Sequence Analysis And Biological Characteristics Of Hypovirus FgHV1 From Fusarium Graminearum

Fungal viruses (mycoviruses) occur in all four phyla of the true fungi. Fusarium graminearum isolates from China were screened for dsRNA mycoviruses. A double-stranded (ds) RNA element, sized at approximately 13 kilobase pairs, was purified from a field isolate, HN10, of Fusarium graminearum. Sequence alignments indicated the dsRNA represent the genome of a nove mycovirus. Phylogenetic analysis showed that the virus existed in strain HN10 belongs to the hypoviridae and was designated FgHV1/HN10. We also exploe the influence of the virus on biological properties of host strain HN10. This paper will lay foundation for the study of mycoviruses of Fusarium. spp isolated from China and provide resources for the clarification of phylogenetic relationships among viruses in the family hypoviridae.1. Totally,1,429 strains of Fusarium.spp were isolated from infected wheat head growen on the major wheat producing proviences. Through CF-11 dsRNA purification, we detected 16(23%) out of 70 isolates collected. The dsRNA fragment size ranged from 1700bp to 13000bp. And several fragments could be detected from some strains. A dsRNA fragment sized at more than 10kb was purified from strain HN10. Result of blast for the sequence of EF-1 suggest that strain HN10 was Fusarium graminearum.2. Through sequence assembling of clones got with random primers, sequence specific primers and RACE, a stand of 13,023bp tailed with polyA was obtained.3. The coding strand of the dsRNA was 13023 nucleotides (nt) long (excluding the 3’ poly-A tail) and was predicted to contain two discontiguous open reading frames (ORF A and ORF B). The 5’ proximal ORF A of 531 nt encoded a protein of 176 amino acids (aa), and a BLAST search showed it to be similar to the putative papain-like protease domains encoded by Valsa ceratosperma hypovirus 1 (35% identity) and Cryphonectria hypovirus 4 (CHV4) (31% identity). The 3’proximal ORF B of 11118 nt encoded a large polyprotein with three conserved domains, including papain-like protease, RNA-dependent RNA polymerase and RNA helicase domains. The polyprotein shared significant aa identities with CHV1 (32%) and CHV2 (32%). Both the genome organization and phylogenetic analysis suggested that the characterized RNA represented a novel hypovirus, designated "Fusarium graminearum hypoyirus 1 (FgHV1)", which was closely related to CHV1 and CHV2 in the Hypoviridae family.4. FgHV1/HN10 infection had minor reductions in mycelial growth rate and conidiation production while the virus had no effects on fungal phenotypes including morphology, sexual reproduction, virulence or toxin production.