Optimal Codons Research Articles

Analysis of synonymous codon usage of transcriptome database in Rheum palmatum.

Background Rheum palmatum is an endangered and important medicinal plant in Asian countries, especially in China. However, there is little knowledge about the codon usage bias for R. palmatum CDSs. In this project, codon usage bias was determined based on the R. palmatum 2,626 predicted CDSs from R. palmatum transcriptome.MethodsIn this study, all codon usage bias parameters and nucleotide compositions were calculated by Python script, Codon W, DNA Star, CUSP of EMBOSS.ResultsThe average GC and GC3 content are 46.57% and 46.6%, respectively, the results suggested that there exists a little more AT than GC in the R. palmatum genes, and the codon bias of R. palmatum genes preferred to end with A/T. We concluded that the codon bias in R. palmatum was affect by nucleotide composition, mutation pressure, natural selection, gene expression levels, and the mutation pressure is the prominent factor. In addition, we figured out 28 optimal codons and most of them ended with A or U. The project here can offer important information for further studies on enhancing the gene expression using codon optimization in heterogeneous expression system, predicting the genetic and evolutionary mechanisms in R. palmatum.

Analysis of Codon Usage Bias in the <i>Platycarya</i> Chloroplast Genome

To detect the codon usage characteristics of chloroplast genomes in  Platycarya  genus, the CodonW 、 CUSP and SPSSAU software were employed to analyze the codon usage patterns of the chloroplast genomes protein-coding sequence in  Platycarya longipes  and  Platycarya strobilacea   in this research. Results show that the GC content of chloroplast genomes was 37.75% and 37.80%, the average GC content in the 3rd position was 27.16% and 27.25%. the range of effective codon number from 35.19 to 56.98, and there were more than 2/3 genes when ENC value greater than 45, which indicated a weak preference. According to the results of neutrality plot analysis, ENC-plot analysis and PR2-plot analysis, codon bias in most  Platycarya  chloroplast genes were affected by natural selection, while a few were affected by mutations or other factors. And based on the ENC value, five groups of high-expressed and low-expressed genes were identified, 16 codons were ended with A/U among the 18 optimal codons. The research has implications on codon optimization, enhancing the expression efficiency of exogenous gene and phylogenetic analysis.

Complete chloroplast genome sequences and codon usage pattern among three wetland plants

AbstractArtificial wetlands are now constructed to be used for wastewater treatment, water quality improvement of reservoirs, and landscape reintegration purposes. The removal and degradation of enriched nutrients and pollutants from them are efficiently done by the activity of wetland plants. Most studies are focused on the purification capacity; the identification and classification of these species are lacking. In the present research, chloroplast genomes (cp genome) of three wetland plants namely, Cyperus alternifolius L., Thalia dealbata Fraser, and Canna indica L. were examined. The cp genomes of these species were sampled and sequenced using Illumina HiSeq platform with a 300‐bp paired‐end sequencing followed by the analysis of codon usage pattern. In the experiment, 3.86 Gb clean data were obtained and 310 genes from each of C. alternifolius and T. dealbata and 62 genes in C. indica were predicted. In the optimal codons analysis, showed that three cp genome preferred A/U‐ending and 3, 11, and 14 were identified in the C. alternifolius, T. dealbata, and C. indica cp genomes, respectively. Advanced analysis indicated that other factors (e.g., natural selection) play a major role in shaping codon usage pattern rather than mutation pressure. These results extend the codon usage bias study of plants and provide genetic data for further identification and phylogenetic studies.

