Mutation and selection cause codon usage and bias in mitochondrial genomes of ribbon worms (Nemertea)

Intraspecific and interspecific variations in the synonymous codon usage in mitochondrial genomes of 8 pleurotus strains

In this study, we investigated the codon bias of twelve mitochondrial core protein coding genes (PCGs) in eight Pleurotus strains, two of which are from the same species. The results revealed that the codons of all Pleurotus strains had a preference for ending in A/T. Furthermore, the correlation between codon base compositions and codon adaptation index (CAI), codon bias index (CBI) and frequency of optimal codons (FOP) indices was also detected, implying the influence of base composition on codon bias. The two P. ostreatus species were found to have differences in various base bias indicators. The average effective number of codons (ENC) of mitochondrial core PCGs of Pleurotus was found to be less than 35, indicating strong codon preference of mitochondrial core PCGs of Pleurotus. The neutrality plot analysis and PR2-Bias plot analysis further suggested that natural selection plays an important role in Pleurotus codon bias. Additionally, six to ten optimal codons (ΔRSCU > 0.08 and RSCU > 1) were identified in eight Pleurotus strains, with UGU and ACU being the most widely used optimal codons in Pleurotus. Finally, based on the combined mitochondrial sequence and RSCU value, the genetic relationship between different Pleurotus strains was deduced, showing large variations between them. This research has improved our understanding of synonymous codon usage characteristics and evolution of this important fungal group.

Codon Usage Bias Analysis in Macronuclear Genomes of Ciliated Protozoa

Ciliated protozoa (ciliates) are unicellular eukaryotes, several of which are important model organisms for molecular biology research. Analyses of codon usage bias (CUB) of the macronuclear (MAC) genome of ciliates can promote a better understanding of the genetic mode and evolutionary history of these organisms and help optimize codons to improve gene editing efficiency in model ciliates. In this study, the following indices were calculated: the guanine-cytosine (GC) content, the frequency of the nucleotides at the third position of codons (T3, C3, A3, G3), the effective number of codons (ENc), GC content at the 3rd position of synonymous codons (GC3s), and the relative synonymous codon usage (RSCU). Parity rule 2 plot analysis, Neutrality plot analysis, ENc plot analysis, and correlation analysis were employed to explore the main influencing factors of CUB. The results showed that the GC content in the MAC genomes of each of 21 ciliate species, the genomes of which were relatively complete, was lower than 50%, and the base compositions of GC and GC3s were markedly distinct. Synonymous codon analysis revealed that the codons in most of the 21 ciliates ended with A or T and four codons were the general putative optimal codons. Collectively, our results indicated that most of the ciliates investigated preferred using the codons with anof AT-ending and that codon usage bias was affected by gene mutation and natural selection.

Analysis of synonymous codon usage patterns in mitochondrial genomes of nine Amanita species

Introduction

Codon basis is a common and complex natural phenomenon observed in many kinds of organisms.

Methods

In the present study, we analyzed the base bias of 12 mitochondrial core protein-coding genes (PCGs) shared by nine Amanita species.

Results

The results showed that the codons of all Amanita species tended to end in A/T, demonstrating the preference of mitochondrial codons of Amanita species for a preference for this codon. In addition, we detected the correlation between codon base composition and the codon adaptation index (CAI), codon bias index (CBI), and frequency of optimal codons (FOP) indices, indicating the influence of base composition on codon bias. The average effective number of codons (ENC) of mitochondrial core PCGs of Amanita is 30.81, which is <35, demonstrating the strong codon preference of mitochondrial core PCGs of Amanita. The neutrality plot analysis and PR2-Bias plot analysis further demonstrated that natural selection plays an important role in Amanita codon bias. In addition, we obtained 5–10 optimal codons (ΔRSCU > 0.08 and RSCU > 1) in nine Amanita species, and GCA and AUU were the most widely used optimal codons. Based on the combined mitochondrial sequence and RSCU value, we deduced the genetic relationship between different Amanita species and found large variations between them.

Discussion

This study promoted the understanding of synonymous codon usage characteristics and evolution of this important fungal group.

Evolution of codon usage in Taenia saginata genomes and its impact on the host

The beef tapeworm, also known as Taenia saginata, is a zoonotic tapeworm from the genus Taenia in the order Cyclophyllidea. Taenia saginata is a food-borne zoonotic parasite with a worldwide distribution. It poses serious health risks to the host and has a considerable negative socioeconomic impact. Previous studies have explained the population structure of T. saginata within the evolutionary time scale and adaptive evolution. However, it is still unknown how synonymous codons are used by T. saginata. In this study, we used 90 T. saginata strains, applying the codon usage bias (CUB). Both base content and relative synonymous codon usage (RSCU) analysis revealed that AT-ended codons were more frequently used in the genome of T. saginata. Further low CUB was observed from the effective number of codons (ENC) value. The neutrality plot analysis suggested that the dominant factor of natural selection was involved in the structuring of CUB in T. saginata. Further analysis showed that T. saginata has adapted host-specific codon usage patterns to sustain successful replication and transmission chains within hosts (Bos taurus and Homo sapiens). Generally, both natural selection and mutational pressure have an impact on the codon usage patterns of the protein-coding genes in T. saginata. This study is important because it characterized the codon usage pattern in the T. saginata genomes and provided the necessary data for a basic evolutionary study on them.

Analysis of codon usage bias of lumpy skin disease virus causing livestock infection

Lumpy skin disease virus (LSDV) causes lumpy skin disease (LSD) in livestock, which is a double-stranded DNA virus that belongs to the genus Capripoxvirus of the family Poxviridae. LSDV is an important poxvirus that has spread out far and wide to become distributed worldwide. It poses serious health risks to the host and causes considerable negative socioeconomic impact on farmers financially and on cattle by causing ruminant-related diseases. Previous studies explained the population structure of the LSDV within the evolutionary time scale and adaptive evolution. However, it is still unknown and remains enigmatic as to how synonymous codons are used by the LSDV. Here, we used 53 LSDV strains and applied the codon usage bias (CUB) analysis to them. Both the base content and the relative synonymous codon usage (RSCU) analysis revealed that the AT-ended codons were more frequently used in the genome of LSDV. Further low codon usage bias was calculated from the effective number of codons (ENC) value. The neutrality plot analysis suggested that the dominant factor of natural selection played a role in the structuring of CUB in LSDV. Additionally, the results from a comparative analysis suggested that the LSDV has adapted host-specific codon usage patterns to sustain successful replication and transmission chains within hosts (Bos taurus and Homo sapiens). Both natural selection and mutational pressure have an impact on the codon usage patterns of the protein-coding genes in LSDV. This study is important because it has characterized the codon usage pattern in the LSDV genomes and has provided the necessary data for a basic evolutionary study on them.

