Mitochondrial genomes of Macropsini (Hemiptera: Cicadellidae: Eurymelinae): Structural features, codon usage patterns, and phylogenetic implications.

Macropsini is a tribe of Eurymelinae in the family Cicadellidae that is widely distributed worldwide. Still, its taxonomic status has been unstable, and the classification of certain clades at the genus level has been controversial. The aim of this study is to address the patterns and processes that explain the structure and the evolution of the mitogenomes of Macropsini, while contributing to the resolution of systematic issues involving five of their genera. To this task, the mitogenomes of 26 species of the tribe were sequenced and characterized, and their phylogenetic relationships were reconstructed. The results revealed that the nucleotide composition of mitochondrial genes in these 26 species was significantly skewed toward A and T. Codons ending with T or A in relative synonymous codon usage were significantly more prevalent than those ending with C or G. The parity plot, neutrality plot, and correspondence analysis revealed that mutation and selective pressure affect codon usage patterns. In the phylogenetic relationships of the Macropsini, the monophyly of Pedionis and Macropsis was well-supported. Meanwhile, Oncopsis revealed paraphyletic regarding Pediopsoides. In conclusion, this research not only contributes the valuable data to the understanding of the mitogenome of the Macropsini but also provides a reference for future investigations on codon usage patterns, potential adaptive evolution, and the phylogeny of the mitogenome within the subfamily Eurymelinae.

The protein domains of vertebrate species in which selection is more effective have greater intrinsic structural disorder.

The nearly neutral theory of molecular evolution posits variation among species in the effectiveness of selection. In an idealized model, the census population size determines both this minimum magnitude of the selection coefficient required for deleterious variants to be reliably purged, and the amount of neutral diversity. Empirically, an 'effective population size' is often estimated from the amount of putatively neutral genetic diversity and is assumed to also capture a species' effectiveness of selection. A potentially more direct measure of the effectiveness of selection is the degree to which selection maintains preferred codons. However, past metrics that compare codon bias across species are confounded by among-species variation in %GC content and/or amino acid composition. Here, we propose a new Codon Adaptation Index of Species (CAIS), based on Kullback-Leibler divergence, that corrects for both confounders. We demonstrate the use of CAIS correlations, as well as the Effective Number of Codons, to show that the protein domains of more highly adapted vertebrate species evolve higher intrinsic structural disorder.

Evolution is the process through which populations change over time, starting with mutations in the genetic sequence of an organism. Many of these mutations harm the survival and reproduction of an organism, but only by a very small amount. Some species, especially those with large populations, can purge these slightly harmful mutations more effectively than other species. This fact has been used by the 'drift barrier theory' to explain various profound differences amongst species, including differences in biological complexity. In this theory, the effectiveness of eliminating slightly harmful mutations is specified by an 'effective' population size, which depends on factors beyond just the number of individuals in the population. Effective population size is normally calculated from the amount of time a 'neutral' mutation (one with no effect at all) stays in the population before becoming lost or taking over. Estimating this time requires both representative data for genetic diversity and knowledge of the mutation rate. A major limitation is that these data are unavailable for most species. A second limitation is that a brief, temporary reduction in the number of individuals has an oversized impact on the metric, relative to its impact on the number of slighly harmful mutations accumulated. Weibel, Wheeler et al. developed a new metric to more directly determine how effectively a species purges slightly harmful mutations. Their approach is based on the fact that the genetic code has 'synonymous' sequences. These sequences code for the same amino acid building block, with one of these sequences being only slightly preferred over others. The metric by Weibel, Wheeler et al. quantifies the proportion of the genome from which less preferred synonymous sequences have been effectively purged. It judges a population to have a higher effective population size when the usage of synonymous sequences departs further from the usage predicted from mutational processes. The researchers expected that natural selection would favour 'ordered' proteins with robust three-dimensional structures, i.e., that species with a higher effective population size would tend to have more ordered versions of a protein. Instead, they found the opposite: species with a higher effective population size tend to have more disordered versions of the same protein. This changes our view of how natural selection acts on proteins. Why species are so different remains a fundamental question in biology. Weibel, Wheeler et al. provide a useful tool for future applications of drift barrier theory to a broad range of ways that species differ.

