Transcriptomic insight into pathogenicity-associated factors of Conidiobolus obscurus, an obligate aphid-pathogenic fungus belonging to Entomopthoromycota.

BACKGROUND: Conidiobolus obscurus is a widespread fungal entomopathogen with aphid biocontrol potential. This study focused on a de novo transcriptomic analysis of C. obscurus.

RESULTS: A number of pathogenicity-associated factors were annotated for the first time from the assembled 17 231 fungal unigenes, including those encoding subtilisin-like proteolytic enzymes (Pr1s), trypsin-like proteases, metalloproteases, carboxypeptidases and endochitinases. Many of these genes were transcriptionally up-regulated by at least twofold in mycotized cadavers compared with the in vitro fungal cultures. The resultant transcriptomic database was validated by the transcript levels of three selected pathogenicity-related genes quantified from different in vivo and in vitro material in real-time quantitative polymerase chain reaction (PCR). The involvement of multiple Pr1 proteases in the first stage of fungal infection was also suggested. Interestingly, a unique cytolytic (Cyt)-like δ-endotoxin gene was highly expressed in both mycotized cadavers and fungal cultures, and was more or less distinct from its homologues in bacteria and other fungi.

CONCLUSION: Our findings provide the first global insight into various pathogenicity-related genes in this obligate aphid pathogen and may help to develop novel biocontrol strategy against aphid pests. © 2018 Society of Chemical Industry.