The complete mitochondrial genome of Talpa martinorum (Mammalia: Talpidae), a mole species endemic to Thrace: genome content and phylogenetic considerations

The complete mitogenome sequence of Talpa martinorum, a recently described Balkan endemic mole, was assembled from next generation sequence data. The mitogenome is similar to that of the three other Talpa species sequenced to date, being 16,835 bp in length, and containing 13 protein-coding genes, two ribosomal RNA genes, 22 transfer RNA genes, an origin of L-strand replication, and a control region or D-loop. Compared to other Talpa mitogenomes sequenced to date, that of T. martinorum differs in the length of D-loop and stop codon usage. TAG and T-- are the stop codons for the ND1 and ATP8 genes, respectively, in T. martinorum, whilst TAA acts as a stop codon for both ND1 and ATP8 in the other three Talpa species sequenced. Phylogeny reconstructions based on Maximum Likelihood and Bayesian inference analyses yielded phylogenies with similar topologies, demonstrating that T. martinorum nests within the western lineage of the genus, being closely related to T. aquitania and T. occidentalis.

Codon Usage is Influenced by Compositional Constraints in Genes Associated with Dementia

Dementia is a clinical syndrome characterized by progressive cognitive decline, and the symptoms could be gradual, persistent, and progressive. In the present study, we investigated 47 genes that have been linked to dementia. Compositional, selectional, and mutational forces were seen to be involved. Nucleotide components that influenced A- and GC-affected codon usages bias at all three codon positions. The influence of these two compositional constraints on codon usage bias (CUB) was positive for nucleotide A and negative for GC. Nucleotide A also experienced the highest mutational force, and GC-ending codons were preferred over AT-ending codons. A high bias toward GC-ending codons enhances the gene expression level, evidenced by the positive association between CAI- and GC-ending codons. Unusual behavior of the TTG codon showing an inverse relationship with the GC-ending codon and negative influence of gene expression, behavior contrary to all other GC-ending codons, shows an operative selectional force. Furthermore, parity analysis, higher translational selection value, preference of GC-ending codons over AT-ending codons, and association of gene length with gene expression refer to the dominant role of selection pressure with compositional constraint and mutational force-shaping codon usage.

Strong Selectional Forces Fine-Tune CpG Content in Genes Involved in Neurological Disorders as Revealed by Codon Usage Patterns

Neurodegenerative disorders cause irreversible damage to the neurons and adversely affect the quality of life. Protein misfolding and their aggregation in specific parts of the brain, mitochondrial dysfunction, calcium load, proteolytic stress, and oxidative stress are among the causes of neurodegenerative disorders. In addition, altered metabolism has been associated with neurodegeneration as evidenced by reductions in glutamine and alanine in transient global amnesia patients, higher homocysteine-cysteine disulfide, and lower methionine decline in serum urea have been observed in Alzheimer's disease patients. Neurodegeneration thus appears to be a culmination of altered metabolism. The study's objective is to analyze various attributes like composition, physical properties of the protein, and factors like selectional and mutational forces, influencing codon usage preferences in a panel of genes involved directly or indirectly in metabolism and contributing to neurodegeneration. Various parameters, including gene composition, dinucleotide analysis, Relative synonymous codon usage (RSCU), Codon adaptation index (CAI), neutrality and parity plots, and different protein indices, were computed and analyzed to determine the codon usage pattern and factors affecting it. The correlation of intrinsic protein properties such as the grand average of hydropathicity index (GRAVY), isoelectric point, hydrophobicity, and acidic, basic, and neutral amino acid content has been found to influence codon usage. In genes up to 800 amino acids long, the GC3 content was highly variable, while GC12 content was relatively constant. An optimum CpG content is present in genes to maintain a high expression level as required for genes involved in metabolism. Also observed was a low codon usage bias with a higher protein expression level. Compositional parameters and nucleotides at the second position of codons played essential roles in explaining the extent of bias. Overall analysis indicated that the dominance of selection pressure and compositional constraints and mutational forces shape codon usage.

Mitogenome-wise codon usage pattern from comparative analysis of the first mitogenome of Blepharipa sp. (Muga uzifly) with other Oestroid flies

Uziflies (Family: Tachinidae) are dipteran endoparasites of sericigenous insects which cause major economic loss in the silk industry globally. Here, we are presenting the first full mitogenome of Blepharipa sp. (Acc: KY644698, 15,080 bp, A + T = 78.41%), a dipteran parasitoid of Muga silkworm (Antheraea assamensis) found in the Indian states of Assam and Meghalaya. This study has confirmed that Blepharipa sp. mitogenome gene content and arrangement is similar to other Tachinidae and Sarcophagidae flies of Oestroidea superfamily, typical of ancestral Diptera. Although, Calliphoridae and Oestridae flies have undergone tRNA translocation and insertion, forming unique intergenic spacers (IGS) and overlapping regions (OL) and a few of them (IGS, OL) have been conserved across Oestroidea flies. The Tachinidae mitogenomes exhibit more AT content and AT biased codons in their protein-coding genes (PCGs) than the Oestroidea counterpart. About 92.07% of all (3722) codons in PCGs of this new species have A/T in their 3rd codon position. The high proportion of AT and repeats in the control region (CR) affects sequence coverage, resulting in a short CR (Blepharipa sp.: 168 bp) and a smaller tachinid mitogenome. Our research unveils those genes with a high AT content had a reduced effective number of codons, leading to high codon usage bias. The neutrality test shows that natural selection has a stronger influence on codon usage bias than directed mutational pressure. This study also reveals that longer PCGs (e.g., nad5, cox1) have a higher codon usage bias than shorter PCGs (e.g., atp8, nad4l). The divergence rates increase nonlinearly as AT content at the 3rd codon position increases and higher rate of synonymous divergence than nonsynonymous divergence causes strong purifying selection. The phylogenetic analysis explains that Blepharipa sp. is well suited in the family of insectivorous tachinid maggots. It's possible that biased codon usage in the Tachinidae family reduces the effective number of codons, and purifying selection retains the core functions in their mitogenome, which could help with efficient metabolism in their endo-parasitic life style and survival strategy.

Comprehensive analysis of codon usage pattern in Withania somnifera and its associated pathogens: Meloidogyne incognita and Alternaria alternata

Meloidogyne incognita (Root-knot nematode) and Alternaria alternata (fungus) were among the dominant parasites of the medicinal plant Withania somnifera. Despite the fatal nature of their infection, a comprehensive study to explore their evolution and adaptation is lacking. The present study elucidates evolutionary and codon usage bias analysis of W. somnifera (host plant), M. incognita (root-knot nematode) and A. alternata (fungal parasite). The results of the present study revealed a weak codon usage bias prevalent in all the three organisms. Based on the nucleotide analysis, genome of W. somnifera and M. incognita was found to be A-T biased while A. alternata had GC biased genome. We found high similarity of CUB pattern between host and its nematode pathogen as compared to the fungal pathogen. Inclusively, both the evolutionary forces influenced the CUB in host and its associated pathogens. However, neutrality plot indicated the pervasiveness of natural selection on CUB of the host and its pathogens. Correspondence analysis revealed the dominant effect of mutation on CUB of W. somnifera and M. incognita while natural selection was the main force affecting CUB of A. alternata. Taken together the present study would provide some prolific insight into the role of codon usage bias in the adaptability of pathogens to the host’s environment for establishing parasitic relationship.

