key: cord-272437-gvzfl8c3
authors: Zhao, Jing; Zhang, Keran; Cheng, Jinlong; Jia, Wenfeng; Zhao, Ye; Zhang, Guozhong
title: Replicase 1a gene plays a critical role in pathogenesis of avian coronavirus infectious bronchitis virus
date: 2020-08-20
journal: Virology
DOI: 10.1016/j.virol.2020.08.009
sha: 
doc_id: 272437
cord_uid: gvzfl8c3

Avian coronavirus infectious bronchitis virus (IBV) is an important pathogen threatening poultry production worldwide. Here, two recombinant IBVs (rYN-1a-aYN and rYN-1b-aYN) were generated in which ORF1a or ORF1b of the virulent YN genome were replaced by the corresponding regions from the attenuated strain aYN. The pathogenicity and virulence of rIBVs were evaluated in ovo and in vivo. The results revealed that mutations in the ORF1a gene during passage in embryonated eggs caused the decreased pathogenicity of virulent IBV YN strain, proven by determination of virus replication in ECEs and CEK cells, the observation of clinical signs, gross lesions, microscopic lesions, tracheal ciliary activity and virus distribution in chickens following exposure to rIBVs. However, mutations in ORF1b had no obvious effect on virus replication in both ECEs and CEK cells, or pathogenicity in chickens. Our findings demonstrate that the replicase 1a gene of avian coronavirus IBV is a determinant of pathogenicity.

. those of the rYN group at 5 and 7 dpi (p < 0.01 or 0.001) (Fig. 4B ). In the lungs, the 264 virus copy numbers in the rYN-1a-aYN infected group were also significantly lower 265 than those of the rYN group at 7 and 10 dpi (p < 0.01 or 0.001) (Fig. 4C) . The

numbers of viral RNA copies in the kidneys of the rYN-1a-aYN infected group were 267 lower than in the rYN group at 10 dpi (p < 0.001) (Fig. 4D ). There were no ORF1a limited viral replication in chicken tissues.

IBV is a highly infectious pathogen in domestic fowl that replicates mainly in the 

This may indicate that avirulent strain Beaudette was not the ideal background in 296 which to study the role of IBV-specific mutations in pathogenicity. We suspect that 297 mutations in the replicase gene may play an important role in attenuation of IBV.

In this study, we used an IBV reverse genetics system based on virulent strain Fig. 2. Growth characteristics of IBV rYN, rYN-1a-aYN or rYN-1b-aYN, and   466 clinical scores and survival rates of chickens inoculated with these IBV strains. IBV rYN, rYN-1a-aYN and rYN-1b-aYN strains. 

Statistical significance was considered as follows: highly significant at p < 0.01 (**) 482 and extremely significant at p < 0.001 (***). 

is critical for viral virulence

Infectious bronchitis virus variants: a 425 review of the history, current situation and control measures

Chapter three -The nonstructural proteins directing 427

coronavirus RNA synthesis and processing

Recombinant live attenuated avian coronavirus 431 vaccines with deletions in the accessory genes 3ab and/or 5ab protect against infectious 432 bronchitis in chickens

Coronavirus pathogenesis

Attenuation, safety, and efficacy of a QX-like infectious bronchitis virus serotype 445 vaccine

Porcine deltacoronavirus: Overview of infection dynamics, diagnostic methods, 447 prevalence and genetic evolution

attenuated Chinese QX-like infectious bronchitis virus strain as a candidate vaccine

Successful establishment of a reverse 452 genetic system for QX-type infectious bronchitis virus and technical improvement of the 453 rescue procedure

S gene and 5a accessory gene 455 are responsible for the attenuation of virulent infectious bronchitis coronavirus

Coronavirus replicative proteins

Virus-encoded proteinases and proteolytic 460 processing in the Nidovirales