Naturally occurring substitution in one amino acid in VHSV phosphoprotein enhances viral virulence in flounder

Abstract

Viral hemorrhagic septicemia virus (VHSV) is a rhabdovirus that causes high mortality in cultured flounder. Naturally occurring VHSV strains vary greatly in virulence. Until now, little has been known about genetic alterations that affect the virulence of VHSV in flounder. We recently reported the full-genome sequences of 18 VHSV strains. In this study, we determined the virulence of these 18 VHSV strains in flounder and then the assessed relationships between differences in the amino acid sequences of the 18 VHSV strains and their virulence to flounder. We identified one amino acid substitution in the phosphoprotein (P) (Pro55-to-Leu substitution in the P protein; PP55L) that is specific to highly virulent strains. This PP55L substitution was maintained stably after 30 cell passages. To investigate the effects of the PP55L substitution on VHSV virulence in flounder, we generated a recombinant VHSV carrying PP55L (rVHSV-P) from rVHSV carrying P55 in the P protein (rVHSV-wild). The rVHSV-P produced high level of viral RNA in cells and showed increased growth in cultured cells and virulence in flounder compared to the rVHSV-wild. In addition, rVHSV-P significantly inhibited the induction of the IFN1 gene in both cells and fish at 6 h post-infection. An RNA-seq analysis confirmed that rVHSV-P infection blocked the induction of several IFN-related genes in virus-infected cells at 6 h post-infection compared to rVHSV-wild. Ectopic expression of PP55L protein resulted in a decrease in IFN induction and an increase in viral RNA synthesis in rVHSV-wild-infected cells. Taken together, our results are the first to identify that the P55L substitution in the P protein enhances VHSV virulence in flounder. The data from this study add to the knowledge of VHSV virulence in flounder and could benefit VHSV surveillance efforts and the generation of a VHSV vaccine.

Adaptive substitutions at two amino acids of HCPro modify its functional properties to separately increase the virulence of a potyviral chimera

“…There are reports in the literature on viral adaptation to new hosts or conditions led by changes in protein function: one recent example is the adaptation to thermal stresses of a polerovirus driven by a single amino acid substitution in its suppressor of silencing that increases its stability and its silencing suppression strength at high temperatures (Cai et al., 2023). In the case of the genus Potyvirus , examples of adaptation have been documented and associated with mutations in certain cistrons.…”

“…Ambient alterations affect host plants in their physiology (i.e., within-plant transport, intracellular conditions, molecular pathways including defence responses). Abiotic environment parameters such as, for example, ambient temperature, CO 2 partial pressures (Aguilar et al, 2015;Cai et al, 2023;Choi et al, 2017;Chung et al, 2017;del Toro et al, 2015del Toro et al, , 2018 and water deprivation (Aguilar et al, 2017;Gutiérrez-Sánchez et al, 2023) have been shown to alter the dynamics of infection. Biotic environment parameters also influence infections (i.e., exposure to, or co-infection with other viruses [Aguilar et al, 2015], or with other agents like bacteria or fungi).…”

Modifications of the nucleoprotein of viral haemorrhagic septicaemia virus showed gain of virulence in intraperitoneally infected rainbow trout

“…suggested that this cofactor is present in the P protein and could be a specific amino acid signature. Recently,Hwang et al (2021) have reported that a single substitution in the P protein of VHSV genotype IVa has enhanced virulence in olive flounder. The comparison of translated P gene of rVHSV SE 9C and DK-3592B showed only four disagreements(positions 23, 39, 41 and 210).…”