Synonymous Codon Pattern of Cowpea Mild Mottle Virus Sheds Light on Its Host Adaptation and Genome Evolution

Predicting viral host codon fitness and path shifting through tree-based learning on codon usage biases and genomic characteristics

Viral codon fitness (VCF) of the host and the VCF shifting has seldom been studied under quantitative measurements, although they could be concepts vital to understand pathogen epidemiology. This study demonstrates that the relative synonymous codon usage (RSCU) of virus genomes together with other genomic properties are predictive of virus host codon fitness through tree-based machine learning. Statistical analysis on the RSCU data matrix also revealed that the wobble position of the virus codons is critically important for the host codon fitness distinction. As the trained models can well characterise the host codon fitness of the viruses, the frequency and other details stored at the leaf nodes of these models can be reliably translated into human virus codon fitness score (HVCF score) as a readout of codon fitness of any virus infecting human. Specifically, we evaluated and compared HVCF of virus genome sequences from human sources and others and evaluated HVCF of SARS-CoV-2 genome sequences from NCBI virus database, where we found no obvious shifting trend in host codon fitness towards human-non-infectious. We also developed a bioinformatics tool to simulate codon-based virus fitness shifting using codon compositions of the viruses, and we found that Tylonycteris bat coronavirus HKU4 related viruses may have close relationship with SARS-CoV-2 in terms of human codon fitness. The finding of abundant synonymous mutations in the predicted codon fitness shifting path also provides new insights for evolution research and virus monitoring in environmental surveillance.

The Incidence and Genetic Analysis of Two Betaflexiviruses Capillovirus alphavii and Tepovirus tafpruni in Iran

Viral diseases have emerged as a serious threat to cherry trees production in Iran. To determine which virus(es) are present, three leaves from a sweet cherry tree (Qz5) with diffuse white blotch spots and deformation were subjected to high-throughput sequencing. After de novo assembly, blast analysis revealed that 12 contigs ranging from 360 to 7,433 nucleotides (nts) shared 78-96% nt identities with Capillovirus alphavii (cherry virus A, CVA) and seven contigs, ranging from 350 to 6,844 nts, shared 79-88% nt identities with Tepovirus tafpruni (prunus virus T, PrVT). During a survey, CVA, PrVT, and CVA + PrVT infections were detected in 12.6%, 5.1%, and 7.9% of 724 sour and sweet cherry samples. Phylogenetic analysis revealed that Iranian CVA was grouped into GIIIB, whereas PrVT fell into a distinct branch, which was confirmed by diversity plots. The within-population diversity was lower than the between-population diversity suggesting the contribution of a founder effect on diversification of CVA isolates. Host-specific codon adaptation analysis revealed the highest adaptation of CVA to sour cherry. This could suggest that sour cherry may be one of the closest Prunus species to wild progenitors. It raises the possibility that viruses such as CVA may have exerted evolutionary pressures influencing domestication processes. Additionally, the similarity index indicated that the common plum (Prunus domestica) may have exerted significant evolutionary pressure on CVA and PrVT. The association of CVA and PrVT was reported for the first time in the mid-Eurasian region, specifically in Iran, which represents an issue in phytosanitary certification of cherry plants.

Analysis of codon usage bias of exonuclease genes in invertebrate iridescent viruses

Invertebrate iridescent viruses (IIVs) are double-stranded DNA viruses that belong to the Iridoviridae family. IIVs result diseases that vary in severity from subclinical to lethal in invertebrate hosts. Codon usage bias (CUB) analysis is a versatile method for comprehending the genetic and evolutionary aspects of species. In this study, we analyzed the CUB in 10 invertebrate iridescent viruses exonuclease genes by calculating and comparing the nucleotide contents, effective number of codons (ENC), codon adaptation index (CAI), relative synonymous codon usage (RSCU), and others. The results revealed that IIVs exonuclease genes are rich in A/T. The ENC analysis displayed a low codon usage bias in IIVs exonuclease genes. ENC-plot, neutrality plot, and parity rule 2 plot demonstrated that besides mutational pressure, other factors like natural selection, dinucleotide content, and aromaticity also contributed to CUB. The findings could enhance our understanding of the evolution of IIVs exonuclease genes.

Investigation of CaMV-host co-evolution through synonymous codon pattern

Cauliflower mosaic virus (CaMV) has a double-stranded DNA genome and is globally distributed. The phylogeny tree of 121 CaMV isolates was categorized into two primary groups, with Iranian isolates showing the greatest genetic variations. Nucleotide A demonstrated the highest percentage (36.95%) in the CaMV genome and the dinucleotide odds ratio analysis revealed that TC dinucleotide (1.34 ≥ 1.23) and CG dinucleotide (0.63 ≤ 0.78) are overrepresented and underrepresented, respectively. Relative synonymous codon usage (RSCU) analysis confirmed codon usage bias in CaMV and its hosts. Brassica oleracea and Brassica rapa, among the susceptible hosts of CaMV, showed a codon adaptation index (CAI) value above 0.8. Additionally, relative codon deoptimization index (RCDI) results exhibited the highest degree of deoptimization in Raphanus sativus. These findings suggest that the genes of CaMV underwent codon adaptation with its hosts. Among the CaMV open reading frames (ORFs), genes that produce reverse transcriptase and virus coat proteins showed the highest CAI value of 0.83. These genes are crucial for the creation of new virion particles. The results confirm that CaMV co-evolved with its host to ensure the optimal expression of its genes in the hosts, allowing for easy infection and effective spread. To detect the force behind codon usage bias, an effective number of codons (ENC)-plot and neutrality plot were conducted. The results indicated that natural selection is the primary factor influencing CaMV codon usage bias.

Coding-Complete Sequence of Cowpea Mild Mottle Virus Isolated from Iraq

Here, we report the coding-complete sequence of Cowpea mild mottle virus (CPMMV; strain Hilla) in cowpea using total transcriptome sequencing (RNA-seq) and bioinformatics analyses. The sequence length was 8,119 bp long and has 6 open reading frames. The genome was phylogenetically close to two isolates collected from Ghana.

Evolution and host adaptability of plant RNA viruses: Research insights on compositional biases

During recent decades, many new emerging or re-emerging RNA viruses have been found in plants through the development of deep-sequencing technology and big data analysis. These findings largely changed our understanding of the origin, evolution and host range of plant RNA viruses. There is evidence that their genetic composition originates from viruses, and host populations play a key role in the evolution and host adaptability of plant RNA viruses. In this mini-review, we describe the state of our understanding of the evolution of plant RNA viruses in view of compositional biases and explore how they adapt to the host. It appears that adenine rich (A-rich) coding sequences, low CpG and UpA dinucleotide frequencies and lower codon usage patterns were found in the vast majority of plant RNA viruses. The codon usage pattern of plant RNA viruses was influenced by both natural selection and mutation pressure, and natural selection mostly from hosts was the dominant factor. The codon adaptation analyses support that plant RNA viruses probably evolved a dynamic balance between codon adaptation and deoptimization to maintain efficient replication cycles in multiple hosts with various codon usage patterns. In the future, additional combinations of computational and experimental analyses of the nucleotide composition and codon usage of plant RNA viruses should be addressed.