Comparative mitogenomics of Clupeoid fish provides insights into the adaptive evolution of mitochondrial oxidative phosphorylation (OXPHOS) genes and codon usage in the heterogeneous habitats

Clupeoid fish can be considered excellent candidates to understand the role of mitochondrial DNA in adaptive evolution, as they have colonized different habitats (marine, brackish, freshwater, tropical and temperate regions) over millions of years. Here, we investigate patterns of tRNA location, codon usage bias, and lineage-specific diversifying selection signals to provide novel insights into how evolutionary improvements of mitochondrial metabolic efficiency have allowed clupeids to adapt to different habitats. Based on whole mitogenome data of 70 Clupeoids with a global distribution we find that purifying selection was the dominant force acting and that the mutational deamination pressure in mtDNA was stronger than the codon/amino acid constraints. The codon usage pattern appears evolved to achieve high translational efficiency (codon/amino acid-related constraints), as indicated by the complementarity of most codons to the GT-saturated tRNA anticodon sites (retained by deamination-induced pressure) and usage of the codons of the tRNA genes situated near to the control region (fixed by deamination pressure) where transcription efficiency was high. The observed shift in codon preference patterns between marine and euryhaline/freshwater Clupeoids indicates possible selection for improved translational efficiency in mitochondrial genes while adapting to low-salinity habitats. This mitogenomic plasticity and enhanced efficiency of the metabolic machinery may have contributed to the evolutionary success and abundance of Clupeoid fish.

Codon usage patterns across seven Rosales species

BACKGROUND

Codon usage bias (CUB) analysis is an effective method for studying specificity, evolutionary relationships, and mRNA translation and discovering new genes among various species. In general, CUB analysis is mainly performed within one species or between closely related species and no such study has been applied among species with distant genetic relationships. Here, seven Rosales species with high economic value were selected to conduct CUB analysis.

RESULTS

The results showed that the average GC1, GC2 and GC3 contents were 51.08, 40.52 and 43.12%, respectively, indicating that the A/T content is more abundant and the Rosales species prefer A/T as the last codon. Neutrality plot and ENc plot analysis revealed that natural selection was the main factor leading to CUB during the evolution of Rosales species. All 7 Rosales species contained three high-frequency codons, AGA, GTT and TTG, encoding Arg, Val and Leu, respectively. The 7 Rosales species differed in high-frequency codon pairs and the distribution of GC3, though the usage patterns of closely related species were more consistent. The results of the biclustering heat map among 7 Rosales species and 20 other species were basically consistent with the results of genome data, suggesting that CUB analysis is an effective method for revealing evolutionary relationships among species at the family or order level. In addition, chlorophytes prefer using G/C as ending codon, while monocotyledonous and dicotyledonous plants prefer using A/T as ending codon.

CONCLUSIONS

The CUB pattern among Rosales species was mainly affected by natural selection. This work is the first to highlight the CUB patterns and characteristics of Rosales species and provides a new perspective for studying genetic relationships across a wide range of species.

Compositional features and pattern of codon usage for mitochondrial CO genes among reptiles

The phenomenon of non-random occurrence of synonymous nucleotide triplets (codons) in the coding sequences of genes is the codon usage bias (CUB). In this study, we used bioinformatic tool kit to analyze the compositional pattern and CUB of mitogenes namely COI, COII and COIII across different orders of reptiles. Estimation of overall base composition in the protein-coding sequences of COI, COII and COIII genes of the reptilian orders revealed an uneven usage of nucleotides. The overall count of A nucleotide was found to be the highest while the overall count of G nucleotide was the least. The CO genes across the three reptilian orders were prominently AT biased. Comparison of the GC proportion at each codon position displayed that GC1 percentage ranked the highest in all the three CO genes of the reptilian orders. SCUO values indicated weaker CUB, while considerable variation of SCUO values existed in the three CO genes across the studied reptiles. Relative synonymous codon usage (RSCU) values indicated that mostly the A ending codons were preferred. Based on the parameters namely neutrality plot, mutational responsive index and translational selection, we could conclude that natural selection was the major evolutionary force in COI, COII and COIII genes in the studied reptilian orders. However, correspondence analysis, parity plot and correlation studies indicated the existence of mutation pressure as well on the CO genes.

The complete mitochondrial genome of Ophiocordyceps gracilis and its comparison with related species

In this study, the complete mitochondrial genome of O. gracilis was sequenced and assembled before being compared with related species. As the second largest mitogenome reported in the family Ophiocordycipitaceae, the mitogenome of O. gracilis (voucher OG201301) is a circular DNA molecule of 134,288 bp that contains numerous introns and longer intergenomic regions. UCA was detected as anticodon in tRNA-Sec of O. gracilis, while comparative mitogenome analysis of nine Ophiocordycipitaceae fungi indicated that the order and contents of PCGs and rRNA genes were considerably conserved and could descend from a common ancestor in Ophiocordycipitaceae. In addition, the expansion of mitochondrial organization, introns, gene length, and order of O. gracilis were determined to be similar to those of O. sinensis, which indicated common mechanisms underlying adaptive evolution in O. gracilis and O. sinensis. Based on the mitochondrial gene dataset (15 PCGs and 2 RNA genes), a close genetic relationship between O. gracilis and O. sinensis was revealed through phylogenetic analysis. This study is the first to investigate the molecular evolution, phylogenetic pattern, and genetic structure characteristics of mitogenome in O. gracilis. Based on the obtained results, the mitogenome of O. gracilis can increase understanding of the genetic diversity and evolution of cordycipitoid fungi.

Genome-Wide Analysis of Codon Usage Patterns of SARS-CoV-2 Virus Reveals Global Heterogeneity of COVID-19

The ongoing outbreak of coronavirus disease COVID-19 is significantly implicated by global heterogeneity in the genome organization of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The causative agents of global heterogeneity in the whole genome of SARS-CoV-2 are not well characterized due to the lack of comparative study of a large enough sample size from around the globe to reduce the standard deviation to the acceptable margin of error. To better understand the SARS-CoV-2 genome architecture, we have performed a comprehensive analysis of codon usage bias of sixty (60) strains to get a snapshot of its global heterogeneity. Our study shows a relatively low codon usage bias in the SARS-CoV-2 viral genome globally, with nearly all the over-preferred codons' A.U. ended. We concluded that the SARS-CoV-2 genome is primarily shaped by mutation pressure; however, marginal selection pressure cannot be overlooked. Within the A/U rich virus genomes of SARS-CoV-2, the standard deviation in G.C. (42.91% ± 5.84%) and the GC3 value (30.14% ± 6.93%) points towards global heterogeneity of the virus. Several SARS-CoV-2 viral strains were originated from different viral lineages at the exact geographic location also supports this fact. Taking all together, these findings suggest that the general root ancestry of the global genomes are different with different genome's level adaptation to host. This research may provide new insights into the codon patterns, host adaptation, and global heterogeneity of SARS-CoV-2.

Insight into Codon Utilization Pattern of Tumor Suppressor Gene EPB41L3 from Different Mammalian Species Indicates Dominant Role of Selection Force

Simple Summary

The present study envisaged the codon usage pattern analysis of tumor suppressor gene EPB41L3 for the human, brown rat, domesticated cattle, and Sumatran orangutan. Most amino acids are coded by more than one synonymous codon, but they are used in a biased manner. The codon usage bias results from multiple factors like compositional properties, dinucleotide abundance, neutrality, parity, tRNA pool, etc. Understanding codon bias is central to fields as diverse as molecular evolution, gene expressivity, protein translation, and protein folding. This kind of studies is important to see the effects of various evolutionary forces on codon usage. The present study indicated that the selection force is dominant over other forces shaping codon usage in the envisaged organisms.

