Host-to-Pathogen Gene Transfer Facilitated Infection of Insects by a Pathogenic Fungus

Metarhizium robertsii is a plant root colonizing fungus that is also an insect pathogen. its entomopathogenicity is a characteristic that was acquired during evolution from a plant endophyte ancestor. this transition provides a novel perspective on how new functional mechanisms important for host switching and virulence have evolved. from a random t-dna insertion library,we obtained a pathogenicity defective mutant that resulted from the disruption of a sterol carrier gene (mr-npc2a). phylogenetic analysis revealed that metarhizium acquired mr-npc2a from an insect by horizontal gene transfer (hgt). mr-npc2a binds to cholesterol,an animal sterol,rather than the fungal sterol ergosterol,indicating it retains the specificity of insect npc2 proteins. mr-npc2a is an intracellular protein and is exclusively expressed in the hemolymph of living insects. the disruption of mr-npc2a reduced the amount of sterol in cell membranes of the yeast-like hyphal bodies that facilitate dispersal in the host body. these were consequently more susceptible to insect immune responses than the wild type. transgenic expression of mr-npc2a increased the virulence of beauveria bassiana,an endophytic insect-pathogenic fungus that lacks a mr-npc2a homolog. © 2014 zhao et al.