Complete genome sequence of a novel alternavirus infecting the fungus Ilyonectria crassa

Area of Science:

• Mycology
• Virology
• Plant Pathology

Background:

• Ash dieback, a disease affecting *Fraxinus excelsior*, is caused by the fungus *Hymenoscyphus fraxineus*.
• Fungal viruses (mycoviruses) can influence host pathogenicity and fitness.
• The diversity of mycoviruses in plant-pathogenic fungi remains largely unexplored.

Purpose of the Study:

• To identify and characterize novel mycoviruses associated with *Ilyonectria crassa*.
• To determine the genomic features and phylogenetic relationships of a newly discovered dsRNA mycovirus.
• To investigate the potential impact of this mycovirus on its fungal host.

Main Methods:

• Isolation and culturing of *Ilyonectria crassa* from infected ash trees.
• Next-generation sequencing to identify viral dsRNA segments.
• Bioinformatic analysis for genome assembly, annotation, and phylogenetic reconstruction.

Main Results:

• Discovery and characterization of Ilyonectria crassa alternavirus 1 (IcAV1), a novel tripartite dsRNA mycovirus.
• IcAV1 possesses conserved 5' UTRs and polyadenylated 3' UTRs, with ORFs encoding RdRP and capsid proteins.
• Phylogenetic analysis places IcAV1 within the proposed family "Alternaviridae", closely related to other alternaviruses.

Conclusions:

• IcAV1 is the first reported mycovirus infecting *Ilyonectria crassa*.
• The virus genome organization and phylogenetic placement support its classification as a new member of the "Alternaviridae" family.
• Further research is needed to elucidate the function of the segment 2-encoded protein and the ecological role of IcAV1.