Abstract

Uneven codon usage within genes as well as among genomes is a usual phenomenon across organisms. It plays a significant role in the translational efficiency and evolution of a particular gene. EPB41L3 is a tumor suppressor protein-coding gene, and in the present study, the pattern of codon usage was envisaged. The full-length sequences of the EPB41L3 gene for the human, brown rat, domesticated cattle, and Sumatran orangutan available at the NCBI were retrieved and utilized to analyze CUB patterns across the selected mammalian species. Compositional properties, dinucleotide abundance, and parity analysis showed the dominance of A and G whilst RSCU analysis indicated the dominance of G/C-ending codons. The neutrality plot plotted between GC12 and GC3 to determine the variation between the mutation pressure and natural selection indicated the dominance of selection pressure (R = 0.926; p < 0.00001) over the three codon positions across the gene. The result is in concordance with the codon adaptation index analysis and the ENc-GC3 plot analysis, as well as the translational selection index (P2). Overall selection pressure is the dominant pressure acting during the evolution of the EPB41L3 gene.

Comparative Analysis of Mitochondrial Genome Features among Four Clonostachys Species and Insight into Their Systematic Positions in the Order Hypocreales

The mycoparasite fungi of Clonostachys have contributed to the biological control of plant fungal disease and nematodes. The Clonostachys fungi strains were isolated from Ophiocordyceps highlandensis, Ophiocordycepsnigrolla and soil, which identified as Clonostachyscompactiuscula, Clonostachysrogersoniana, Clonostachyssolani and Clonostachys sp. To explore the evolutionary relationship between the mentioned species, the mitochondrial genomes of four Clonostachys species were sequenced and assembled. The four mitogenomes consisted of complete circular DNA molecules, with the total sizes ranging from 27,410 bp to 42,075 bp. The GC contents, GC skews and AT skews of the mitogenomes varied considerably. Mitogenomic synteny analysis indicated that these mitogenomes underwent gene rearrangements. Among the 15 protein-coding genes within the mitogenomes, the nad4L gene exhibited the least genetic distance, demonstrating a high degree of conservation. The selection pressure analysis of these 15 PCGs were all below 1, indicating that PCGs were subject to purifying selection. Based on protein-coding gene calculation of the significantly supported topologies, the four Clonostachys species were divided into a group in the phylogenetic tree. The results supplemented the database of mitogenomes in Hypocreales order, which might be a useful research tool to conduct a phylogenetic analysis of Clonostachys. Additionally, the suitable molecular marker was significant to study phylogenetic relationships in the Bionectriaceae family.

The Insights of Genomic Synteny and Codon Usage Preference on Genera Demarcation of Iridoviridae Family

The members of the family Iridoviridae are large, double-stranded DNA viruses that infect various hosts, including both vertebrates and invertebrates. Although great progress has been made in genomic and phylogenetic analyses, the adequacy of the existing criteria for classification within the Iridoviridae family remains unknown. In this study, we redetermined 23 Iridoviridae core genes by re-annotation, core-pan analysis and local BLASTN search. The phylogenetic tree based on the 23 re-annotated core genes (Maximum Likelihood, ML-Tree) and amino acid sequences (composition vector, CV-Tree) were found to be consistent with previous reports. Furthermore, the information provided by synteny analysis and codon usage preference (relative synonymous codon usage, correspondence analysis, ENC-plot and Neutrality plot) also supports the phylogenetic relationship. Collectively, our results will be conducive to understanding the genera demarcation within the Iridoviridae family based on genomic synteny and component (codon usage preference) and contribute to the existing taxonomy methods for the Iridoviridae family.

Comparative mitochondrial genome analysis reveals intron dynamics and gene rearrangements in two Trametes species

Trametes species are efficient wood decomposers that are widespread throughout the world. Mitogenomes have been widely used to understand the phylogeny and evolution of fungi. Up to now, two mitogenomes from the Trametes genus have been revealed. In the present study, the complete mitogenomes of two novel Trametes species, Trametes versicolor and T. coccinea, were assembled and compared with other Polyporales mitogenomes. Both species contained circular DNA molecules, with sizes of 67,318 bp and 99,976 bp, respectively. Comparative mitogenomic analysis indicated that the gene number, length and base composition varied between the four Trametes mitogenomes we tested. In addition, all of the core protein coding genes in Trametes species were identified and subjected to purifying selection. The mitogenome of T. coccinea contained the largest number of introns among the four Trametes species tested, and introns were considered the main factors contributing to size variations of Polyporales. Several novel introns were detected in the Trametes species we assembled, and introns identified in Polyporales were found to undergo frequent loss/gain events. Large-scale gene rearrangements were detected between closely related Trametes species, including gene inversions, insertions, and migrations. A well-supported phylogenetic tree for 77 Basidiomycetes was obtained based on the combined mitochondrial gene set using 2 phylogenetic inference methods. The results showed that mitochondrial genes are effective molecular markers for understanding the phylogeny of Basidiomycetes. This study is the first to report the mitogenome rearrangement and intron dynamics of Trametes species, which shed light on the evolution of Trametes and other related species.

Understanding the codon usage patterns of mitochondrial CO genes among Amphibians

A universal phenomenon of using synonymous codons unequally in coding sequences known as codon usage bias (CUB) is observed in all forms of life. Mutation and natural selection drive CUB in many species but the relative role of evolutionary forces varies across species, genes and genomes. We studied the CUB in mitochondrial (mt) CO genes from three orders of Amphibia using bioinformatics approach as no work was reported yet. We observed that CUB of mt CO genes of Amphibians was weak across different orders. Order Caudata had higher CUB followed by Gymnophiona and Anura for all genes and CUB also varied across genes. Nucleotide composition analysis showed that CO genes were AT-rich. The AT content in Caudata was higher than that in Gymnophiona while Anura showed the least content. Multiple investigations namely nucleotide composition, correspondence analysis, parity plot analysis showed that the interplay of mutation pressure and natural selection caused CUB in these genes. Neutrality plot suggested the involvement of natural selection was more than the mutation pressure. The contribution of natural selection was higher in Anura than Gymnophiona and the lowest in Caudata. The codons CGA, TGA, AAA were found to be highly favoured by nature across all genes and orders.

Analysis of mitochondrial protein-coding genes of Antheraea assamensis: Muga silkworm of Assam

To understand the synonymous codon usage pattern in mitochondrial genome of Antheraea assamensis, we analyzed the 13 mitochondrial protein-coding genes of this species using a bioinformatic approach as no work was reported yet. The nucleotide composition analysis suggested that the percentages of A, T, G,and C were 33.73, 46.39, 9.7 and 10.17, respectively and the overall GC content was 19.86, that is, lower than 50% and the genes were AT rich. The mean effective number of codons of mitochondrial protein-coding genes was 36.30 and it indicated low codon usage bias (CUB). Relative synonymous codon usage analysis suggested overrepresented and underrepresented codons in each gene and the pattern of codon usage was different among genes. Neutrality plot analysis revealed a narrow range of distribution for GC content at the third codon position and some points were diagonally distributed, suggesting both mutation pressure and natural selection influenced the CUB.