English

Dengue viruses (DENV) are the most common mosquito-borne RNA virus with high variation and adaptation in tropical and subtropical regions. Exploration of codon usage bias of DENV can be significant to understand their genetic variation and adaptation. In the study, the codon usage pattern of dengue virus type 1 (DENV-1) was analyzed by using codonW, CUSP and SPSS. The extent of codon preference of DENV-1 is weak with a 50.57 mean value of ENC, indicating that the DENV-1 genome has low codon bias. Of the 18 optimal codons of DENV-1, 13 end in A/U, with A ending in the majority. The result shows that DENV-1 prefers A-ended codons, and their codon bias is influenced more by natural selection than by mutations selection, as revealed by ENC-plot and neutrality analysis. Furthermore, comparison of codon usage bias between DENV-1 and host showed that codon usage pattern of DENV-1 is more similar to Home sapiens instead of Aedes aegypti or A. albopictus. Our findings contributed to understanding of the evolution of the DENV-1.   Key words: Dengue virus type 1, Codon bias, RSCU, ENC-plot, neutrality-plot.

FMRP links optimal codons to mRNA stability in neurons

Fragile X syndrome (FXS) is caused by inactivation of the FMR1 gene and loss of encoded FMRP, an RNA binding protein that represses translation of some of its target transcripts. Here we use ribosome profiling and RNA sequencing to investigate the dysregulation of translation in the mouse brain cortex. We find that most changes in ribosome occupancy on hundreds of mRNAs are largely driven by dysregulation in transcript abundance. Many down-regulated mRNAs, which are mostly responsible for neuronal and synaptic functions, are highly enriched for FMRP binding targets. RNA metabolic labeling demonstrates that, in FMRP-deficient cortical neurons, mRNA down-regulation is caused by elevated degradation and is correlated with codon optimality. Moreover, FMRP preferentially binds mRNAs with optimal codons, suggesting that it stabilizes such transcripts through direct interactions via the translational machinery. Finally, we show that the paradigm of genetic rescue of FXS-like phenotypes in FMRP-deficient mice by deletion of the Cpeb1 gene is mediated by restoration of steady-state RNA levels and consequent rebalancing of translational homeostasis. Our data establish an essential role of FMRP in codon optimality-dependent mRNA stability as an important factor in FXS.

Analysis of codon usage bias and evolution in the chloroplast genome of Mesona chinensis Benth.

Mesona chinensis Benth (MCB) is one of the main economic crops in tropical and subtropical areas. To understand the codon usage bias (CUB) in M. chinensis Benth, chloroplast genome is essential to study its genetic law, molecular phylogenetic relationships, and exogenous gene expression. Results showed that the GC content of 53 CDS sequences was 37.95%, and GC1, GC2, and GC3 content were 46.02%, 38.26%, and 29.85%, respectively. The general GC content order was GC1>GC2>GC3. Moreover, the majority of genes had an effective number of codon (ENC) value greater than 40, except ndhE, rps8, and rps18. Correlation analysis results revealed that the GC content was significantly correlated with GC1, GC2, GC3, and ENC. Neutrality plot analysis, ENC-plot analysis, and PR2-plot analysis presented that the CUB of M. chinensis Benth chloroplast genome was mainly affected by mutation and selection. In addition, GGG, GCA, and TCC were found to be the optimal codons. Furthermore, results of cluster analysis and evolutionary tree showed that M. chinensis Benth was closely related to Ocimum basilicum, indicating that there was a certain correlation between the CUB of the chloroplast gene and the genetic relationship of plant species. Overall, the study on the CUB of chloroplast genome laid a basis for genetic modification and phylogenetic research of M. chinensis Benth chloroplast genome.

Analysis of codon usage bias reveals optimal codons in Elaeis guineensis

Abstract. Aditama R, Tanjung ZA, Sudania WM, Nugroho YA, Utomo C, Liwang T. 2020. Analysis of codon usage bias reveals optimal codons in Elaeis guineensis. Biodiversitas 21: 5331-5337. Codon usage bias of oil palm genome was reported employing several indices, including GC content, relative synonymous codon usage (RSCU), the effective number of codons (ENC), and codon adaptation index (CAI). Unimodal distribution of GC content was observed and matched with non-grass monocots characteristics. Correspondence analysis (COA) on synonymous codon usage bias showed that the main axis was strongly driven by GC content. The ENC and neutrality plot of oil palm genes indicating that natural selection played more vital role compared to mutational bias on shaping codon usage bias. A positive correlation between calculated CAI and experimental data of oil palm gene expression was detected indicating good ability of this index. Finally, eighteen codons were defined as “optimal codons” that may provide a useful reference for heterogeneous expression and genome editing studies.

