Natural occurrence of a partitivirus in the sapstaining fungus Ceratocystis resinifera

Abstract

The bisegmented genome of a double-stranded RNA (dsRNA) virus from isolate LG115 of Ceratocystis resinifera, a sapstaining ascomycete fungus, was characterized. The larger segment (dsRNA-1) was 2305 base pairs in length, whereas the smaller one (dsRNA-2) was 2207 base pairs. The positive strand of dsRNA-1 contained an open reading frame (ORF) with the potential to encode a protein of 661 amino acids, and this ORF was closely related to coat proteins (CPs) of previously characterized fungal partitiviruses. The dsRNA-2 sequence encodes a putative protein of 663 amino acids, and this protein contains conserved motifs of RNA-dependent RNA polymerases (RDRPs) and is highly related to RDRPs of fungal partitiviruses. These results suggest that these two dsRNAs are the genome of a partitivirus. Nucleotide and amino acid comparisons revealed high similarities between this virus and a partitivirus described from Ceratocystis polonica, a closely related sapstaining fungus. Over the entire genome, the two viruses shared 82.8%–84.7% nucleotide sequence identities, and the amino acid sequence identities for CPs and RDRPs were 87.3% and 95.6%, respectively. These results suggest that the viruses in C. polonica and C. resinifera can be considered as two strains of the same partitivirus. The natural occurrence of a partitivirus in two fungal species indicates that horizontal transmission of this partitivirus may have occurred between these two fungi. Northern blot analysis indicated that this partitivirus was widespread in populations of C. resinifera.

Keywords:

• Ceratocystis resinifera
• Ceratocystis polonica
• partitivirus
• double-stranded RNA
• dsRNA
• mycovirus
• coat protein
• RNA-dependent RNA polymerase
• sapstaining
• horizontal transmission