Natural Selection Plays an Important Role in Shaping the Codon Usage of Structural Genes of the Viruses Belonging to the Coronaviridae Family

Viruses belonging to the Coronaviridae family have a single-stranded positive-sense RNA with a poly-A tail. The genome has a length of ~29.9 kbps, which encodes for genes that are essential for cell survival and replication. Different evolutionary constraints constantly influence the codon usage bias (CUB) of different genes. A virus optimizes its codon usage to fit the host environment on which it savors. This study is a comprehensive analysis of the CUB for the different genes encoded by viruses of the Coronaviridae family. Different methods including relative synonymous codon usage (RSCU), an Effective number of codons (ENc), parity plot 2, and Neutrality plot, were adopted to analyze the factors responsible for the genetic evolution of the Coronaviridae family. Base composition and RSCU analyses demonstrated the presence of A-ended and U-ended codons being preferred in the 3rd codon position and are suggestive of mutational selection. The lesser ENc value for the spike ‘S’ gene suggests a higher bias in the codon usage of this gene compared to the other structural genes. Parity plot 2 and neutrality plot analyses demonstrate the role and the extent of mutational and natural selection towards the codon usage pattern. It was observed that the structural genes of the Coronaviridae family analyzed in this study were at the least under 84% influence of natural selection, implying a major role of natural selection in shaping the codon usage.

The 287,403 bp Mitochondrial Genome of Ectomycorrhizal Fungus Tuber calosporum Reveals Intron Expansion, tRNA Loss, and Gene Rearrangement

In the present study, the mitogenome of Tuber calosporum was assembled and analyzed. The mitogenome of T. calosporum comprises 15 conserved protein-coding genes, two rRNA genes, and 14 tRNAs, with a total size of 287,403 bp. Fifty-eight introns with 170 intronic open reading frames were detected in the T. calosporum mitogenome. The intronic region occupied 69.41% of the T. calosporum mitogenome, which contributed to the T. calosporum mitogenome significantly expand relative to most fungal species. Comparative mitogenomic analysis revealed large-scale gene rearrangements occurred in the mitogenome of T. calosporum, involving gene relocations and position exchanges. The mitogenome of T. calosporum was found to have lost several tRNA genes encoding for cysteine, aspartate, histidine, etc. In addition, a pair of fragments with a total length of 32.91 kb in both the nuclear and mitochondrial genomes of T. calosporum was detected, indicating possible gene transfer events. A total of 12.83% intragenomic duplications were detected in the T. calosporum mitogenome. Phylogenetic analysis based on mitochondrial gene datasets obtained well-supported tree topologies, indicating that mitochondrial genes could be reliable molecular markers for phylogenetic analyses of Ascomycota. This study served as the first report on mitogenome in the family Tuberaceae, thereby laying the groundwork for our understanding of the evolution, phylogeny, and population genetics of these important ectomycorrhizal fungi.

Mitogenomes of Two Phallus Mushroom Species Reveal Gene Rearrangement, Intron Dynamics, and Basidiomycete Phylogeny

Phallus indusiatus and Phallus echinovolvatus are edible bamboo mushrooms with pharmacological properties. We sequenced, assembled, annotated, and compared the mitogenomes of these species. Both mitogenomes were composed of circular DNA molecules, with sizes of 89,139 and 50,098 bp, respectively. Introns were the most important factor in mitogenome size variation within the genus Phallus. Phallus indusiatus, P. echinovolvatus, and Turbinellus floccosus in the subclass Phallomycetidae have conservative gene arrangements. Large-scale gene rearrangements were observed in species representing 42 different genera of Basidiomycetes. A variety of intron position classes were found in the 44 Basidiomycete species analyzed. A novel group II intron from the P. indusiatus mitogenome was compared with other fungus species containing the same intron, and we demonstrated that the insertion sites of the intron had a base preference. Phylogenetic analyses based on combined gene datasets yielded well-supported Bayesian posterior probability (BPP = 1) topologies. This indicated that mitochondrial genes are reliable molecular markers for analyzing the phylogenetic relationships of the Basidiomycetes. This is the first study of the mitogenome of the genus Phallus, and it increases our understanding of the population genetics and evolution of bamboo mushrooms and related species.

The 256 kb mitochondrial genome of Clavaria fumosa is the largest among phylum Basidiomycota and is rich in introns and intronic ORFs

In the present study, the complete mitogenome of Clavaria fumosa, was sequenced, assembled, and compared. The complete mitogenome of C. fumosa is 256,807 bp in length and is the largest mitogenomes among all Basidiomycota mitogenomes reported. Comparative mitogenomic analysis indicated that the C. fumosa mitogenome contained the most introns and intronic ORFs among all fungal mitogenomes. Large intergenic regions, intronic regions, accumulation of repeat sequences and plasmid-derived genes together promoted the size expansion of the C. fumosa mitogenome. In addition, the rps3 gene was found subjected to positive selection between some Agaricales species. We found frequent intron gain/loss events in Agaricales mitogenomes, and four novel intron classes were detected in the C. fumosa mitogenome. Large-scale gene rearrangements were found occurred in Agaricales species and the C. fumosa mitogenome had a unique gene arrangement which differed from other Agaricales species. Phylogenetic analysis for 76 Basidiomycetes based on combined mitochondrial gene sets indicated that mitochondrial genes could be used as effective molecular markers for reconstructing evolution of Basidiomycota. The study served as the first report on the mitogenomes of the family Clavariaceae, which will promote the understanding of the genetics, evolution and taxonomy of C. fumosa and related species.

Codon usage pattern and evolutionary forces of mitochondrial ND genes among orders of class Amphibia

In this study, we used a bioinformatics approach to analyze the nucleotide composition and pattern of synonymous codon usage in mitochondrial ND genes in three amphibian groups, that is, orders Anura, Caudata, and Gymnophiona to identify the commonality and the differences of codon usage as no research work was reported yet. The high value of the effective number of codons revealed that the codon usage bias (CUB) was low in mitochondrial ND genes among the orders. Nucleotide composition analysis suggested that for each gene, the compositional features differed among Anura, Caudata, and Gymnophiona and the GC content was lower than AT content. Furthermore, a highly significant difference (p < .05) for GC content was found in each gene among the orders. The heat map showed contrasting patterns of codon usage among different ND genes. The regression of GC12 on GC3 suggested a narrow range of GC3 distribution and some points were located in the diagonal, indicating both mutation pressure and natural selection might influence the CUB. Moreover, the slope of the regression line was less than 0.5 in all ND genes among orders, indicating natural selection might have played the dominant role whereas mutation pressure had played a minor role in shaping CUB of ND genes across orders.

Insights into The Codon Usage Bias of 13 Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Isolates from Different Geo-locations

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the causative agent of Coronavirus disease 2019 (COVID-19) which is an infectious disease that spread throughout the world and was declared as a pandemic by the World Health Organization (WHO). In this study, we performed a genome-wide analysis on the codon usage bias (CUB) of 13 SARS-CoV-2 isolates from different geo-locations (countries) in an attempt to characterize it, unravel the main force shaping its pattern, and understand its adaptation to Homo sapiens . Overall results revealed that, SARS-CoV-2 codon usage is slightly biased similarly to other RNA viruses. Nucleotide and dinucleotide compositions displayed a bias toward A/U content in all codon positions and CpU-ended codons preference, respectively. Eight common putative preferred codons were identified, and all of them were A/U-ended (U-ended: 7, A-ended: 1). In addition, natural selection was found to be the main force structuring the codon usage pattern of SARS-CoV-2. However, mutation pressure and other factors such as compositional constraints and hydrophobicity had an undeniable contribution. Two adaptation indices were utilized and indicated that SARS-CoV-2 is moderately adapted to Homo sapiens compared to other human viruses. The outcome of this study may help in understanding the underlying factors involved in the evolution of SARS-CoV-2 and may aid in vaccine design strategies.

