Host-specific patterns of virulence and gene expression profiles of the broad-host-range entomopathogenic fungus Metarhizium anisopliae

Generalist pathogens with a broad host range encounter many different host environments. Such generalist pathogens are often highly versatile and adjust their expressed phenotype to the host being infected. Species in the fungal genus Metarhizium (Hypocreales: Clavicipitaceae) occupy various ecological niches, including plant rhizosphere symbionts, soil saprophytes, and insect pathogens with applications in biological control of pests. The species M. anisopliae is highly diverse combining the capability of association with plant roots and infection of a broad range of arachnid and insect hosts, from agricultural pests to vectors of human disease. It is among the most studied and applied biological control agents worldwide. Here, we investigate the phenotypic plasticity and differential gene expression of M. anisopliae blastospores during infection of different insect hosts. First, the virulence of M. anisopliae blastospores was evaluated against Tenebrio molitor (Coleoptera: Tenebrionidae), Spodoptera frugiperda (Lepidoptera: Noctuidae), Gryllus assimilis (Orthoptera: Gryllidae), and Apis mellifera (Hymenoptera: Apidae). Second, the percentage of appressorium formation on the membranous wings of the four hosts was determined, and third, the fungal transcriptome profile during penetration on the hosts was analyzed. Our findings reveal that M. anisopliae blastospores exhibit high virulence against Tenebrio molitor, with significantly higher appressorium formation on beetle wings compared to the other three tested insects. We also document distinct gene expression patterns in M. anisopliae blastospores during insect infection of T. molitor, S. frugiperda, and A. mellifera, with notable variations observed in G. assimilis. These differences are associated with the expression of enzymes involved in the degradation of specific compounds present in each insect wing, as well as hydrophobins, destruxins, and specialized metabolites related to virulence. The study emphasizes the differences in fungal gene expression during infection of the four insect orders and highlights the virulence-related genes specific to each infective process.