In vivo transcriptome analysis of the entomopathogenic fungus Beauveria bassiana strain GHA during infection against the beneficial predator tobacco leaf bug, Nesidiocoris tenuis (Hemiptera: Miridae)
摘要
The entomopathogenic fungus Beauveria bassiana strain GHA, the active ingredient of a commercial mycoinsecticide, is used to control many insect pests. However, this strain also infects and causes high mortality in the beneficial predatory insect Nesidiocoris tenuis (Reuter) (Hemiptera: Miridae, tobacco leaf bug), which is widely used as a biological control agent in agriculture to manage various small insect pests. As a part of our efforts to understand the pathogenicity mechanism to explore new technologies that address this weakness, we investigated whether candidate virulence genes could be selected by comparing the in vivo transcriptome of strain GHA on tobacco leaf bugs across different infection stages. First, microscopic observation and quantitative genomic PCR during the infection revealed that penetration of the cuticle began around 36 h postinoculation, and the mycelium spread within the hemocoel by 72 h. RNA-Seq analyses conducted on inoculated hosts at 36 h (cuticle penetration stage) and 72 h (hemocoel growth stage) postinoculation identified 83 and 99 genes, respectively, that were expressed at relatively higher levels at these stages. Both gene sets contained homologs of previously identified virulence genes with functions corresponding to their respective infection stages, such as adhesion, appressorium formation, cuticle degradation, and immunosuppression. Gene enrichment analysis also supported the enrichment of extracellular and hydrolase terms potentially involved in cuticle degradation in the transcriptome at 36 h postinoculation. These findings indicate the potential efficacy of comparative in vivo transcriptomic analysis between infection stages for selecting the virulence genes of entomopathogenic fungi against tobacco leaf bugs.