Diversity Of Viruses In Sclerotinia Sclerotiorum Of Garden Bean From America And The Study On SsAFV1

Sclerotinia sclerotiorum is an important crop pathogenic fungus with a wide host range.Sclerotinia disease caused by it causes huge economic losses to the production of rape,soybean,sunflower and other crops.Fungal viruses are viruses that parasitize fungal cells.Some of them can confer the hypovirulence to fungal hosts and have a high potential for biological control of fungal diseases.Therefore,screening and searching for hypovirulent strains of S.sclerotiorum is a crucial first step,which can enrich the diversity of fungal viruses,provide a rich resource for bio-control of S.sclerotium disease,and expand the research field of mycoviruses.In this experiment,1014 strains of S.sclerotiorum were isolated from garden beans of USA.Through morphological observation,80 strains with relatively abnormal colony morphology were selected for virome sequencing.A total of 27 viruses were detected from the virome data.The viruses belonged to positive single-stranded RNA,Mitoviridae,Alphaflexiviridae,Botourmiaviridae,Hypoviridae,Tombusviridae,Deltaflexiviridae and negative single-stranded RNA Mymonaviridae.The virus Sclerotinia sclerotiorum Alphaflexivirus 1(Ss AFV1)belonging to the Alphaflexiviridae family was identified from isolate GB862.The viral genome was 6,902 nt in length and contained a poly A structure at the 3’end.The genome of Ss AFV1 consisted of four linearly arranged open reading frames(ORFs),of which ORF1 was4,401 nt in length and encoded a replicase with a size of about 166 k Da,including the typical methyltransferase(Mrthyl transferase),helicase(RNA helicase)and RNA-dependent RNA polymerase Rd Rp,which are conserved regions in positive single-stranded RNA replicase system.The length of ORF2 was 1,107 nt in length and encoded a protein with a size of about 40 k Da,which is a unique serine-rich protein of Allexivirus genus.ORF3 was 783 nt in length and had an overlap of 207 nt with ORF3.It was presumed to encode a coat protein with a size of about 28 k Da.The length of ORF4 was 573 nt,the size of the presumed encoded protein was about 21 k Da,and the function of the protein wasunknown.According to the amino acid sequence of the replicase,the virus of family Alphaflexiviridae belongs to a new genus.The viral particles of Ss AFV1 were linear with a diameter of 10-20 nm and a length of 500-600 nm.The surface of the viral particles was smooth,bendable,and had no protruding structure.In this study,a new virus belonging to the Alphaflexiviridae family was found,which provided an important research materials for studying the ecology,phylogeny and diversity of the viruses of the Alphaflexiviridae family.