New isolate of sweet potato virus 2 from Ipomoea nil: molecular characterization, codon usage bias, and phylogenetic analysis based on complete genome.

BACKGROUND: Viral diseases of sweet potatoes are causing severe crop losses worldwide. More than 30 viruses have been identified to infect sweet potatoes among which the sweet potato latent virus (SPLV), sweet potato mild speckling virus (SPMSV), sweet potato virus G (SPVG) and sweet potato virus 2 (SPV2) have been recognized as distinct species of the genus Potyvirus in the family Potyviridae. The sweet potato virus 2 (SPV2) is a primary pathogen affecting sweet potato crops. METHODS: In this study, we detected an SPV2 isolate (named SPV2-LN) in Ipomoea nil in China. The complete genomic sequence of SPV2-LN was obtained using sequencing of small RNAs, RT-PCR, and RACE amplification. The codon usage, phylogeny, recombination analysis and selective pressure analysis were assessed on the SPV2-LN genome. RESULTS: The complete genome of SPV2-LN consisted of 10,606 nt (GenBank No. OR842902), encoding 3425 amino acids. There were 28 codons in the SPV2-LN genome with a relative synonymous codon usage (RSCU) value greater than 1, of which 21 end in A/U. Among the 12 proteins of SPV2, P3 and P3N-PIPO exhibited the highest variability in their amino acid sequences, while P1 was the most conserved, with an amino acid sequence identity of 87-95.3%. The phylogenetic analysis showed that 21 SPV2 isolates were clustered into four groups, and SPV2-LN was clustered together with isolate yu-17-47 (MK778808) in group IV. Recombination analysis indicated no major recombination sites in SPV2-LN. Selective pressure analysis showed dN/dS of the 12 proteins of SPV2 were less than 1, indicating that all were undergoing negative selection, except for P1N-PISPO. CONCLUSION: This study identified a sweet potato virus, SPV2-LN, in Ipomoea nil. Sequence identities and genome analysis showed high similarity between our isolate and a Chinese isolate, yu-17-47, isolated from sweet potato. These results will provide a theoretical basis for understanding the genetic evolution and viral spread of SPV2.

Codon Usage Bias: A Potential Factor Affecting VGLUT Developmental Expression and Protein Evolution.

More and more attention has been paid to the role of synonymous substitution in evolution, in which codon usage preference can affect gene expression distribution and protein structure and function. Vesicular glutamate transporter (VGLUT) consists of three isoforms, among which VGLUT3 is significantly different from other VGLUTs in functional importance, expression level, and distribution range, whose reason is still unclear. This study sought to analyze the role of codon preference in VGLUT differentiation. To conduct an evolutionary analysis of the three VGLUTs, this paper uses bioinformatics research methods to analyze the coding sequences of the three VGLUTs in different species and compare the codon usage patterns. Furthermore, the differences among the three VGLUTs were analyzed by combining functional importance, expression level, distribution range, gene structure, protein relationship network, expression at specific developmental stages, and phylogenetic tree, and the influence of codon usage pattern was explored. The results showed that the VGLUT with greater codon preference had less functional importance, lower expression levels, more peripheral distribution away from the CNS, smaller exon density of gene, less conserved and farther away from the CDS region miRNA regulatory sites, simpler and less tight protein interaction networks, delayed developmental expression, and more distant evolutionary relationships. Codon usage preference is a potential factor affecting VGLUT developmental expression and protein evolution.

Decoding the origins, spread, and global risks of mcr-9 gene.

