The Replicase Gene of Avian Coronavirus Infectious Bronchitis Virus Is a Determinant of Pathogenicity

Abstract

We have previously demonstrated that the replacement of the S gene from an avirulent strain (Beaudette) of infectious bronchitis virus (IBV) with an S gene from a virulent strain (M41) resulted in a recombinant virus (BeauR-M41(S)) with the in vitro cell tropism of the virulent virus but that was still avirulent. In order to investigate whether any of the other structural or accessory genes played a role in pathogenicity we have now replaced these from the Beaudette strain with those from M41. The recombinant IBV was in effect a chimaeric virus with the replicase gene derived from Beaudette and the rest of the genome from M41. This demonstrated that it is possible to exchange a large region of the IBV genome, approximately 8.4 kb, using our transient dominant selection method. Recovery of a viable recombinant IBV also demonstrated that it is possible to interchange a complete replicase gene as we had in effect replaced the M41 replicase gene with the Beaudette derived gene. Analysis of the chimaeric virus showed that it was avirulent indicating that none of the structural or accessory genes derived from a virulent isolate of IBV were able to restore virulence and that therefore, the loss of virulence associated with the Beaudette strain resides in the replicase gene.

The genotyping of Infectious bronchitis virus in Taiwan by a multiplex amplification refractory mutation system reverse transcription polymerase chain reaction

“…2,27 The S protein is located at the exterior surface of the envelope of IBV and is cleaved into S1 and S2 subunits during maturation. 1 Because the epitopes eliciting neutralizing antibodies are widely distributed within the S protein sequence, as little as 2% variation in amino acid sequence, either by mutation or recombination, can lead to a new IBV serotype. 3,16 Importantly, 2 exclusively Taiwan groups of IBV, Taiwan group I (TW-I) and Taiwan group II (TW-II), have been shown to co-circulate with the vaccine strains in the field.…”

Evaluation of a novel strain of infectious bronchitis virus emerged as a result of spike gene recombination between two highly diverged parent strains

“…As the S1 gene encodes the section of the spike glycoprotein that is responsible for binding to the host cell receptor (Cavanagh et al, 1986), changes to the S1 gene can have significant implications for virulence, tissue tropism and persistence in a host (Wentworth & Holmes, 2007). However, one should also note that investigation into the non-structural genes located in the RdRP region upstream of the S1 gene has concluded that genes in this region also contribute to strain virulence (Armesto et al, 2009). Sequence analysis of the N1/08 RdRP genes and comparative evaluation of the pathogenicity of N1/08 with that of the subgroup 2 and 3 viruses were not possible in this investigation, and would be required to confirm any conclusions as to the implications that these sequence variations have on the virulence of N1/08.…”

Genomic Characteristics and Changes of Avian Infectious Bronchitis Virus Strain CK/CH/LDL/97I after Serial Passages in Chicken Embryos

“…However, such conclusions should be drawn with caution, as the results of this and other studies found no identical substitutions, insertions, or deletions in S proteins between different pathogenic IBV strains and their embryo-passaged, attenuated derivatives, even though the attenuated IBV strains showed distinctly different biological features, including lack of pathogenicity to 1-day-old SPF chicks compared to the pathogenic parental strains [26,30,31] . Some findings suggested that the replicase gene, rather than the S1 or S gene, may be responsible for viral pathogenicity [32,33] .…”

“…The ectodomain region [33] and two heptad repeat regions [34] of subunit S2 are involved in oligomerization of the S protein and required for entry into susceptible cells [35][36][37] . Changes in the S2 gene may affect viral entry [32] . In this study, multiple changes in the S2 gene occurred during passage of CK/CH/LDL/97I in embryonated eggs, which may have had an effect on viral entry into chicken host cells in vivo, indirectly decreasing the replication capacity.…”