Genome characterization of Botrytis virus F, a flexuous rod-shaped mycovirus resembling plant 'potex-like' viruses

This study reports the first sequence of a flexuous rod-shaped mycovirus an d also the first molecular characterization of a virus that infects the pla nt-pathogenic fungus Botrytis cinerea. The mycovirus Botrytis virus F (BVF) contains an ssRNA genome of 6827 nucleotides and a poly(A) tract at or ver y near the 3' terminus. Computer analysis of the genomic cDNA sequence of B VF revealed two potential open reading frames (ORFs) encoding proteins of 2 12 kDa (ORF1) and 32 kDa (ORF2). ORF1 showed significant sequence identity to the RNA-dependent RNA polymerase (RdRp)-containing proteins of plant 'ty mo-' and 'potex-like' viruses. However, the ORF1 protein contained an opal putative readthrough codon between the helicase and RdRp regions, a feature not seen in this position in 'tymo-' and 'potex-like' replicases sequenced to date. ORF2 shared amino acid similarity with coat proteins of plant 'po tex-like' viruses. Three untranslated regions were present in the genome, c omprising a region of 63 nucleotides preceding the initiation codon of ORF1 , a 93 nucleotide stretch between ORFs 1 and 2 and a 3'-terminal region of 70 nucleotides preceding the poly(A) tract. The nucleotide sequence of a pu tative defective RNA (D-RNA) of 829 nucleotides was also determined. The D- RNA contained one potential ORF comprising the N-terminal region of the rep licase fused in-frame to the C-terminal region of the coat protein. It is p roposed that the mycovirus BVF belongs to a new, as yet unassigned genus in the plant 'potex-like' virus group.