Codon usage pattern and its influencing factors for mitochondrial CO genes among different classes of Arthropoda

Analysis of codon usage bias (CUB) is very much important in perceiving the knowledge of molecular biology, the discovery of a new gene, designing of transgenes and evolution of gene. In this study, we analyzed compositional features and codon usage of MT-CO (COI, COII and COIII) genes among the classes of Arthropoda to explore the pattern of CUB as no research work was reported yet. Nucleotide composition analysis in CO genes suggested that the genes were AT-rich in all the four classes of Arthropoda. CUB was low in all the classes of Arthropoda for MT-CO genes as revealed from a high effective number of codons (ENC). We also found that the evolutionary forces namely mutation pressure and natural selection were the key influencing factors in CUB among MT-CO genes as revealed by correlation analysis between overall nucleotide composition and nucleotide composition at the 3rd codon position. Correspondence analysis suggested that the pattern of CUB was different among the classes of Arthropoda. Further, it was revealed from the neutrality plot that natural selection had a dominant role while mutation pressure exhibited a minor role in structuring the pattern of codon usage in all the classes of Arthropoda across COI, COII and COIII genes.

Comparative Mitogenome Analysis Reveals Mitochondrial Genome Differentiation in Ectomycorrhizal and Asymbiotic Amanita Species

In this present study, we assembled and analyzed the mitogenomes of two asymbiotic and six ectomycorrhizal Amanita species based on next-generation sequencing data. The size of the eight Amanita mitogenomes ranged from 37,341 to 137,428 bp, and we considered introns to be one of the main factors contributing to the size variation of Amanita. The introns of the cox1 gene experienced frequent gain/loss events in Amanita; and the intron position class cox1P386 was lost in the six ectomycorrhizal Amanita species. In addition, ectomycorrhizal Amanita species had more repetitive sequences and fewer intergenic sequences than asymbiotic Amanita species in their mitogenomes. Large-scale gene rearrangements were detected in the Amanita species we tested, including gene displacements and inversions. On the basis of the combined mitochondrial gene set, we reconstructed the phylogenetic relationships of 66 Basidiomycetes. The six ectomycorrhizal Amanita species were of single origin, and the two saprophytic Amanita species formed two distinct clades. This study is the first to elucidate the functions of the mitogenome in the evolution and ecological adaptation of Amanita species.

Codon Usage Bias Analysis of Bluetongue Virus Causing Livestock Infection

Bluetongue virus (BTV) is a double-stranded RNA virus with multiple segments and belongs to the genus Orbivirus within the family Reoviridae. BTV is spread to livestock through its dominant vector, biting midges of genus Culicoides. Although great progress has been made in genomic analyses, it is not fully understood how BTVs adapt to their hosts and evade the host's immune systems. In this study, we retrieved BTV genome sequences from the National Center for Biotechnology Information (NCBI) database and performed a comprehensive research to explore the codon usage patterns in 50 BTV strains. We used bioinformatic approaches to calculate the relative synonymous codon usage (RSCU), codon adaptation index (CAI), effective number of codons (ENC), and other indices. The results indicated that most of the overpreferred codons had A-endings, which revealed that mutational pressure was the major force shaping codon usage patterns in BTV. However, the influence of natural selection and geographical factors cannot be ignored on viral codon usage bias. Based on the RSCU values, we performed a comparative analysis between BTVs and their hosts, suggesting that BTVs were inclined to evolve their codon usage patterns that were comparable to those of their hosts. Such findings will be conducive to understanding the elements that contribute to viral evolution and adaptation to hosts.

Comparative Analyses of Mitochondrial Genomes Provide Evolutionary Insights Into Nematode-Trapping Fungi

Predatory fungi in Orbiliaceae (Ascomycota) have evolved a diversity of trapping devices that enable them to trap and kill nematodes, other small animals, and protozoans. These trapping devices include adhesive hyphae, adhesive knobs, adhesive networks, constricting rings, and non-constricting rings. Their diversity and practical importance have attracted significant attention from biologists, making them excellent model organisms for studying adaptative evolution and as biological control agents against parasitic nematodes. The putative origins and evolutionary relationships among these carnivorous fungi have been investigated using nuclear protein-encoding genes, but their patterns of mitogenome relationships and divergences remain unknown. Here we analyze and compare the mitogenomes of 12 fungal strains belonging to eight species, including six species representing all four types of nematode trapping devices and two from related but non-predatory fungi. All 12 analyzed mitogenomes were of circular DNA molecules, with lengths ranging from 146,101 bp to 280,699 bp. Gene synteny analysis revealed several gene rearrangements and intron transfers among the mitogenomes. In addition, the number of protein coding genes (PCGs), GC content, AT skew, and GC skew varied among these mitogenomes. The increased number and total size of introns were the main contributors to the length differences among the mitogenomes. Phylogenetic analyses of the protein-coding genes indicated that mitochondrial and nuclear genomes evolved at different rates, and signals of positive selection were found in several genes involved in energy metabolism. Our study provides novel insights into the evolution of nematode-trapping fungi and shall facilitate further investigations of this ecologically and agriculturally important group of fungi.

Characterization of the mitochondrial genome of the pathogenic fungus Scytalidium auriculariicola (Leotiomycetes) and insights into its phylogenetics

Scytalidium auriculariicola is the causative pathogen of slippery scar disease in the cultivated cloud ear fungus, Auricularia polytricha. In the present study, the mitogenome of S. auriculariicola was sequenced and assembled by next-generation sequencing technology. The circular mitogenome is 96,857 bp long and contains 56 protein-coding genes, 2 ribosomal RNA genes, and 30 transfer RNA genes (tRNAs). The high frequency of A and T used in codons contributed to the high AT content (73.70%) of the S. auriculariicola mitogenome. Comparative analysis indicated that the base composition and the number of introns and protein-coding genes in the S. auriculariicola mitogenome varied from that of other Leotiomycetes mitogenomes, including a uniquely positive AT skew. Five distinct groups were found in the gene arrangements of Leotiomycetes. Phylogenetic analyses based on combined gene datasets (15 protein-coding genes) yielded well-supported (BPP = 1) topologies. A single-gene phylogenetic tree indicated that the nad4 gene may be useful as a molecular marker to analyze the phylogenetic relationships of Leotiomycetes species. This study is the first report on the mitochondrial genome of the genus Scytalidium, and it will contribute to our understanding of the population genetics and evolution of S. auriculariicola and related species.

