Quandt C Alisha, Di Yanming, Elser Justin, Jaiswal Pankaj, Spatafora Joseph W
Department of Botany and Plant Pathology, Oregon State University, Corvallis, Oregon, 97331
Department of Statistics, Oregon State University, Corvallis, Oregon, 97331.
G3 (Bethesda). 2016 Jan 22;6(3):731-41. doi: 10.1534/g3.116.027045.
The ability of a fungus to infect novel hosts is dependent on changes in gene content, expression, or regulation. Examining gene expression under simulated host conditions can explore which genes may contribute to host jumping. Insect pathogenesis is the inferred ancestral character state for species of Tolypocladium, however several species are parasites of truffles, including Tolypocladium ophioglossoides. To identify potentially crucial genes in this interkingdom host switch, T. ophioglossoides was grown on four media conditions: media containing the inner and outer portions of its natural host (truffles of Elaphomyces), cuticles from an ancestral host (beetle), and a rich medium (Yeast Malt). Through high-throughput RNASeq of mRNA from these conditions, many differentially expressed genes were identified in the experiment. These included PTH11-related G-protein-coupled receptors (GPCRs) hypothesized to be involved in host recognition, and also found to be upregulated in insect pathogens. A divergent chitinase with a signal peptide was also found to be highly upregulated on media containing truffle tissue, suggesting an exogenous degradative activity in the presence of the truffle host. The adhesin gene, Mad1, was highly expressed on truffle media as well. A BiNGO analysis of overrepresented GO terms from genes expressed during each growth condition found that genes involved in redox reactions and transmembrane transport were the most overrepresented during T. ophioglossoides growth on truffle media, suggesting their importance in growth on fungal tissue as compared to other hosts and environments. Genes involved in secondary metabolism were most highly expressed during growth on insect tissue, suggesting that their products may not be necessary during parasitism of Elaphomyces. This study provides clues into understanding genetic mechanisms underlying the transition from insect to truffle parasitism.
真菌感染新宿主的能力取决于基因含量、表达或调控的变化。在模拟宿主条件下检查基因表达可以探索哪些基因可能有助于宿主跳跃。昆虫致病是拟青霉属物种推测的祖先性状状态，然而有几个物种是块菌的寄生虫，包括嗜蓝孢孔菌。为了确定这种跨界宿主转换中潜在的关键基因，嗜蓝孢孔菌在四种培养基条件下生长：含有其天然宿主（大团囊菌块菌）内部和外部的培养基、来自祖先宿主（甲虫）的角质层以及丰富培养基（酵母麦芽培养基）。通过对这些条件下mRNA的高通量RNA测序，在实验中鉴定出许多差异表达基因。这些基因包括推测参与宿主识别且在昆虫病原体中也上调的与PTH11相关的G蛋白偶联受体（GPCR）。还发现一种带有信号肽的不同的几丁质酶在含有块菌组织的培养基上高度上调，这表明在块菌宿主存在时具有外源性降解活性。黏附素基因Mad1在块菌培养基上也高度表达。对每个生长条件下表达的基因中过度富集的GO术语进行的BiNGO分析发现，参与氧化还原反应和跨膜运输的基因在嗜蓝孢孔菌在块菌培养基上生长期间过度富集最多，这表明它们在真菌组织上生长相对于其他宿主和环境的重要性。参与次生代谢的基因在昆虫组织上生长期间表达最高，这表明它们的产物在大团囊菌寄生期间可能不是必需的。这项研究为理解从昆虫寄生到块菌寄生转变的遗传机制提供了线索。