Demographic history and adaptive synonymous and nonsynonymous variants of nuclear genes in Rhododendron oldhamii (Ericaceae)

Demographic events are important in shaping the population genetic structure and exon variation can play roles in adaptive divergence. Twelve nuclear genes were used to investigate the species-level phylogeography of Rhododendron oldhamii, test the difference in the average GC content of coding sites and of third codon positions with that of surrounding non-coding regions, and test exon variants associated with environmental variables. Spatial expansion was suggested by R2 index of the aligned intron sequences of all genes of the regional samples and sum of squared deviations statistic of the aligned intron sequences of all genes individually and of all genes of the regional and pooled samples. The level of genetic differentiation was significantly different between regional samples. Significantly lower and higher average GC contents across 94 sequences of the 12 genes at third codon positions of coding sequences than that of surrounding non-coding regions were found. We found seven exon variants associated strongly with environmental variables. Our results demonstrated spatial expansion of R. oldhamii in the late Pleistocene and the optimal third codon position could end in A or T rather than G or C as frequent alleles and could have been important for adaptive divergence in R. oldhamii.

Design principles of gene evolution for niche adaptation through changes in protein\u2013protein interaction networks

In contrast to fossorial and above-ground organisms, subterranean species have adapted to the extreme stresses of living underground. We analyzed the predicted protein–protein interactions (PPIs) of all gene products, including those of stress-response genes, among nine subterranean, ten fossorial, and 13 aboveground species. We considered 10,314 unique orthologous protein families and constructed 5,879,879 PPIs in all organisms using ChiPPI. We found strong association between PPI network modulation and adaptation to specific habitats, noting that mutations in genes and changes in protein sequences were not linked directly with niche adaptation in the organisms sampled. Thus, orthologous hypoxia, heat-shock, and circadian clock proteins were found to cluster according to habitat, based on PPIs rather than on sequence similarities. Curiously, "ordered" domains were preserved in aboveground species, while "disordered" domains were conserved in subterranean organisms, and confirmed for proteins in DistProt database. Furthermore, proteins with disordered regions were found to adopt significantly less optimal codon usage in subterranean species than in fossorial and above-ground species. These findings reveal design principles of protein networks by means of alterations in protein domains, thus providing insight into deep mechanisms of evolutionary adaptation, generally, and particularly of species to underground living and other confined habitats.

Codon usage pattern analysis of Gnetum luofuense (Gnetales) based on transcriptome data

AbstractThe Gnetum genus is an important medical, grain, and oil crop with ambiguous phylogenetic placement in seed plants. In the current study, full‐length transcripts from G. luofuense L. leaves were utilized for codon usage pattern analysis. For this, a total of 30,666 full‐length transcripts were used for analysis after data filtering. The GC content of all transcripts was 44.75%, with GC1 being the highest at 50.98%. Eighteen codons were identified as optimal codons, and 16 codons ending with A/U, indicating a higher frequency of A/T codon usage. Advanced analyses indicated that other factors, such as natural selection, play an important role in shaping the codon usage patterns in Gnetum. This study will be beneficial for understanding both the evolutionary mechanisms as well as the history of Gnetum genus.

Codon usage similarity between viral and some host genes suggests a codon-specific translational regulation

The codon usage pattern is a specific characteristic of each species; however, the codon usage of all of the genes in a genome is not uniform. Intriguingly, most viruses have codon usage patterns that are vastly different from the optimal codon usage of their hosts. How viral genes with different codon usage patterns are efficiently expressed during a viral infection is unclear. An analysis of the similarity between viral codon usage and the codon usage of the individual genes of a host genome has never been performed. In this study, we demonstrated that the codon usage of human RNA viruses is similar to that of some human genes, especially those involved in the cell cycle. This finding was substantiated by its concordance with previous reports of an upregulation at the protein level of some of these biological processes. It therefore suggests that some suboptimal viral codon usage patterns may actually be compatible with cellular translational machineries in infected conditions.

