The Expanding Roles of Mycoviruses in Regulating Fungal and Ecological Systems

Abstract

Mycoviruses, or viruses that infect and replicate within fungal and fungus‐like organisms (oomycetes) hosts, have traditionally been considered latent and marginal players. Most mycoviruses remain within fungal cells and usually lack a classical extracellular stage, which has contributed to the underestimation of their roles in nature and biotic interactions. However, breakthroughs in high‐throughput sequencing and meta‐transcriptomics have revolutionized this conventional view of mycoviruses. Current evidence suggests that mycoviruses are ubiquitous and dynamic components of fungal viromes, occurring across major fungal lineages and fungus‐like oomycetes. Recent studies on mycoviruses suggest that these viruses are genomically diverse and possess significant potential to revolutionize the physiology, metabolism, growth, and pathogenicity of their hosts. Such effects of mycoviruses on their hosts often result in hypovirulence, toxin reduction, and even lifestyle shifts in pathogenic fungi toward endophytism. Such effects of mycoviruses on their hosts directly impact plant health and biotic interactions. Concurrently, significant taxonomic changes of mycoviruses, mainly based on genomics and phylogenetics, suggest that mycovirus evolution is not strictly linear and is influenced by mechanisms such as genome reduction, recombination, genome fragmentation, and horizontal gene transfer. This review presents current evidence on mycovirus diversity, taxonomy, evolutionary origins, and interactions with their hosts, showing that mycoviruses, though latent, are major players in controlling fungal hosts. Furthermore, their significant potential to sustainably control plant diseases makes mycoviruses among the most promising biotechnological tools for future agricultural applications.