BACKGROUND: The global spread of the plasmid-mediated mcr (mobilized colistin resistance) gene family presents a significant threat to the efficacy of colistin, a last-line defense against numerous Gram-negative pathogens. The mcr-9 is the second most prevalent variant after mcr-1. METHODS: A dataset of 698 mcr-9-positive isolates from 44 countries is compiled. The historical trajectory of the mcr-9 gene is reconstructed using Bayesian analysis. The effective reproduction number is used innovatively to study the transmission dynamics of this mobile-drug-resistant gene. FINDINGS: Our investigation traces the origins of mcr-9 back to the 1960s, revealing a subsequent expansion from Western Europe to the America and East Asia in the late 20th century. Currently, its transmissibility remains high in Western Europe. Intriguingly, mcr-9 likely emerged from human-associated Salmonella and exhibits a unique propensity for transmission within the Enterobacter. Our research provides a new perspective that this host preference may be driven by codon usage biases in plasmids. Specifically, mcr-9-carrying plasmids prefer the nucleotide C over T compared to mcr-1-carrying plasmids among synonymous codons. The same bias is seen in Enterobacter compared to Escherichia (respectively as their most dominant genus). Furthermore, we uncovered fascinating patterns of coexistence between different mcr-9 subtypes and other resistance genes. Characterized by its low colistin resistance, mcr-9 has used this seemingly benign feature to silently circumnavigate the globe, evading conventional detection methods. However, colistin-resistant Enterobacter strains with high mcr-9 expression have emerged clinically, implying a strong risk of mcr-9 evolving into a global "true-resistance-gene". INTERPRETATION: This study explores the mcr-9 gene, emphasizing its origin, adaptability, and dissemination potential. Given the high mcr-9 expression colistin-resistant strains was observed in clinically the prevalence of mcr-9 poses a significant challenge to drug resistance prevention and control within the One Health framework. FUNDING: This work was partially supported by the National Natural Science Foundation of China (Grant No. 32141001 and 81991533).

Genetic analysis of tomato brown rugose fruit virus reveals evolutionary adaptation and codon usage bias patterns.

Tomato brown rugose fruit virus (ToBRFV) poses a significant threat to tomato production worldwide, prompting extensive research into its genetic diversity, evolutionary dynamics, and adaptive strategies. In this study, we conducted a comprehensive analysis of ToBRFV at the codon level, focusing on codon usage bias, selection pressures, and evolutionary patterns across multiple genes. Our analysis revealed distinct patterns of codon usage bias and selection pressures within the ToBRFV genome, with varying levels of genetic diversity and evolutionary constraints among different genes. We observed a transition/transversion bias of 2.07 across the entire ToBRFV genome, with the movement protein (MP) gene exhibiting the highest transition/transversion bias and SNP density, suggesting potential evolutionary pressures or a higher mutation rate in this gene. Furthermore, our study identified episodic positive selection primarily in the MP gene, highlighting specific codons subject to adaptive changes in response to host immune pressures or environmental factors. Comparative analysis of codon usage bias in the coat protein (CP) and RNA-dependent RNA polymerase (RdRp) genes revealed gene-specific patterns reflecting functional constraints and adaptation to the host's translational machinery. Our findings provide valuable insights into the molecular mechanisms driving ToBRFV evolution and adaptation, with implications for understanding viral pathogenesis, host-virus interactions, and the development of control strategies. Future research directions include further elucidating the functional significance of codon usage biases, exploring the role of episodic positive selection in viral adaptation, and leveraging these insights to inform the development of effective antiviral strategies and crop protection measures.

Analysis of Codon Usage Bias in the Plastid Genome of Diplandrorchis sinica (Orchidaceae).

