Lifestyle plasticity and the shared hypocrealean toolkit across <i>Fusarium</i> , <i>Metarhizium</i> , and <i>Trichoderma</i>

SUMMARY Fungi in the genera Fusarium , Metarhizium , and Trichoderma (FMT) are traditionally defined by their roles as plant pathogens, insect pathogens, and mycoparasites, respectively. However, these classifications obscure both their shared hypocrealean ancestry and the remarkable ecological plasticity that characterizes all three genera. Across these lineages, plant endophytism appears to represent the predominant ecological state, with frequent transitions among saprotrophy, symbiosis, pathogenicity, and antagonism. Comparative genomics reveals that FMT fungi possess two-speed genomes comprising conserved core chromosomes and dynamic accessory regions enriched in host-interaction and secondary metabolism genes. These architectures support a shared hypocrealean genomic toolkit that has been differentially modified across lineages. In Fusarium , transitions along the mutualism-to-pathogenicity continuum appear to be driven primarily by regulatory plasticity rather than by major changes in gene content. By contrast, Metarhizium and Trichoderma expanded from ancestral pathogenic states toward broader plant associations through horizontal gene transfer, gene duplication, and diversification of host-recognition, signaling, and metabolite-production pathways. Reproductive strategies similarly reflect ecological divergence. Generalist lineages are predominantly clonal, whereas specialists more frequently retain sexual reproduction, facilitating adaptation to predictable hosts and environments. Ecologically, FMT fungi occupy overlapping but distinct niches: Trichoderma dominates stable environments through mycoparasitism and competitive exclusion; Fusarium thrives in disturbed habitats through rapid colonization of stressed plants; and Metarhizium bridges soil, plant, and insect environments through combined root association and insect pathogenicity. Collectively, FMT fungi illustrate how divergent ecological strategies can emerge through differential modification and regulatory deployment of a shared hypocrealean genomic toolkit.