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 “yeast-like” 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 (ΔZtGT2) suggested the protein functions to maintain the outermost surface of the fungal cell wall. Despite this, adhesion to leaf surfaces was unaffected in ΔZtGT2 mutants and global RNAseq-based gene expression profiling highlighted that surface-sensing and protein secretion was also largely unaffected. However, ΔZtGT2 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.

致病真菌必须在整个固体表面上延伸丝状菌丝，以引起植物病害。但是，支持这一功能的基因的完整清单尚不完整，由于它们对菌丝生长形式的重要性，目前可能隐藏了许多基因。在一个随机的T-DNA诱变屏幕上的多形性小麦进行（普通小麦）病原体Zymoseptoria小麦，我们获得了一个突变体，该突变体不能在固体表面上专门延伸菌丝。相反，“类酵母”生长和所有其他生长形式均不受影响。无法扩展表面菌丝导致植物完全丧失毒力。受影响的基因编码预测的2型糖基转移酶（ZtGT2）。对来自分类学上不同的真菌的800多个基因组的分析突显了ZtGT2直向同源物普遍分布但不连续的分布，并且在无丝状子囊酵母中完全没有任何相似的蛋白质。分类学上不相关的真菌镰刀镰刀菌中ZtGT2直向同源物的缺失突变体也严重损害了麦穗的菌丝生长和非致病性。ZtGT2在丝状生长过程中表达增加，缺失突变体（ΔZtGT2）的电子显微镜表明该蛋白具有维持真菌细胞壁最外层表面的功能。尽管如此，在ΔZtGT2突变体中对叶片表面的附着力并没有受到影响，基于全局RNAseq的基因表达谱分析表明，表面感应和蛋白质分泌也基本上没有受到影响。但是，ΔZtGT2突变体组成性地过表达了几种跨膜和分泌的蛋白质，包括重要的LysM域几丁质结合毒力效应子Zt3LysM。ZtGT2可能在目前未知，可能较小但分布广泛的细胞外或细胞外多糖的合成中起作用，该多糖通过使菌丝在固体基质上生长，在促进植物与真菌之间的许多相互作用中起关键作用。