In order to understand the bias and main affecting factors of codon usage in the plastid genome of Diplandrorchis sinica, which is a rare and endangered plant species in the Orchidaceae family, the complete plastid genome sequence of D. sinica was downloaded from the GenBank database and 20 protein-coding sequences that met the analysis requirements were finally selected. The GC content, length of the amino acid (Laa), relative synonymous codon usage (RSCU), and effective number of codon (ENC) of each gene and codon were calculated using the CodonW and EMBOSS online programs. Neutral plot analysis, ENC-plot analysis, PR2-plot analysis, and correspondence analysis were performed using Origin Pro 2024 software, and correlation analysis between various indicators was performed using SPSS 23.0 software. The results showed that the third base of the codon in the plastid genome of D. sinica was rich in A and T, with a GC3 content of 27%, which was lower than that of GC1 (45%) and GC2 (39%). The ENC value ranged from 35 to 57, with an average of 47. The codon usage bias was relatively low, and there was a significant positive correlation between ENC and GC3. There were a total of 32 codons with RSCU values greater than 1, of which 30 ended with either A or U. There were a total of nine optimal codons identified, namely, UCU, UCC, UCA, GCA, UUG, AUA, CGU, CGA, and GGU. This study indicated that the dominant factor affecting codon usage bias in the plastid genome of D. sinica was natural selection pressure, while the impact of base mutations was limited. The codon usage patterns were not closely related to gene types, and the distribution of photosynthetic system genes and ribosomal protein-coding gene loci was relatively scattered, indicating significant differences in the usage patterns of these gene codons. In addition, the codon usage patterns may not be related to whether the plant is a photosynthetic autotrophic or heterotrophic nutritional type. The results of this study could provide scientific references for the genomic evolution and phylogenetic research of plant species in the family Orchidaceae.

Codon Usage Analysis Reveals Distinct Evolutionary Patterns and Host Adaptation Strategies in Duck Hepatitis Virus 1 (DHV-1) Phylogroups.

Duck hepatitis virus 1 (DHV-1) is a major threat to the global poultry industry, causing significant economic losses due to high mortality rates in young ducklings. To better understand the evolution and host adaptation strategies of DHV-1, we conducted a comprehensive codon usage analysis of DHV-1 genomes. Our phylogenetic analysis revealed three well-supported DHV-1 phylogroups (Ia, Ib, and II) with distinct genetic diversity patterns. Comparative analyses of the codon usage bias and dinucleotide abundance uncovered a strong preference for A/U-ended codons and a biased pattern of dinucleotide usage in the DHV-1 genome, with CG dinucleotides being extremely underrepresented. Effective number of codons (ENC) analysis indicated a low codon usage bias in the DHV-1 ORF sequences, suggesting adaptation to host codon usage preferences. PR2 bias, ENC plot, and neutrality analyses revealed that both mutation pressure and natural selection influence the codon usage patterns of DHV-1. Notably, the three DHV-1 phylogroups exhibited distinct evolutionary trends, with phylogroups Ia and Ib showing evidence of neutral evolution accompanied by selective pressure, while the phylogroup II evolution was primarily driven by random genetic drift. Comparative analysis of the codon usage indices (CAI, RCDI, and SiD) among the phylogroups highlighted significant differences between subgroups Ia and Ib, suggesting distinct evolutionary pressures or adaptations influencing their codon usage. These findings contribute to our understanding of DHV-1 evolution and host adaptation, with potential implications for the development of effective control measures and vaccines.

Epi-Clock: A sensitive platform to help understand pathogenic disease outbreaks and facilitate the response to future outbreaks of concern.

To predict potential epidemic outbreaks, we tested our strategy, Epi-Clock, which applies the novel ZHU algorithm to different SARS-CoV-2 datasets before outbreaks to search for significant mutational accumulation patterns correlated with outbreak events. Surprisingly, some inter-species genetic distances in Coronaviridae may represent intermediate states of different species or subspecies in the evolutionary history of Coronaviridae. The insertions and deletions in whole-genome sequences between different hosts were separately associated with important roles in host transmission and shifts in Coronaviridae. Furthermore, we believe that non-nucleosomal DNA may play a dominant role in the divergence of different lineages of SARS-CoV-2 in different regions of the world owing to the lack of nucleosome protection. We suggest that strong selective variation among different lineages of SARS-CoV-2 is required to produce strong codon usage bias, which appears in B.1.640.2 and B.1.617.2 (Delta). Notably, we found that an increasing number of other types of substitutions, such as those resulting from the hitchhiking effect, accumulated, especially in the pre-breakout phase, although some of the previous substitutions were replaced by other dominant genotypes. From most validations, we could accurately predict the potential pre-phase of outbreaks with a median interval of 5 days.

Understanding the nucleotide composition and patterns of codon usage in the expression of human oral cancer genes.

