Insights from the genome of Ophiocordyceps polyrhachis-furcata to pathogenicity and host specificity in insect fungi.
BACKGROUND
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.


RESULTS
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.


CONCLUSIONS
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.
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. duangdao.w@chula.ac.th.|Department of Computer Engineering, Faculty of Engineering, Chulalongkorn University, Floor 17th, Building 4, Payathai Rd., Wangmai, Pathumwan, 10330, Bangkok, Thailand. duangdao.w@chula.ac.th.
Duangdao
D
Wichadakul
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. noppol.kob@biotec.or.th.
Noppol
N
Kobmoo
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. supawadee@biotec.or.th.
Supawadee
S
Ingsriswang
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. sithichoke.tan@biotec.or.th.
Sithichoke
S
Tangphatsornruang
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. Duriya@biotec.or.th.
Duriya
D
Chantasingh
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. jajen@biotec.or.th.
Janet Jennifer
JJ
Luangsa-ard
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. lily@biotec.or.th.
Lily
L
Eurwilaichitr
D000818:Animals; D016681:Genome, Fungal / Q000235:genetics*; D058507:Host Specificity / Q000235:genetics*; D054884:Host-Pathogen Interactions / Q000235:genetics*; D006999:Hypocreales / Q000235:genetics; D052981:Metarhizium / Q000235:genetics / Q000502:physiology*; D010802:Phylogeny; D051381:Rats; D014774:Virulence / Q000235:genetics*