The Packaging Regions of G1-Like PB2 Gene Contribute to Improving the Survival Advantage of Genotype S H9N2 Virus in China.

Xiuli Li,Ruyi Gao,Xiufan Liu,Jing Ma,Xiaowen Liu,Shunlin Hu,Xiaoquan Wang,Zhichuang Ge,Min Gu,Jiao Hu,Daxin Peng,Sujuan Chen,Xiulong Xu,Shumiao Qiao,Xinan Jiao,Ying Zhao

doi:10.3389/fmicb.2021.655057

Abstract

The genotype S (G57) H9N2 virus, which first emerged in 2007 with the substitution of the G1-like PB2 gene for F98-like ones, has become the predominant genotype in the past 10 years. However, whether this substitution plays a role in the fitness of genotype S H9N2 viruses remains unknown. Comparison of the PB2 genes of F98-like and G1-like viruses revealed a close homology in amino acid sequences but great variations at nucleotide levels. We then determined if the packaging region, a unique sequence in each segment utilized for the assembly of the vRNA into virions, played a role in the fitness of the S genotype. The chimeric H9N2 virus with PB2 segments of the G1-like packaging regions significantly increased viral protein levels and polymerase activity. Substituting the packaging regions in the two terminals of F98-like PB2 with the sequence of G1-like further improved its competitive advantage. Substitution of the packaging regions of F98-like PB2 with those of G1-like sequences increased the infectivity of the chimeric virus in the lungs and brains of chicken at 3 days post infection (dpi) and extended the lengths of virus shedding time. Our study suggests that the packaging regions of the G1-like PB2 gene contribute to improve the survival advantage of the genotype S H9N2 virus in China.

Highlights

H9N2 viruses have evolved into multiple genotypes (A-W) since its first emergence in China in 1994
Phylogenetic analysis revealed that the PB2 genes of H9N2 AIV in China are clustered into five independent branches: that is BJ94-like, wildwaterfowl-like, F98-like, G1-like (2006) and G1-like that spread since 2007 (Supplementary Figure 1)
Nucleotide variations among PB2 nucleotides are much higher than the amino acid sequences of PB2 protein

Summary

Introduction

H9N2 viruses have evolved into multiple genotypes (A-W) since its first emergence in China in 1994. Among a few genotypes prevalent in China before 1999, the BJ94-like series is the predominant one (Gu et al, 2017; Li et al, 2017). The genotype S (G57) H9N2 viruses generated through the reassortment of F98like viruses by substituting their M and PB2 genes with those of the G1-like emerged first in 2007 and have become predominant in China since 2010s (Gu et al, 2014, 2017). The roles of G1-like M and PB2 reassortment in H7N9 and H5Nx viruses have been well characterized (Hao et al, 2019, 2020), the impact of G1-like PB2 on H9N2 virus fitness is yet to be investigated

Methods

Results

Conclusion