Oral squamous cell carcinoma (OSCC) is primarily known as oral cancer (OC) that mostly occurs in mouth, lips and tongue. Mutations in some of the genes cause OC and some genes are risk factors for progression of OC. In this study, we analyzed the compositional features and pattern of codon usage in genes involved in OC using computational method as no work was reported yet. Compositional features suggested that the overall GC content was higher i.e. genes were GC rich. Effective number of codons (ENC) values ranged from 34.6 to 55.9 with a mean value of 49.03±4.22 representing low codon usage bias (CUB). Correspondence analysis (COA) suggested that the codon usage pattern was different in different genes. In genes associated with OC, highly significant correlation was observed between GC12 and GC3 (r=0.454, p<0.01) suggesting that directional mutation affected all the three codon positions. This is the first report on pattern of codon usage pattern on genes involved in OC, which not only alludes a new perspective for elucidating the mechanisms of biased usage of synonymous codons but also provide valuable clues for molecular genetic engineering.

Morphological Structure Identification, Comparative Mitochondrial Genomics and Population Genetic Analysis toward Exploring Interspecific Variations and Phylogenetic Implications of Malus baccata 'ZA' and Other Species.

Malus baccata, a valuable germplasm resource in the genus Malus, is indigenous to China and widely distributed. However, little is known about the lineage composition and genetic basis of 'ZA', a mutant type of M. baccata. In this study, we compared the differences between 'ZA' and wild type from the perspective of morphology and ultrastructure and analyzed their chloroplast pigment content based on biochemical methods. Further, the complete mitogenome of M. baccata 'ZA' was assembled and obtained by next-generation sequencing. Subsequently, its molecular characteristics were analyzed using Geneious, MISA-web, and CodonW toolkits. Furthermore, by examining 106 Malus germplasms and 42 Rosaceae species, we deduced and elucidated the evolutionary position of M. baccata 'ZA', as well as interspecific variations among different individuals. In comparison, the total length of the 'ZA' mitogenome (GC content: 45.4%) is 374,023 bp, which is approximately 2.33 times larger than the size (160,202 bp) of the plastome (GC: 36.5%). The collinear analysis results revealed abundant repeats and genome rearrangements occurring between different Malus species. Additionally, we identified 14 plastid-driven fragment transfer events. A total of 54 genes have been annotated in the 'ZA' mitogenome, including 35 protein-coding genes, 16 tRNAs, and three rRNAs. By calculating nucleotide polymorphisms and selection pressure for 24 shared core mitochondrial CDSs from 42 Rosaceae species (including 'ZA'), we observed that the nad3 gene exhibited minimal variation, while nad4L appeared to be evolving rapidly. Population genetics analysis detected a total of 1578 high-quality variants (1424 SNPs, 60 insertions, and 94 deletions; variation rate: 1/237) among samples from 106 Malus individuals. Furthermore, by constructing phylogenetic trees based on both Malus and Rosaceae taxa datasets, it was preliminarily demonstrated that 'ZA' is closely related to M. baccata, M. sieversii, and other proximate species in terms of evolution. The sequencing data obtained in this study, along with our findings, contribute to expanding the mitogenomic resources available for Rosaceae research. They also hold reference significance for molecular identification studies as well as conservation and breeding efforts focused on excellent germplasms.

Comparative Analysis of Codon Usage Bias in Six Eimeria Genomes.

The codon usage bias (CUB) of genes encoded by different species' genomes varies greatly. The analysis of codon usage patterns enriches our comprehension of genetic and evolutionary characteristics across diverse species. In this study, we performed a genome-wide analysis of CUB and its influencing factors in six sequenced Eimeria species that cause coccidiosis in poultry: Eimeria acervulina, Eimeria necatrix, Eimeria brunetti, Eimeria tenella, Eimeria praecox, and Eimeria maxima. The GC content of protein-coding genes varies between 52.67% and 58.24% among the six Eimeria species. The distribution trend of GC content at different codon positions follows GC1 > GC3 > GC2. Most high-frequency codons tend to end with C/G, except in E. maxima. Additionally, there is a positive correlation between GC3 content and GC3s/C3s, but a significantly negative correlation with A3s. Analysis of the ENC-Plot, neutrality plot, and PR2-bias plot suggests that selection pressure has a stronger influence than mutational pressure on CUB in the six Eimeria genomes. Finally, we identified from 11 to 15 optimal codons, with GCA, CAG, and AGC being the most commonly used optimal codons across these species. This study offers a thorough exploration of the relationships between CUB and selection pressures within the protein-coding genes of Eimeria species. Genetic evolution in these species appears to be influenced by mutations and selection pressures. Additionally, the findings shed light on unique characteristics and evolutionary traits specific to the six Eimeria species.

