| Mycoviruses can exist and stably replicate in fungal cells.In recent years,a large number of new mycoviruses with their genome sequences have been reported,which mainly belong to 14 families and a portion of virus are unclassified yet.The mycoviruses genome nucleic acid types include dsRNA,(+)ssRNA,(-)ssRNA and ssDNA.Although most of mycoviruses have no significant effect on the host,many hypovirulence-associated mycoviruses in a variety of plant pathogenic have been discovered nowadays,and provide a rich resource for biological control of fungal diseases.The binucleate fungal species Rhizoctonia cerealis Van der Hoeven belongs to the Rhizoctonia AG-DI anastomosis group and is the dominant pathogen of wheat sharp eyespot in China.dsRNA exists with rich diversity in some strains of R.cerealis,but studies of mycoviruses in Rhizoctonia especially in the binucleate R.cerealis are little.High-throughput sequencing and analysis of dsRNA extracted from the weak virulent strains of R.cerealis showed mycovirus in R.cerealis include a variety of mycoviruses sequences.Exploring the correspond relationship between these sequences and hypovirulence of the strains can provide valuable clues to find potenial biocontrol viruses.A candidate novel mitovirus was found in isolate R1084 of R.cerealis.The full genome sequence of the virus was obtained and characterized.The complete cDNA sequence is 3149 nucleotides long with 59.7%A+U content.Using either the fungal mitochondrial or the universal genetic code,a single large open reading frame was predicted.It encodes a protein of 812 amino acids with an RNA-dependent RNA polymerase(RdRp)conserved domain conserved in the mitovirus RdRp superfamily.The RdRp domain is only 50%similar to the corresponding domain of Sclerotinia sclerotiorum mitovirus 11,and is therefore proposed as a novel mitovirus designated as Rhizoctonia cerealis mitovirus 1-R1084(RcMV1-R1084).The distinct codon usage of RcMV1-R1084 hints that this virus is potentially able to replicate not only in mitochondria but also in the cytoplasm.This is the first report of a full-length genomic sequence of a putative mitovirus in R.cerealis.In this study,we found part genome sequences of two viruses from the hypovirulence R.cereal is strain R10125 and deduced that they may belong to the Mitovirus and Hypovirus respectively.Accordingly,we proposed the name Rhizoctonia cerealis Mitovirus 2/R10125(RcMV2/R10125)and Rhizoctonia cerealis Hypovirus 1/R10125(RcHV1/R10125).For RcMV2/R10125,a intact single large open reading frame was predicted.It encodes a protein of 902 amino acids with an RNA-dependent RNA polymerase(RdRp)conserved domain conserved in the mitovirus RdRp superfamily.There is a large sequence difference between RcMV2/R10125 and RcMV1-R1084.Compared with other hypoviruses,It was estimated RcHV1/R10125 may have longer sequence unknown.We speculated that there may be more than one case of mycovirus infecting the same strain of the R10125 and R1084,which may contain hypovirulence-associated mycovirus.We selected the weak virulent R.cerealis strains R1084 and R10125,with the purpose to explore the mechanisms of their hyporivulence.We found that the colony and mycelial morphology,mycelial growth rate of the offspring obtained from hyphal tip of R10125 were significantly restored,and the pathogenicity to wheat seedlings was enhanced.Colony morphology of the isolates from R0959 after confront cultured with R1084 or R10125 was seriously degraded with irregular clonies,slow growth rate,abnormal hyphal in a zigzag style and reduced virulence.But the traits of isolates from R0301 did not show obvious changes in colony morphology,growth rate and virulence after confront cultured with R1084 or R10125.This study suggested that R.cerealis strains R10125 may contain hyporivulence-associated factors that need to be further clarified. |
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