Codon optimization: a mathematical programing approach.

Synthesizing proteins in heterologous hosts is an important tool in biotechnology. However, the genetic code is degenerate and the codon usage is biased in many organisms. Synonymous codon changes that are customized for each host organism may have a significant effect on the level of protein expression. This effect can be measured by using metrics, such as codon adaptation index, codon pair bias, relative codon bias and relative codon pair bias. Codon optimization is designing codons that improve one or more of these objectives. Currently available algorithms and software solutions either rely on heuristics without providing optimality guarantees or are very rigid in modeling different objective functions and restrictions. We develop an effective mixed integer linear programing (MILP) formulation, which considers multiple objectives. Our numerical study shows that this formulation can be effectively used to generate (Pareto) optimal codon designs even for very long amino acid sequences using a standard commercial solver. We also show that one can obtain designs in the efficient frontier in reasonable solution times and incorporate other complex objectives, such as mRNA secondary structures in codon design using MILP formulations. http://alpersen.bilkent.edu.tr/codonoptimization/CodonOptimization.zip.

Comprehensive study of the genes involved in chlorophyll synthesis and degradation pathways in some monocot and dicot plant species

Chlorophyll (Chl) biosynthesis is one of the most important cellular processes essential for plant photosynthesis. Chl degradation pathway is also important catabolic process occurs during leaf senescence, fruit ripening and under biotic or abiotic stress conditions. Here we have systematically investigated the molecular evolution, gene structure, compositional analysis along with ENc plot, correspondence analysis and codon usage bias of the proteins and encoded genes involved in Chl metabolism from monocots and dicots. The gene and species specific phylogenetic trees using amino acid sequences showed clear clustering formation of the selected species based on monocots and dicots but not supported by 18S rRNA. Nucleotide composition of the encoding genes showed that average GC%, GC1%, GC2% and GC3% were higher in monocots. RSCU analysis depicts that genes from monocots for both pathways and genes for synthesis pathway from dicots only biased to G/C-ending synonymous codons but in degradation pathway most optimal codons (except UUG) in dicots biased to A/U-ending synonymous codons. We found strong evidence of episodic diversifying selection at several amino acid sites in all genes investigated. Conserved domain and gene structures were observed for the genes with varying lengths of introns and exons, involved in Chl metabolism along with some intronless genes within synthesis pathway. ENc and correspondence analyses suggested the mutational or selection constraint on the genes to shape the codon usage. These comprehensive studies may be helpful in further research in molecular phylogenetics and genomics and to better understand the evolutionary dynamics of Chl metabolic pathway. Communicated by Ramaswamy H. Sarma

The combined influence of codon composition and tRNA copy number regulates translational efficiency by influencing synonymous nucleotide substitution.

Codon usage bias is an important genomic phenomenon, where highly expressed genes use optimal codons for smoother translation with high yield, facilitated by the cognate tRNAs. Here, we presented the tRNA co-adaptation index (co-AI) by correlating tRNA gene copy number and codon composition in Saccharomyces cerevisiae. We observed that this co-AI is positively correlated with protein abundance and translation rate. Considering nucleotide substitutions, co-AI influences synonymous substitutions more than gene expression and protein abundance, the most important determinants of evolutionary rate. Co-AI correlates positively with mRNA secondary structure stability and mRNA half-life, which may lead to protein accumulation under high co-AI. However, the highly expressed proteins encoded by high co-AI genes are assisted by molecular chaperones to attain their proper functional conformation and prevent accumulation.