Exploring Codon Usage Patterns and Influencing Factors in Ranavirus DNA Polymerase Genes.

Ranaviruses, members of the genus Ranavirus within the family Iridoviridae, have become a significant concern for amphibian populations globally, along with other cold-blooded vertebrates, due to their emergence as a significant threat. We employed bioinformatics tools to examine the codon usage patterns in 61 DNA pol genes from Ranavirus, Lymphocystivirus, Megalocytivirus, and two unclassified ranaviruses, as no prior studies had been conducted on this topic. The results showed a slight or low level of codon usage bias (CUB) in the DNA pol genes of Ranavirus. Relative synonymous codon usage (RSCU) analysis indicated that the predominant codons favored in Ranavirus DNA pol genes terminate with C or G. Correlation analysis examining nucleotide content, third codon position, effective number of codons (ENC), correspondence analysis (COA), Aroma values, and GRAVY values indicated that the CUB across DNA pol genes could be influenced by both mutation pressure and natural selection. The neutrality plot indicated that natural selection is the primary factor driving codon usage. Furthermore, the analysis of the codon adaptation index (CAI) illustrated the robust adaptability of Ranavirus DNA pol genes to their hosts. Analysis of the relative codon deoptimization index (RCDI) suggested that Ranavirus DNA pol genes underwent greater selection pressure from their hosts. These findings will aid in comprehending the factors influencing the evolution and adaptation of Ranavirus to its hosts.

Genomic factors shaping codon usage across the Saccharomycotina subphylum.

Codon usage bias, or the unequal use of synonymous codons, is observed across genes, genomes, and between species. It has been implicated in many cellular functions, such as translation dynamics and transcript stability, but can also be shaped by neutral forces. We characterized codon usage across 1,154 strains from 1,051 species from the fungal subphylum Saccharomycotina to gain insight into the biases, molecular mechanisms, evolution, and genomic features contributing to codon usage patterns. We found a general preference for A/T-ending codons and correlations between codon usage bias, GC content, and tRNA-ome size. Codon usage bias is distinct between the 12 orders to such a degree that yeasts can be classified with an accuracy greater than 90% using a machine-learning algorithm. We also characterized the degree to which codon usage bias is impacted by translational selection. We found it was influenced by a combination of features, including the number of coding sequences, BUSCO count, and genome length. Our analysis also revealed an extreme bias in codon usage in the Saccharomycodales associated with a lack of predicted arginine tRNAs that decode CGN codons, leaving only the AGN codons to encode arginine. Analysis of Saccharomycodales gene expression, tRNA sequences, and codon evolution suggests that avoidance of the CGN codons is associated with a decline in arginine tRNA function. Consistent with previous findings, codon usage bias within the Saccharomycotina is shaped by genomic features and GC bias. However, we find cases of extreme codon usage preference and avoidance along yeast lineages, suggesting additional forces may be shaping the evolution of specific codons.

Repetitive Sequences, Codon Usage Bias and Phylogenetic Analysis of the Plastome of Miliusa glochidioides.

