Evidence for a mouse origin of the SARS-CoV-2 Omicron variant

The rapid accumulation of mutations in the SARS-CoV-2 Omicron variant that enabled its outbreak raises questions as to whether its proximal origin occurred in humans or another mammalian host. Here, we identified 45 point mutations that Omicron acquired since divergence from the B.1.1 lineage. We found that the Omicron spike protein sequence was subjected to stronger positive selection than that of any reported SARS-CoV-2 variants known to evolve persistently in human hosts, suggesting the possibility of host-jumping. The molecular spectrum (i.e., the relative frequency of the twelve types of base substitutions) of mutations acquired by the progenitor of Omicron was significantly different from the spectrum for viruses that evolved in human patients, but was highly consistent with spectra associated with evolution in a mouse cellular environment. Furthermore, mutations in the Omicron spike protein significantly overlapped with SARS-CoV-2 mutations known to promote adaptation to mouse hosts, particularly through enhanced spike protein binding affinity for the mouse cell entry receptor. Collectively, our results suggest that the progenitor of Omicron jumped from humans to mice, rapidly accumulated mutations conducive to infecting that host, then jumped back into humans, indicating an inter-species evolutionary trajectory for the Omicron outbreak.

SARS-CoV-2 originated from SARS-CoV-1-related Bat-CoVs through Pan-CoVs rather than from SARS-CoV-2-related Bat-CoVs

The emergence of the novel SARS-CoV-2 in 2019 sparked a dispute concerning its origin. Here, we report that the SARS-CoV-2 originated through pangolin-coronavirus (Pan-CoVs) from the SARS-CoV-related-bat-coronaviruses (SARS-CoV-1-rB-CoVs) rather than from SARS-CoV-2-related-bat-coronaviruses (SARS-CoV-2-rB-CoVs), in contrast to the previous thought. Further, our analyses strongly suggest that the Pan-CoVs evolved from the SARS-CoV-1-rB-CoVs without recombination. Further, our results suggest that the SARS-CoV-1-rB-CoVs’ perhaps jumped into the pangolin, which forced the viruses to mutate and adapt to the new host, and resulted in the origin of Pan-CoVs. Surprisingly, the Pan-CoVs formed an evolutionary intermediate between SARS-CoV-2 and SARS-CoV-2-rB-CoVs at the spike gene. Our findings also suggest that the Pan-CoV/GX and Pan-CoV/Guangdong lineages recombined to form the SARS-CoV-2 spike gene. We also found evidence that the SARS-CoV-2-rB-CoVs spike gene evolved via recombination between Pan-CoV/Guangdong and SARS-CoV-1-rB-CoVs. Overall, our findings suggest that the SARS-CoV-2 emerged from SARS-CoV-1-rB-CoVs through host jumping.

Positive selection and intrinsic disorder are associated with multifunctional C4(AC4) proteins and geminivirus diversification

Viruses within the Geminiviridae family cause extensive agricultural losses. Members of four genera of geminiviruses contain a C4 gene (AC4 in geminiviruses with bipartite genomes). C4(AC4) genes are entirely overprinted on the C1(AC1) genes, which encode the replication-associated proteins. The C4(AC4) proteins exhibit diverse functions that may be important for geminivirus diversification. In this study, the influence of natural selection on the evolutionary diversity of 211 C4(AC4) genes relative to the C1(AC1) sequences they overlap was determined from isolates of the Begomovirus and Curtovirus genera. The ratio of nonsynonymous (dN) to synonymous (dS) nucleotide substitutions indicated that C4(AC4) genes are under positive selection, while the overlapped C1(AC1) sequences are under purifying selection. Ninety-one of 200 Begomovirus C4(AC4) genes encode elongated proteins with the extended regions being under neutral selection. C4(AC4) genes from begomoviruses isolated from tomato from native versus exotic regions were under similar levels of positive selection. Analysis of protein structure suggests that C4(AC4) proteins are entirely intrinsically disordered. Our data suggest that non-synonymous mutations and mutations that increase the length of C4(AC4) drive protein diversity that is intrinsically disordered, which could explain C4/AC4 functional variation and contribute to both geminivirus diversification and host jumping.

Virus Host Jumping Can Be Boosted by Adaptation to a Bridge Plant Species

Understanding biological mechanisms that regulate emergence of viral diseases, in particular those events engaging cross-species pathogens spillover, is becoming increasingly important in virology. Species barrier jumping has been extensively studied in animal viruses, and the critical role of a suitable intermediate host in animal viruses-generated human pandemics is highly topical. However, studies on host jumping involving plant viruses have been focused on shifting intra-species, leaving aside the putative role of “bridge hosts” in facilitating interspecies crossing. Here, we take advantage of several VPg mutants, derived from a chimeric construct of the potyvirus Plum pox virus (PPV), analyzing its differential behaviour in three herbaceous species. Our results showed that two VPg mutations in a Nicotiana clevelandii-adapted virus, emerged during adaptation to the bridge-host Arabidopsis thaliana, drastically prompted partial adaptation to Chenopodium foetidum. Although both changes are expected to facilitate productive interactions with eIF(iso)4E, polymorphims detected in PPV VPg and the three eIF(iso)4E studied, extrapolated to a recent VPg:eIF4E structural model, suggested that two adaptation ways can be operating. Remarkably, we found that VPg mutations driving host-range expansion in two non-related species, not only are not associated with cost trade-off constraints in the original host, but also improve fitness on it.

