Genetic trans-complementation of L-protease fails to rescue the infectious foot-and-mouth disease virus from the Lb defective genome.

Outbreaks of the foot-and-mouth disease (FMD) have major economic impact on the global livestock industry by affecting the animal health and product safety. L-protease, a non-structural protein of FMDV, is a papain-like cysteine proteinase involved in viral protein processing as well as cleavage of host proteins for promoting the virus growth. FMDV synthesizes two forms of leader proteinase, L (Lab and Lb), where the deletion of Lab is lethal and Lb deletion is reported to be attenuated. Defective replicons have been used by trans-complementing the deleted gene to produce one time replicating virus; thus, the bio-safety procedure can be compromised in the production units. Attempts are made to rescue of ΔLbFMDV Asia1 virus by co-expressing the Lb protein carried in pcDNA plasmid. Mutant FMDV cDNA, pAsia-ΔLb, was constructed by PCR mediated mutagenesis using inverse primers. Transfection of BHK-21 cells with in-vitro transcribed RNA from the constructs failed to produce an infective mutant FMDV. Genetic trans-complementation of the Lb, which was done by co-transfecting the pcDNALb plasmid DNA along with the pAsia-ΔLb RNA in BHK-21 cells also failed to produce viable virus. Expression experiments of reporter genes and indirect immune-fluorescence confirmed the production of the viral proteins in wild type FMDV pAsia; however, it was absent in the pAsia-ΔLb indicating that the leaderless virus was unable to produce infectious progeny and infect the cells. Failure to produce virus either by Lb deleted mutant clone or by genetic complementation suggests little chance of reversion of the disabled virus with large deletions of FMDV genome.