Genome-wide codon usage pattern analysis reveals the correlation between codon usage bias and gene expression in Cuscuta australis

The protein-coding genes and pseudogenes of Cuscuta australis had the diverse contribution to the formation and evolution of parasitism. The codon usage pattern analysis of these two type genes could be used to understand the gene transcription and translation. In this study, we systematically analyzed the codon usage patterns of protein-coding sequences and pseudogenes sequences in C. australis. The results showed that the high frequency codons of protein coding sequences and pseudogenes had the same A/U bias in the third position. However, these two sequences had converse bias at the third base in optimal codons: the protein coding sequences preferred G/C-ending codons while pseudogene sequences preferred A/U-ending codons. Neutrality plot and effective number of codons plot revealed that natural selection played a more important role than mutation pressure in two sequences codon usage bias. Furthermore, the gene expression level had a significant positive correlation with codon usage bias in C. australis. Highly-expressed protein coding genes exhibited a higher codon bias than lowly-expressed genes. Meanwhile, the high-expression genes tended to use G/C-ending synonymous codons. This result further verified the optimal codons usage bias and its correlation with the gene expression in C. australis.

Codon optimization by 0-1 linear programming

The problem of choosing an optimal codon sequence arises when synthetic protein-coding genes are added to cloning vectors for expression within a non-native host organism: to maximize yield, the chosen codons should have a high frequency in the host genome, but particular nucleotide bases sequences (called “motifs”) should be avoided or, instead, included. Dynamic programming (DP) has successfully been used in previous approaches to this problem. However, DP has a computational limit, especially when long motifs are forbidden, and does not allow control of motif positioning and combination. We reformulate the problem as an integer linear program (IP) and show that, with the same computational resources, one can easily solve problems with much more nucleotide bases and much longer forbidden/desired motifs than with DP. Moreover, IP (i) offers more flexibility than DP to treat constraints/objectives of different nature, and (ii) can efficiently deal with newly discovered critical motifs by dynamically re-optimizing additional variables and mathematical constraints.

Codon usage by chloroplast gene is bias in Hemiptelea davidii

The base composition of the chloroplast genes is of great interest because they play a highly significant role in the evolutionary development of the plants. Evaluation of the 48 chloroplast protein-coding genes of Hemiptelea davidii showed that the average GC content was about 37.32%, while at the third codon base position alone the average GC content was only 27.80%. The 48 genes were classified into five groups based on the gene function and each group displayed specific codon characteristics. Based on the relative synonymous codon usage analysis, a total of 30 high-frequency codons and 11 optimal codons were identified, most of them ended with A or T. Neutrality plot, ENC-plot and PR2-plot analyses showed that the codon usage bias of the chloroplast genes of H. davidii was greatly influenced by natural selection pressures. Meanwhile, the frequency of codon usage of chloroplast genes among different plant species displayed similarities, with some synonymous codons were preferred to be used in H. davidii. In this study, the codon usage pattern of the chloroplast protein coding genes of H. davidii provides us with a better understanding of the expression of chloroplast genes, and may advice the future molecular breeding programmes.

CSO – A sequence optimization software for engineering chloroplast expression in Chlamydomonas reinhardtii

Algal chloroplasts are promising hosts for expression of heterologous proteins. In contrast to the nuclear genome, these organelles lack transgene silencing mechanisms, making them more susceptible to genetic manipulation. While it is well established that codon selection greatly affects heterologous expression, a chloroplast-specific software for application of different sequence optimization algorithms is still missing. In this work we built CSO - a graphical user interface allowing users to engineer their genes for chloroplast expression in the model microalga Chlamydomonas reinhardtii. Within the software, users can choose between three different powerful codon selection algorithms which were built specifically for chloroplast expression: Optimal codons and folding, ChimeraMap, and Mimic original host. To provide users with general intuition regarding the performance of these algorithms, we designed different mCherry reporter genes, using each of the software algorithms. We transformed and expressed each of them in the chloroplast of C. reinhardtii, and quantified protein and mRNA abundance, alongside overall growth rates. For the reporter tested here, Mimic original host yielded the best results, though it had a lower Codon Adaptation Index score; while the algorithm supporting the highest expression could change depending on the target gene, our observations show that matching the chloroplast codon usage bias alone does not necessarily maximize expression, and that optimizing more complex sequence features could prove beneficial. CSO is freely available online; a link to its installation and download page is given in Section 3.1.