Annonaceae is the largest family in Magnoliales, exhibiting the greatest diversity among and within genera. In this study, we conducted an analysis of repetitive sequences and codon usage bias in the previously acquired plastome of Miliusa glochidioides. Using a concatenated dataset of shared genes, we constructed the phylogenetic relationships among 27 Annonaceae species. The results showed that the size of the plastomes in the Annonaceae ranged from 159 to 202 kb, with the size of the inverted repeat region ranging from 40 to 65 kb. Within the plastome of M. glochidioides, we identified 42 SSRs, 36 tandem repeats, and 9 dispersed repeats. These SSRs consist of three nucleotide types and eight motif types, with a preference for A/T bases, primarily located in the large single-copy regions and intergenic spacers. Tandem and dispersed repeat sequences were predominantly detected in the IR region. Through codon usage bias analysis, we identified 30 high-frequency codons and 11 optimal codons. The plastome of M. glochidioides demonstrated relatively weak codon usage bias, favoring codons with A/T endings, primarily influenced by natural selection. Phylogenetic analysis revealed that all four subfamilies formed monophyletic groups, with Cananga odorata (Ambavioideae) and Anaxagorea javanica (Anaxagoreoideae) successively nested outside Annonoideae + Malmeoideae. These findings improve our understanding of the plastome of M. glochidioides and provide additional insights for studying plastome evolution in Annonaceae.

Patterns in Genome-Wide Codon Usage Bias in Representative Species of Lycophytes and Ferns.

The latest research shows that ferns and lycophytes have distinct evolutionary lineages. The codon usage patterns of lycophytes and ferns have not yet been documented. To investigate the gene expression profiles across various plant lineages with respect to codon usage, analyze the disparities and determinants of gene evolution in primitive plant species, and identify appropriate exogenous gene expression platforms, the whole-genome sequences of four distinct species were retrieved from the NCBI database. The findings indicated that Ceratopteris richardii, Adiantum capillus-veneris, and Selaginella moellendorffii exhibited an elevated A/U content in their codon base composition and a tendency to end with A/U. Additionally, S. capillus-veneris had more C/G in its codons and a tendency to end with C/G. The ENC values derived from both ENC-plot and ENC-ratio analyses deviated significantly from the standard curves, suggesting that the codon usage preferences of these four species were primarily influenced by genetic mutations and natural selection, with natural selection exerting a more prominent influence. This finding was further supported by PR2-Plot, neutrality plot analysis, and COA. A combination of RSCU and ENC values was used as a reference criterion to rank the codons and further identify the optimal codons. The study identified 24 high-frequency codons in C. richardii, A. capillus-veneris, and Diphasiastrum complanatum, with no shared optimal codons among the four species. Arabidopsis thaliana and Ginkgo biloba exhibited similar codon preferences to the three species, except for S. moellendorffii. This research offers a theoretical framework at the genomic codon level for investigating the phylogenetic relationships between lycophytes and ferns, shedding light on gene codon optimization and its implications for genetic engineering in breeding.

Analysis of Codon Usage Bias in Chloroplast Genomes of Dryas octopetala var. asiatica (Rosaceae).

Dryas octopetala var. asiatica, a dwarf shrub belonging to the Rosaceae family and native to Asia, exhibits notable plasticity in photosynthesis in response to temperature variations. However, the codon usage patterns and factors influencing them in the chloroplast genome of this species have not yet been documented. This study sequenced and assembled the complete genome of D. octopetala var. asiatica. The annotated genes in the chloroplast genome were analyzed for codon composition through multivariate statistical methods including a neutrality plot, a parity rule 2 (PR2) bias plot, and an effective number of codons (ENC) plot using CodonW 1.4.2 software. The results indicated that the mean GC content of 53 CDSs was 38.08%, with the average GC content at the third codon base position being 27.80%, suggesting a preference for A/U(T) at the third codon position in chloroplast genes. Additionally, the chloroplast genes exhibited a weak overall codon usage bias (CUB) based on ENC values and other indicators. Correlation analysis showed a significant negative correlation between ENC value and GC2, an extremely positive correlation with GC3, but no correlation with GC1 content. These findings highlight the importance of the codon composition at the third position in influencing codon usage bias. Furthermore, our analysis indicated that the CUB of the chloroplast genome of D. octopetala var. asiatica was primarily influenced by natural selection and other factors. Finally, this study identified UCA, CCU, GCU, AAU, GAU, and GGU as the optimal codons. These results offer a foundational understanding for genetic modification and evolutionary dynamics of the chloroplast genome of D. octopetala var. asiatica.

