Molecular characterization of a novel fusagravirus in the phytopathogenic fungus Streptobotrys caulophylli.

Streptobotrys caulophylli is a pathogenic fungus that causes leaf and stem blight in many plants. We report a novel fusagravirus identified in S. caulophylli strain STB-2, provisionally named "Streptobotrys caulophylli fusagravirus 1" (ScFV1). The full-length genome of ScFV1 is 9270 nucleotides (nt) long and putatively possesses two large open reading frames (ORF1 and ORF2), which are separated by an intergenic region of 955 nt. A conserved domain search revealed that ORF2 (1051 aa) encodes a putative RNA-dependent RNA polymerase (RdRp), whereas ORF1 (1404 aa) encodes a protein of unknown function. Homology searches and phylogenetic analysis of the putative RdRp suggest that ScFV1 is a new member of the proposed family "Fusagraviridae". This is the first report of a mycovirus infecting the fungus S. caulophylli.