The evolutionary trajectory of Metarhizium robertsii as plant growth promoter and insect pathogen

Strains of Metarhizium robertsii (M. robertsii) differ in their ecological interactions as saprophytes, insect pathogens and plant symbionts. Some particularly effective plant growth promoters also have a broad host range to insects and trade insect-derived nitrogen with plants for carbohydrates. To identify the molecular underpinnings of intraspecific phenotypic differences, we compared eight sequenced M. robertsii strains that represent a range of contrasted abilities for colonization of insects and plants. We found that speed of germination on insect cuticle correlated with germination on plant roots, as well as with adaptations to the insect immune response. Additionally, using mutant fly lines, we identified Persephone-dependent processes as chiefly responsible for differential resistance toM. robertsii strains. Overall, we found no trade-offs between fungal insect-pathogenicity and endophytic ability or metabolic capacity. Instead, the most early diverged M. robertsii strains are weak as both insect pathogens and plant endophytes. Comparing M. robertsii genomes has identified a pattern of gene gain and loss contributing to both differences in fungal metabolism and ecological interactions. An overall aim of this research is to utilize genomes as predictive tools for estimating biocontrol properties and to identify the genetic and phenotypic requirements for effective biocontrol agents in the field, ultimately enhancing optimization of application strategies.