Wichadakul Duangdao, Kobmoo Noppol, Ingsriswang Supawadee, Tangphatsornruang Sithichoke, Chantasingh Duriya, Luangsa-ard Janet Jennifer, Eurwilaichitr Lily
National Center for Genetic Engineering and Biotechnology, National Science and Technology Development Agency, 113 Thailand Science Park, Phahonyothin Rd., Khlong Neung, Khlong Luang, 12120, Pathum Thani, Thailand.
Department of Computer Engineering, Faculty of Engineering, Chulalongkorn University, Floor 17th, Building 4, Payathai Rd., Wangmai, Pathumwan, 10330, Bangkok, Thailand.
BMC Genomics. 2015 Oct 28;16:881. doi: 10.1186/s12864-015-2101-4.
Ophiocordyceps unilateralis is an outstanding insect fungus for its biology to manipulate host ants' behavior and for its extreme host-specificity. Through the sequencing and annotation of Ophiocordyceps polyrhachis-furcata, a species in the O. unilateralis species complex specific to the ant Polyrhachis furcata, comparative analyses on genes involved in pathogenicity and virulence between this fungus and other fungi were undertaken in order to gain insights into its biology and the emergence of host specificity.
O. polyrhachis-furcata possesses various genes implicated in pathogenicity and virulence common with other fungi. Overall, this fungus possesses protein-coding genes similar to those found on other insect fungi with available genomic resources (Beauveria bassiana, Metarhizium robertsii (formerly classified as M. anisopliae s.l.), Metarhizium acridum, Cordyceps militaris, Ophiocordyceps sinensis). Comparative analyses in regard of the host ranges of insect fungi showed a tendency toward contractions of various gene families for narrow host-range species, including cuticle-degrading genes (proteases, carbohydrate esterases) and some families of pathogen-host interaction (PHI) genes. For many families of genes, O. polyrhachis-furcata had the least number of genes found; some genes commonly found in other insect fungi are even absent (e.g. Class 1 hydrophobin). However, there are expansions of genes involved in 1) the production of bacterial-like toxins in O. polyrhachis-furcata, compared with other entomopathogenic fungi, and 2) retrotransposable elements.
The gain and loss of gene families helps us understand how fungal pathogenicity in insect hosts evolved. The loss of various genes involved throughout the pathogenesis for O. unilateralis would result in a reduced capacity to exploit larger ranges of hosts and therefore in the different level of host specificity, while the expansions of other gene families suggest an adaptation to particular environments with unexpected strategies like oral toxicity, through the production of bacterial-like toxins, or sophisticated mechanisms underlying pathogenicity through retrotransposons.
单边蛇虫草菌是一种杰出的昆虫真菌，因其操纵宿主蚂蚁行为的生物学特性以及极强的宿主特异性而闻名。通过对叉齿多刺蚁蛇虫草菌（单边蛇虫草菌物种复合体中一种特定于叉齿多刺蚁的物种）进行测序和注释，对该真菌与其他真菌中涉及致病性和毒力的基因进行了比较分析，以便深入了解其生物学特性以及宿主特异性的产生。
叉齿多刺蚁蛇虫草菌拥有与其他真菌共有的多种涉及致病性和毒力的基因。总体而言，该真菌拥有与其他具有可用基因组资源的昆虫真菌（球孢白僵菌、罗伯茨绿僵菌（原分类为广义绿僵菌）、蝗绿僵菌、蛹虫草、中华被毛孢）中发现的蛋白质编码基因相似的基因。对昆虫真菌宿主范围的比较分析表明，包括角质层降解基因（蛋白酶、碳水化合物酯酶）和一些病原体 - 宿主相互作用（PHI）基因家族在内的各种基因家族，在宿主范围狭窄的物种中呈现出收缩的趋势。对于许多基因家族来说，叉齿多刺蚁蛇虫草菌中发现的基因数量最少；其他昆虫真菌中常见的一些基因甚至不存在（例如1类疏水蛋白）。然而，与其他昆虫病原真菌相比，叉齿多刺蚁蛇虫草菌中参与以下方面的基因有所扩增：1）类细菌毒素的产生；2）逆转座子。
基因家族的得失有助于我们理解昆虫宿主中真菌致病性是如何进化的。单边蛇虫草菌在整个致病过程中各种基因的丢失将导致其利用更广泛宿主的能力下降，从而导致宿主特异性水平的差异，而其他基因家族的扩增表明通过产生类细菌毒素等意外策略或通过逆转座子产生致病性的复杂机制来适应特定环境。
