The complete genome sequence of a novel Fusarium graminearum RNA virus in a new proposed family within the order Tymovirales

The complete nucleotide sequence of Fusarium graminearum deltaflexivirus 1 (FgDFV1), a novel positive single-stranded (+ss) RNA mycovirus, was sequenced and analyzed. The complete genome of FgDFV1/BJ59 was shown to be 8246 nucleotides (nt) long excluding the poly(A) tail. FgDFV1/BJ59 was predicted to contain a large open reading frame (ORF 1) and four smaller ORFs (2-5). ORF1 encodes a putative replication-associated polyprotein (RP) of 2042 amino acids (aa) and contains three conserved domains, viral RNA methyltransferase (Mtr), viral RNA helicase (Hel) and RNA-dependent RNA polymerase (RdRp). ORFs 2-5 encode four putative small hypothetical proteins (12-18 kDa) with unknown biological functions. Phylogenetic analysis based on RP sequences indicated that FgDFV1 is phylogenetically related to soybean leaf-associated mycoflexivirus 1 (SlaMyfV1) and Sclerotinia sclerotiorum deltaflexivirus 1 (SsDFV1), which form a well-supported and independent group belonging to a newly proposed family Deltaflexiviridae within the order Tymovirales. However, FgDFV1 is markedly different from SsDFV1 and SlaMyfV1 in genome organization and nucleotide sequence. FgDFV1 may represent an additional species in the new genus Deltaflexivirus or possibly a new genus in the proposed family Deltaflexiviridae.