Transcriptomic Insight Into Pathogenicity-associated Factors Of An Obligate Aphid-pathogenic Fungus Conidiobolus Obscurus (Entomophthoromycotina)

Entomophthoralean fungi can cause pest epizootics in nature,holding characteristics of high virulence and host specificity.Conidiobolus obscurus(Entomophthoromycotina)is an important fungus to control aphid pests worldwide.Its hosts include agricultural and forestry pests such as green peach aphid and bamboo aphids.In the present study,we unraveled pathogenicity-associated factors of the entomopathogen C.obscurus based on de novo transcriptomic analysis.The main results are list as following.1.We obtained a total of 1.4×108reads from the transcriptomes,and assembled 76643 unigenes,including 17231 from C.obscurus.A wide variety of pathogenicity-associated genes were detected among the assembled fungal unigenes,such as subtilisin-like proteolytic enzymes(Pr1s),trypsin-like proteases,metalloproteases,carboxypeptidases and endochitinases.Compared to fungal culture,the expression of 1110 unigenes changed significantly in mycotized cadavers,including 985 upregulated and 125 downregulated unigenes.Among the top upregulated transcripts in the mycotized cadavers are various protein groups,including proteases,peptidases,and other hydrolases.It indicated that these unigenes involve in infection processing of utilizing host tissues and breeching the host integument.The Pr1-like and insecticidal crystal protein-coding Cyt-like unigenes show sequence uniqueness among homologs of the reported fungal origins through the phylogenetic trees.2.The expression levels of pathogenicity-related genes on conidia,fungual liquid or solid cultures,and mycotized cadavers were assessed by fluorescence quantitative PCR.There are significant differences of Pr1 and Pr2 under different growth conditions,highly expressed in mycotized cadavers,consistent with the results of transcriptomics analysis.In addition,the expression levels of Cyt-like gene under different culture conditions was evaluated as well.The results showed that the optimal culture temperature of Cyt-like expression was 20 ?,the 4 % glucose concentration,and 3 days of culture.Moreover,the expression of this gene gradually decreased with the increase of transfer generations.For the first time,this study comprehensively analyzed the pathogenicity-associated factors with C.obscurus.It provides necessary information for unraveling host-pathogen interaction and may helpthe development of practical application.