Insights into the nucleotide composition and codon usage pattern of human tumor suppressor genes

Tumor suppressor genes encode different proteins that inhibit the uncontrolled proliferation of cell growth and tumor development. To acquire clues for predicting gene expression level, it is essential to understand the codon usage bias (CUB) of genes to characterize genome which possesses its own compositional characteristics and unique coding sequences. We used bioinformatic tools to analyze the codon usage patterns of 637 human tumor suppressor genes as no work was reported earlier. The mean effective number of codons of these genes was 48, indicating low CUB. Our results exhibited a significant positive correlation among different nucleotide compositions and the codons ending with C base was most frequently used along with the most over-represented codon CTG and GTG codifying leucine and valine amino acid, respectively, in human tumor suppressor genes. The neutrality plot showed a significant positive correlation (Pearson, r = 0. 646; P < .01) suggesting that mutation on GC bias might affect the CUB. However, the linear regression coefficient of GC₁₂ on GC₃ in human tumor suppressor genes suggested that natural selection played a major role while mutation pressure played a minor role in the codon usage patterns of tumor suppressor genes in human. Our study would throw light into the factors that affect CUB and the codon usage patterns in the human tumor suppressor genes.

Comparative mitogenomics of the Decapoda reveals evolutionary heterogeneity in architecture and composition

The emergence of cost-effective and rapid sequencing approaches has resulted in an exponential rise in the number of mitogenomes on public databases in recent years, providing greater opportunity for undertaking large-scale comparative genomic and systematic research. Nonetheless, current datasets predominately come from small and disconnected studies on a limited number of related species, introducing sampling biases and impeding research of broad taxonomic relevance. This study contributes 21 crustacean mitogenomes from several under-represented decapod infraorders including Polychelida and Stenopodidea, which are used in combination with 225 mitogenomes available on NCBI to investigate decapod mitogenome diversity and phylogeny. An overview of mitochondrial gene orders (MGOs) reveals a high level of genomic variability within the Decapoda, with a large number of MGOs deviating from the ancestral arthropod ground pattern and unevenly distributed among infraorders. Despite the substantial morphological and ecological variation among decapods, there was limited evidence for correlations between gene rearrangement events and species ecology or lineage specific nucleotide substitution rates. Within a phylogenetic context, predicted scenarios of rearrangements show some MGOs to be informative synapomorphies for some taxonomic groups providing strong independent support for phylogenetic relationships. Additional comparisons for a range of mitogenomic features including nucleotide composition, strand asymmetry, unassigned regions and codon usage indicate several clade-specific trends that are of evolutionary and ecological interest.

Compositional properties and codon usage pattern of mitochondrial ATP gene in different classes of Arthropoda

Codon usage bias (CUB) is defined as the usage of synonymous codons unequally for an amino acid in a gene transcript. It is influenced by both mutation pressure and natural selection and is a species-specific property. In our current study, we used bioinformatic methods to investigate the coding sequences of mitochondrial adenosine triphosphate gene (MT-ATP) in different classes of arthropoda to know the codon usage pattern of the gene as no work was described earlier. The analysis of compositional properties suggested that the gene is AT rich. The effective number of codons revealed the CUB of both ATP6 and ATP8 gene was moderate. Heat map showed that the codons ending with AT were negatively associated with GC3 while the codons ending with GC were positively associated with GC3 in all the classes of arthropoda. Correspondence study revealed that the pattern of codon usage of ATP6 and ATP8 genes differed across classes. Neutrality plot suggested the codon usage bias of these two genes in phylum arthropoda was influenced by both mutation pressure and natural selection.

Analysis of Nipah Virus Codon Usage and Adaptation to Hosts

A recent outbreak of Nipah virus (NiV) in India has caused 17 deaths in people living in districts of Kerala state. Its zoonotic nature, as well as high rate of human-to-human transmission, has led researchers worldwide to work toward understanding the different aspects of the NiV. We performed a codon usage analysis, based on publicly available nucleotide sequences of NiV and its host adaptation, along with other members of the Henipavirus genus in ten hosts. NiV genome encodes nine open reading frames; and overall, no significant bias in codon usage was observed. Aromaticity of proteins had no impact on codon usage. An analysis of preferred codons used by NiV and the tRNA pool in human cells indicated that NiV prefers codons from a suboptimal anticodon tRNA pool. We observed that codon usage by NiV is mainly constrained by compositional and selection pressures, not by mutational forces. Parameters that define NiV and host relatedness in terms of codon usage were analyzed, with a codon adaptation index (CAI), relative codon deoptimization index (RCDI), and similarity index calculations; which indicated that, of all hosts analyzed, NiV was best adapted to African green monkeys. A comparative analysis based on the relative codon deoptimization index (RCDI) for host adaptation of NiV, Hendra virus (HeV), Cedar virus (CedV), and Hendra like Mojiang virus (MojV) revealed that except for dogs and ferrets, all evaluated hosts were more susceptible to HeV than NiV.

Insights into the genetic and host adaptability of emerging porcine circovirus 3

Porcine circovirus 3 (PCV3) was found to be associated with reproductive disease in pigs, and since its first identification in the United States, it subsequently spread worldwide, especially in China, where it might pose a potential threat to the porcine industry. However, no exhaustive analysis was performed to understand its evolution in the prospect of codon usage pattern. Here, we performed a deep codon usage analysis of PCV3. PCV3 sequences were classified into two clades: PCV3a and PCV3b, confirmed by principal component analysis. Additionally, the degree of codon usage bias of PCV3 was slightly low as inferred from the analysis of the effective number of codons. The codon usage pattern was mainly affected by natural selection, but there was a co-effect of mutation pressure and dinucleotide frequency. Moreover, based on similarity index analysis, codon adaptation index analysis and relative codon deoptimization index analysis, we found that PCV3 might pose a potential risk to public health though with unknow pathogenicity. In conclusion, this work reinforces the systematic understanding of the evolution of PCV3, which was reflected by the codon usage patterns and fitness of this novel emergent virus.

The codon usage pattern of genes involved in ovarian cancer

In this study, we analyzed the compositional dynamics and codon usage pattern of genes involved in ovarian cancer (OC) using a computational method. Mutations in specific genes are associated with OC, and some genes are risk factors for progression of OC, but no work has been reported yet on the codon usage pattern of genes involved in OC. Nucleotide composition analysis of OC-related genes suggested that the overall GC content was higher than AT content; that is, the genes were GC rich. The improved effective number of codons indicated that the overall extent of codon usage bias of genes involved in OC was low. The codons AGC, CTG, ATC, ACC, GTG, and GCC were overrepresented, while the codons TCG, TTA, CTA, CCG, CAA, CGT, ATA, ACG, GTA, GTT, GCG, and GGT were underrepresented in the genes. Correspondence analysis suggested that the codon usage pattern was different in different genes. A highly significant correlation was observed between GC12 and GC3 (r = 0.587, P < 0.01) of genes, suggesting that directional mutation affected the three codon positions. Our report on the codon usage pattern of genes involved in OC includes a new perspective for elucidating the mechanisms of biased usage of synonymous codons, as well as providing useful clues for molecular genetic engineering.