Differentially used codons among essential genes in bacteria identified by machine learning-based analysis.

Codon usage bias (CUB), the uneven usage of synonymous codons encoding the same amino acid, differs among genes within and across bacteria genomes. CUB is known to be influenced by gene expression and accordingly, CUB differs between the high-expression and low-expression genes in several bacteria. In this article, we have extended codon usage study considering gene essentiality as a feature. Using machine learning (ML) based approaches, we have analysed Relative Synonymous Codon Usage (RSCU) values between essential and non-essential genes in Escherichia coli and thirty-four other bacterial genomes whose gene essentiality features were available in public databases. We observed significant differences in codon usage patterns between essential and non-essential genes for majority of the bacterial genomes and accordingly, ML based classifiers achieved high area under curve (AUC) scores, with a minimum score of 70.0 across twenty-eight organisms. Further, importance of the codons towards classifying genes found to differ among the codons in each genome. Arg codon CGT and Gly codon GGT were observed to be the most preferred codons among essential genes in Escherichia coli. Interestingly, some of the codons like CGT, ATA, GGT and GGG observed to be contributing consistently towards classifying essential genes across thirty-five bacteria genomes studied. In other hand, codons TGY and CAY encoding amino acids Cys and His respectively were among the least contributing codons towards classification among all these bacteria. This study demonstrates the gene essentiality based differences in synonymous codon usage in bacteria genomes and presents a common codon usage pattern across bacteria.

Codon usage bias in yeasts and its correlation with gene expression, growth temperature, and protein structure.

Codon usage bias (CUB) has been described in viruses, prokaryotes, and eukaryotes and has been linked to several cellular and environmental factors, such as the organism's growth temperature, gene expression levels, and regulation of protein synthesis and folding. Most of the studies in this area have been conducted in bacteria and higher eukaryotes, in some cases with different results. In this study, a comparative analysis of CUB in yeasts isolated from cold and template environments was performed in order to evaluate the correlation of CUB with yeast optimal temperature of growth (OTG), gene expression levels, cellular function, and structure of encoded proteins. Among the main findings, highly expressed ORFs tend to have a more similar CUB within and between yeasts, and a direct correlation between codons ending in C and expression level was generally found. A low correspondence between CUB and OTG was observed, with an inverse correlation for some codons ending in C. The clustering of yeasts based on their CUB partially aligns with their OTG, being more consistent for yeasts with lower OTG. In most yeasts, the abundance of preferred codons was generally lower at the 5' end of ORFs, higher in segments encoding beta strand, lower in segments encoding extracellular and transmembrane regions, and higher in "translation" and "energy metabolism" pathways, especially in highly expressed ORFs. Based on our findings, it is suggested that the abundance and distribution of preferred and non-preferred codons along mRNAs contribute to proper protein folding and functionality by regulating protein synthesis rates, becoming a more important factor under conditions that require faster protein synthesis in yeasts.

Molecular Evolution of Protein Sequences and Codon Usage in Monkeypox Viruses.

The monkeypox virus (mpox virus, MPXV) epidemic in 2022 has posed a significant public health risk. Yet, the evolutionary principles of MPXV remain largely unknown. Here, we examined the evolutionary patterns of protein sequences and codon usage in MPXV. We first demonstrated the signal of positive selection in OPG027, specifically in the Clade I lineage of MPXV. Subsequently, we discovered accelerated protein sequence evolution over time in the variants responsible for the 2022 outbreak. Furthermore, we showed strong epistasis between amino acid substitutions located in different genes. The codon adaptation index (CAI) analysis revealed that MPXV genes tended to use more non-preferred codons compared to human genes, and the CAI decreased over time and diverged between clades, with Clade I > IIa and IIb-A > IIb-B. While the decrease in fatality rate among the three groups aligned with the CAI pattern, it remains unclear whether this correlation was coincidental or if the deoptimization of codon usage in MPXV led to a reduction in fatality rates. This study sheds new light on the mechanisms that govern the evolution of MPXV in human populations.