The Genome Sequence And Construction Of Full-Length Infectious CDNA Clone Of Hypovirus CHV1-EP721

Hypoviruses are a group of dsRNA viruses associated with the reduced virulence (hypovirulence) of the chestnut blight fungus Cryphonectria parasitica. The field strain EP721 of C. parasitica had been found to be infected by a hypovirus termed CHV1-EP721. EP721 shows typical hypovirulence-associated phenotype, reduced pigmentation, reduced asexual sporulation and female infertility. Comparison with other known hypoviruses, the accumulation of CHV1-EP721 in the cells of fungus is significantly lower. By construction and sequencing of a cDNA library of the virus, the whole genome sequence of CHV1-EP721 was determined. The virus showed extensive identities with the other two known hypovirus: CHV1-Euro7 and CHV1-EP713, with an average of 99% and 90% identities at nuceotide level and 99% and 92% identities at amino acids level respectively.The full-lenghth cDNA clone of the virus was constructed by accurately joining viral cDNA fragments according to the whole genome sequence with aid of restriction enzymes. By transfection, CHV1-EP721 was successfully introduced into virus-free fungal host strains EP721(-), EP155 and Euro7(-). All of the transfected strains showed similar phenotype to EP721 and the CHV1-EP721 dsRNA accumulation in different hosts were lower than those tranfected by CHV1-Euro7 and CHV1-EP713, conforming the low level of viral accumulation was the property of the virus. The availability of infectious cDNA clone of CHV1-EP721 makes it possible to dissect the molecular basis of a viral genome that controls the viral accumulation in the host and to understand other aspects of interaction between host and virus.