A cross-talk on compositional dynamics and codon usage patterns of mitochondrial CYB gene in Echinodermata

Codon usage bias (CUB) refers to a phenomenon in which some synonymous codons are used in mature mRNA at a higher frequency than other members codifying the same amino acid. CUB is mainly determined by mutation pressure and natural selection. We used bioinformatic tools to analyze the protein coding sequences of mitochondrial CYB gene in different classes of Echinodermata to understand the patterns of codon usage. The ENC values of CYB gene in five different classes of Echinodermata were 41.64, 30.33, 43.63, 41.11, and 41.33, which suggested that the CUB of this gene was low. The relative synonymous codon usage (RSCU) values showed that the patterns of over-represented and under-represented codons were different among different classes. Correspondence analysis indicated that the plots of CYB gene were different across classes, suggesting that the pattern of codon usage was also different among five classes under study. Highly significant correlation (p < .01) between overall nucleotide composition and its 3rd codon position indicated that both mutational pressure and natural selection had an influence on the codon usage bias of CYB gene. Furthermore, PR-2 bias plot analysis showed that both mutation pressure and natural selection might have affected the pattern of codon usage in CYB gene of Echinodermata.

Genetic and evolutionary analysis of emerging H3N2 canine influenza virus

The H3N2 canine influenza virus (CIV) originated from an avian species. Since its emergence, it has circulated in multiple states and has caused pandemics among dog populations; however, no comprehensive studies have explored the causes driving these ongoing cases. The study of the codon usage patterns of viruses can reveal the genetic changes required for the viruses to adapt to new hosts and the external environment. Here we performed a thorough genetic, evolutionary, and codon usage analysis. We identified three evolutionary H3N2 CIV clades from a timescaled phylogenetic tree, namely, Origin, China, and Korea/USA, by principal component analysis (PCA). Additionally, we found a low codon usage bias and that mutation pressure, natural selection, and dinucleotide abundance shape the codon usage bias of H3N2 CIVs, with natural selection being more crucial than the others. Moreover, the human codon adaptation index was similar to that of dogs (the natural host) and cats. In addition, the H3N2 CIV similarity index values were higher than those of the avian influenza virus (AIV), suggesting viral adaptation to the host. Therefore, H3N2 CIVs may pose a potential risk to public health in the future, and further epidemiologic, evolutionary, and pathogenetic studies are required.

Compositional bias coupled with selection and mutation pressure drives codon usage in Brassica campestris genes

The plant Brassica campestris includes the vegetables turnip and Chinese cabbage, important plants of economic importance. Here, we have analysed the codon usage bias of B. campestris for 116 protein coding genes. Neutrality analysis showed that B. campestris had a wide range of GC3s, and a significant correlation was observed between GC12 and GC3. Nc versus GC3s plot showed a few genes on or proximate to the expected curve, but the majority of points were found to be scattered distantly from the expected curve. Correspondence analysis on codon usage revealed that the position preference of codons on multidimensional space totally depends on the presence of A and T at synonymous third codon position. These results altogether suggest that composition bias along with selection (major) and mutation pressure (minor) affects the codon usage pattern of the protein coding genes in Brassica campestris.

Genetic and codon usage bias analyses of polymerase genes of equine influenza virus and its relation to evolution

BACKGROUND

Equine influenza is a major health problem of equines worldwide. The polymerase genes of influenza virus have key roles in virus replication, transcription, transmission between hosts and pathogenesis. Hence, the comprehensive genetic and codon usage bias of polymerase genes of equine influenza virus (EIV) were analyzed to elucidate the genetic and evolutionary relationships in a novel perspective.

RESULTS

The group - specific consensus amino acid substitutions were identified in all polymerase genes of EIVs that led to divergence of EIVs into various clades. The consistent amino acid changes were also detected in the Florida clade 2 EIVs circulating in Europe and Asia since 2007. To study the codon usage patterns, a total of 281,324 codons of polymerase genes of EIV H3N8 isolates from 1963 to 2015 were systemically analyzed. The polymerase genes of EIVs exhibit a weak codon usage bias. The ENc-GC3s and Neutrality plots indicated that natural selection is the major influencing factor of codon usage bias, and that the impact of mutation pressure is comparatively minor. The methods for estimating host imposed translation pressure suggested that the polymerase acidic (PA) gene seems to be under less translational pressure compared to polymerase basic 1 (PB1) and polymerase basic 2 (PB2) genes. The multivariate statistical analysis of polymerase genes divided EIVs into four evolutionary diverged clusters - Pre-divergent, Eurasian, Florida sub-lineage 1 and 2.

CONCLUSIONS

Various lineage specific amino acid substitutions observed in all polymerase genes of EIVs and especially, clade 2 EIVs underwent major variations which led to the emergence of a phylogenetically distinct group of EIVs originating from Richmond/1/07. The codon usage bias was low in all the polymerase genes of EIVs that was influenced by the multiple factors such as the nucleotide compositions, mutation pressure, aromaticity and hydropathicity. However, natural selection was the major influencing factor in defining the codon usage patterns and evolution of polymerase genes of EIVs.

Nucleotide composition determines the role of translational efficiency in human genes

The basic sequence features were analysed that influence gene expression via codon usage bias of the selected forty coding sequences of Homo sapiens in a simple prokaryotic model i.e. E. coli K-12 genome. The prime objective was to elucidate the interrelationships among tRNA gene copy numbers, synonymous codons, amino acids and translational efficiency using tRNA adaptation index. It was evident from RSCU scores and principal component analysis, that only those preferred codons were used by the isoacceptor tRNAs that had G and C base at their third codon position. Relationship between tRNA adaptation index and amino acids, revealed that valine, arginine, serine and isoleucine showed significant positive correlation with gene expression. Therefore, it could be inferred that GC content in these genes might have the major role in shaping the codon bias and affecting the translational efficiency of the coding sequences.

Nucleotide composition and codon usage bias of SRY gene

The SRY gene is present within the sex-determining region of the Y chromosome which is responsible for maleness in mammals. The nonuniform usage of synonymous codons in the mRNA transcript for encoding a particular amino acid is the codon usage bias (CUB). Analysis of codon usage pattern is important to understand the genetic and molecular organisation of a gene. It also helps in heterologous gene expression, design of primer and synthetic gene. However, the analysis of codon usage bias of SRY gene was not yet studied. We have used bioinformatic tools to analyse codon usage bias of SRY gene across mammals. Codon bias index (CBI) indicated that the overall extent of codon usage bias was weak. The relative synonymous codon usage (RSCU) analysis suggested that most frequently used codons had an A or C at the third codon position. Compositional constraint played an important role in codon usage pattern as evident from correspondence analysis (CA). Significant correlation among nucleotides constraints indicated that both mutation pressure and natural selection affect the codon usage pattern. Neutrality plot suggested that natural selection might play a major role, while mutation pressure might play a minor role in codon usage pattern in SRY gene in different species of mammals.

Codon usage pattern and prediction of gene expression level in Bungarus species

Codon bias study in an organism gains significance in understanding the molecular mechanism as well as the functional conservation of gene expression during the course of evolution. The prime focus in this study is to compare the codon usage patterns among the four species belonging to the genus Bungarus (B. multicinctus, B. fasciatus, B. candidus and B. flaviceps) using several codon bias parameters. Our results suggested that relatively low codon bias exists in the coding sequences of the selected species. The compositional constraints together with gene expression level might influence the patterns of codon usage among the genes of Bungarus species. Both natural selection and mutation pressure affect the codon usage pattern in Bungarus species as evident from correspondence analysis. Neutrality plot indicates that natural selection played a major role while mutation pressure played a minor role in codon usage pattern of the genes in Bungarus species.