A cDNA-based reverse genetics system for feline calicivirus identifies the 3′ untranslated region as an essential element for viral replication

Virulent systemic feline calicivirus (VS-FCV) is a newly emerging FCV variant that is associated with a severe acute multisystem disease in cats that is characterized by jaundice, oedema, and high mortality (approximately 70%). VS-FCV has spread throughout the world, but there are no effective vaccines or therapeutic options to combat infection. VS-FCV may therefore pose a serious threat to the health of felines. The genomic characteristics and functions of VS-FCV are still poorly understood, and the reason for its increased pathogenicity is unknown. Reverse genetics systems are powerful tools for studying the molecular biology of RNA viruses, but a reverse genetics system for VS-FCV has not yet been reported. In this study, we developed a plasmid-based reverse genetics system for VS-FCV in which infectious progeny virus is produced in plasmid-transfected CRFK cells. Using this system, we found that the 3' untranslated region (UTR) and poly(A) tail are important for maintaining the infection and replication capacity of VS-FCV and that shortening of the poly(A) tail to less than 28 bases eliminated the ability to rescue infectious progeny virus. Whether these observations are unique to VS-FCV or represent more-general features of FCV remains to be determined. In conclusion, we successfully established a rapid and efficient VS-FCV reverse genetics system, which provides a good platform for future research on the gene functions and pathogenesis of VS-FCV. The effects of the deletion of 3' UTR and poly(A) tail on VS-FCV infectivity and replication also provided new information about the pathogenesis of VS-FCV.