Virus Host Jumping Can Be Boosted by Adaptation to a Bridge Plant Species

Understanding biological mechanisms that regulate emergence of viral diseases, in particular those events engaging cross-species pathogens spillover, are becoming increasingly important in Virology. Species barrier jumping has been extensively studied in animal viruses, and the critical role of a suitable intermediate host in animal viruses-generated human pandemics is highly topical. However, studies on host jumping involving plant viruses have been focused on shifting intra-species, leaving aside the putative role of “bridge hosts” in facilitating interspecies crossing. Here, we take advantage of several VPg mutants, derived from a chimeric construct of the potyvirus Plum pox virus (PPV), analysing its differential behaviour in three herbaceous species. Our results showed that two VPg mutations in a Nicotiana clevelandii-adapted virus, emerged during adaptation to the bridge-host Arabidopsis thaliana, drastically prompted partial adaptation to Chenopodium foetidum. Although, both changes are expected to facilitate productive interactions with eIF(iso)4E, polymorphims detected in PPV VPg and the three eIF(iso)4E studied, extrapolated to a recent VPg:eIF4E structural model, suggested that two adaptation ways can be operating. Remarkably, we found that VPg mutations driving host-range expansion in two non-related species, not only are not associated with cost trade-off constraints in the original host, but also improve fitness on it.

Roles of host small RNAs in the evolution and host tropism of coronaviruses

Human coronaviruses (CoVs) can cause respiratory infection epidemics that sometimes expand into globally relevant pandemics. All human CoVs have sister strains isolated from animal hosts and seem to have an animal origin, yet the process of host jumping is largely unknown. RNA interference (RNAi) is an ancient mechanism in many eukaryotes to defend against viral infections through the hybridization of host endogenous small RNAs (miRNAs) with target sites in invading RNAs. Here, we developed a method to identify potential RNAi-sensitive sites in the viral genome and discovered that human-adapted coronavirus strains had deleted some of their sites targeted by miRNAs in human lungs when compared to their close zoonic relatives. We further confirmed using a phylogenetic analysis that the loss of RNAi-sensitive target sites could be a major driver of the host-jumping process, and adaptive mutations that lead to the loss-of-target might be as simple as point mutation. Up-to-date genomic data of severe acute respiratory syndrome coronavirus 2 and Middle-East respiratory syndromes-CoV strains demonstrate that the stress from host miRNA milieus sustained even after their epidemics in humans. Thus, this study illustrates a new mechanism about coronavirus to explain its host-jumping process and provides a novel avenue for pathogenesis research, epidemiological modeling, and development of drugs and vaccines against coronavirus, taking into consideration these findings.

Study of SARS-nCOV2 Indian isolates gaining insights into mutation frequencies, protein stability and prospective effect on its pathogenicity

Background: SARS-nCOV-2 is a variant of the known SARS coronavirus family. The mutations in viruses are very rapid and can play a crucial role in the evolution or devolution of the organism. This has a direct impact on “host jumping” and pathogenicity of the virus. Objective: The study aims to understand the frequency of genomic variations that have occurred in the virus affecting the Indian sub-population. The impact of variations translating to proteins and its consequences affecting protein stability and interaction were studied. Method: Phylogenetic analysis of the 140 genomes from the India region was performed, followed by SNP and Indel analysis of both CDS and non-CDS regions. This effort was followed by a prediction of mutations occurring in 8 proteins of interest and the impact on protein stability and prospective drug interactions. Results: Genomes showed variability in origin, and major branches can be mapped to the 2002 outbreak of SARS. The mutation frequency in CDS regions showed that 241 C >T, 3037 C >T, 2836 C >T, and 6312 C >A occurred in 81.5 % of genomes mapping to major genes. Corresponding mutations were mapped to protein sequences. The effect of mutations occurring in spike glycoprotein, RNA dependent RNA polymerase, nsp8, nucleocapsid and 3c protease were also mapped. Conclusion: Whilst the mutations in spike glycoprotein showcased an increase in protein stability, the residues undergoing mutations were also a part of drug binding pockets for hydroxychloroquine. Mutations occurring in other proteins of interest were leading to a decrease in protein stability. The mutations were also a part of drug binding pockets for Favipiravir, Remdesivir and Dexamethasone. The work promotes the will to analyse larger datasets to understand mutation pattern globally.