Characterization and comparison of chloroplast genomes from two sympatric Hippophae species (Elaeagnaceae)

The genus Hippophae includes deciduous shrubs or small trees, which provide many ecological, economic, and social benefits. We assembled and annotated the chloroplast genomes of sympatric Hippophae gyantsensis (Rousi) Lian and Hippophae rhamnoides Linn subsp. yunnanensis Rousi and comparatively analyzed their sequences. The full-length chloroplast genomes of H. gyantsensis and H. rhamnoides subsp. yunnanensis were 155,260 and 156,415 bp, respectively; both featured a quadripartite structure with two copies of a large inverted repeat (IR) separated by small (SSC) and large (LSC) single-copy regions. Each Hippophae chloroplast genome contained 131 genes, comprising 85 protein-coding, 8 ribosomal RNA, and 38 transfer RNA genes. Of 1302 nucleotide substitutions found between these two genomes, 824 (63.29%) occurred in the intergenic region or intron sequences, and 478 (36.71%) were located in the coding sequences. The SSC region had the highest mutation rate, followed by the LSC region and IR regions. Among the protein-coding genes, three had a ratio of nonsynonymous to synonymous substitutions (Ka/Ks) > 1 yet none were significant, and 66 had Ka/Ks < 1, of which 46 were significant. We found 20 and 16 optimal codons, most of which ended with A or U, for chloroplast protein-coding genes of H. gyantsensis and H. rhamnoides subsp. yunnanensis, respectively. Phylogenetic analysis of five available whole chloroplast genome sequences in the family Elaeagnaceae—using one Ziziphus jujube sequence as the outgroup—revealed that all five plant species formed a monophyletic clade with two subclades: one subclade consisted of three Hippophae species, while the other was formed by two Elaeagnus species, supported by 100% bootstrap values. Together, these results suggest the chloroplast genomes among Hippophae species are conserved, both in structure and gene composition, due to general purifying selection; like many other plants, a significant AT preference was discerned for most protein-coding genes in the Hippophae chloroplast genome. This study provides a valuable reference tool for future research on the general characteristics and evolution of chloroplast genomes in the genus Hippophae.

Quantitative Analysis of Spatial Distributions of All tRNA Genes in Budding Yeast

In the budding yeast nucleus, transfer RNA (tRNA) genes are considered to localize in the vicinity of the nucleolus; however, the use of Hi-C and fluorescent repressor-operator system techniques has clearly indicated that the tRNA genes are distributed not only around the nucleolus but also at other nuclear locations. However, there are some discrepancies between Hi-C data analysis and the results indicated from fluorescence microscopy data. To fill these gaps, we systematically clarified the spatial arrangements of all tRNA genes in the budding yeast nucleus using the genome simulation model developed by us. The simulation results revealed that out of 275 tRNA genes, 58% were found to be spatially distributed around the centromeres, 16% were distributed around the ribosomal DNA regions, and the remaining 26% were distributed between the centromeres and ribosomal DNA regions. Furthermore, 1% of all tRNA genes were found to be spatially distributed around the nuclear envelope, 30% were distributed around the center of the nucleus, and the remaining 69% were distributed between the nuclear envelope and the center of the nucleus. The percentage distributions were highly similar to those of the 176 tRNA genes encoding tRNAs having an anticodon for the optimal codons. The simulation results also revealed that the spatial arrangements of tRNA genes were affected by linear genomic distance from the tethering elements such as the centromeres or telomeres; however, the distance was only one of the factors to determine spatial distribution. This study also investigates whether tRNA gene transcriptional levels depend on the arrangements in the budding yeast nucleus by integrating the genome simulation model with tRNA sequencing data. The results suggest that the transcriptional levels did not depend on the arrangements in the nucleus. By using the genome simulation model, we showed the possibility of quantitatively analyzing genome structures.