding virulence effector, Zt3LysM. ZtGT2 likely functions in the synthesis of a currently unknown, potentially minor but widespread, extracellular or outer cell wall polysaccharide which plays a key role in facilitating many interactions between plants and fungi by enabling hyphal growth on solid matrices
The Induction of Mycotoxins by Trichothecene Producing Fusarium Species
In recent years, many Fusarium species have emerged which now threaten the productivity and safety of small grain cereal crops worldwide. During floral infection and post-harvest on stored grains the Fusarium hyphae produce various types of harmful mycotoxins which subsequently contaminate food and feed products. This article focuses specifically on the induction and production of the type B sesquiterpenoid trichothecene mycotoxins. Methods are described which permit in liquid culture the small or large scale production and detection of deoxynivalenol (DON) and its various acetylated derivatives. A wheat (Triticum aestivum L.) ear inoculation assay is also explained which allows the direct comparison of mycotoxin production by species, chemotypes and strains with different growth rates and/or disease-causing abilities. Each of these methods is robust and can be used for either detailed time-course studies or end-point analyses. Various analytical methods are available to quantify the levels of DON, 3A-DON and 15A-DON. Some criteria to be considered when making selections between the different analytical methods available are briefly discussed