Comparative analysis of codon usage patterns in chloroplast genomes of ten Epimedium species

Comparative analysis of codon usage bias in the chloroplast genomes of eighteen Ampelopsideae species (Vitaceae)

BACKGROUND

The tribe Ampelopsideae plants are important garden plants with both medicinal and ornamental values. The study of codon usage bias (CUB) facilitates a deeper comprehension of the molecular genetic evolution of species and their adaptive strategies. The joint analysis of CUB in chloroplast genomes (cpDNA) offers valuable insights for in-depth research on molecular genetic evolution, biological resource conservation, and elite breeding within this plant family.

RESULTS

The base composition and codon usage preferences of the eighteen chloroplast genomes were highly similar, with the GC content of bases at all positions of their codons being less than 50%. This indicates that they preferred A/T bases. Their effective codon numbers were all in the range of 35-61, which indicates that the codon preferences of the chloroplast genomes of the 18 Ampelopsideae plants were relatively weak. A series of analyses indicated that the codon preference of the chloroplast genomes of the 18 Ampelopsideae plants was influenced by a combination of multiple factors, with natural selection being the primary influence. The clustering tree generated based on the relative usage of synonymous codons is consistent with some of the results obtained from the phylogenetic tree of chloroplast genomes, which indicates that the clustering tree based on the relative usage of synonymous codons can be an important supplement to the results of the sequence-based phylogenetic analysis. Eventually, 10 shared best codons were screened on the basis of the chloroplast genomes of 18 species.

CONCLUSION

The codon preferences of the chloroplast genome in Ampelopsideae plants are relatively weak and are primarily influenced by natural selection. The codon composition of the chloroplast genomes of the eighteen Ampelopsideae plants and their usage preferences were sufficiently similar to demonstrate that the chloroplast genomes of Ampelopsideae plants are highly conserved. This study provides a scientific basis for the genetic evolution of chloroplast genes in Ampelopsideae species and their suitable strategies.

Analysis of chloroplast genome structure and phylogeny of the traditional medicinal of Ardisia crispa (Myrsinaceae)

Ardisia crispa(Myrsinaceae) is an ethnomedicine with horticultural and important medicinal values. Its morphology is complex, and its identification is difficult. We analyse the chloroplast genome characteristics and phylogenetic position of A. crispa to provide basic research data for the identification of A. crispa species and resource conservation. This study assemble and annotate the chloroplast genome of A. crispa and to compare it with the chloroplast genome within Ardisia. The A. crispa chloroplast genome is 156,785 bp in length, with a typical quadripartite structure containing 131 genes, including 86 protein-coding genes, 37 tRNA genes, and 8 rRNA genes; a total of 59 SSRs sites were identified, and the codon preference of this chloroplast genome is greater in A/U than in G/C, and leucine is the amino acid with the highest frequency of use. The chloroplast genomes of the nine Ardisia species are conserved in gene content and number, with more stable boundaries and less variation. In the phylogenetic tree, A. crispa is clustered on a branch with A. crispa var dielsii, and is closely related to A. mamillata and A. pedalis. In this study, we constructed and analyzed the chloroplast genome structure of A. crispa, and conducted phylogenetic analysis using the whole chloroplast genome sequence data of Ardisia plants, which is of great significance in understanding the genetic basis of A. crispa and adaptive evolution in Ardisia plants, and this will lay the foundation for the future research on A. crispa resource conservation and species identification.

Phylogenomic analysis and dynamic evolution of chloroplast genomes of Clematis nannophylla

Clematis nannophylla is a perennial shrub of Clematis with ecological, ornamental, and medicinal value, distributed in the arid and semi-arid areas of northwest China. This study successfully determined the chloroplast (cp) genome of C. nannophylla, reconstructing a phylogenetic tree of Clematis. This cp genome is 159,801 bp in length and has a typical tetrad structure, including a large single-copy, a small single-copy, and a pair of reverse repeats (IRa and IRb). It contains 133 unique genes, including 89 protein-coding, 36 tRNA, and 8 rRNA genes. Additionally, 66 simple repeat sequences, 50 dispersed repeats, and 24 tandem repeats were found; many of the dispersed and tandem repeats were between 20-30 bp and 10-20 bp, respectively, and the abundant repeats were located in the large single copy region. The cp genome was relatively conserved, especially in the IR region, where no inversion or rearrangement was observed, further revealing that the coding regions were more conserved than the noncoding regions. Phylogenetic analysis showed that C. nannophylla is more closely related to C. fruticosa and C. songorica. Our analysis provides reference data for molecular marker development, phylogenetic analysis, population studies, and cp genome processes to better utilise C. nannophylla.

Comparative analysis of codon usage patterns in the chloroplast genomes of nine forage legumes

Leguminosae is one of the three largest families of angiosperms after Compositae and Orchidaceae. It is widely distributed and grows in a variety of environments, including plains, mountains, deserts, forests, grasslands, and even waters where almost all legumes can be found. It is one of the most important sources of starch, protein and oil in the food of mankind and also an important source of high-quality forage material for animals, which has important economic significance. In our study, the codon usage patterns and variation sources of the chloroplast genome of nine important forage legumes were systematically analyzed. Meanwhile, we also constructed a phylogenetic tree based on the whole chloroplast genomes and protein coding sequences of these nine forage legumes. Our results showed that the chloroplast genomes of nine forage legumes end with A/T bases, and seven identical high-frequency (HF) codons were detected among the nine forage legumes. ENC-GC3s mapping, PR2 analysis, and neutral analysis showed that the codon bias of nine forage legumes was influenced by many factors, among which natural selection was the main influencing factor. The codon usage frequency showed that the Nicotiana tabacum and Saccharomyces cerevisiae can be considered as receptors for the exogenous expression of chloroplast genes of these nine forage legumes. The phylogenetic relationships of the chloroplast genomes and protein coding genes were highly similar, and the nine forage legumes were divided into three major clades. Among the clades Melilotus officinalis was more closely related to Medicago sativa, and Galega officinalis was more closely related to Galega orientalis. This study provides a scientific basis for the molecular markers research, species identification and phylogenetic studies of forage legumes.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-024-01421-0.

Codon usage characterization and phylogenetic analysis of the mitochondrial genome in Hemerocallis citrina

BACKGROUND

Hemerocallis citrina Baroni is a traditional vegetable crop widely cultivated in eastern Asia for its high edible, medicinal, and ornamental value. The phenomenon of codon usage bias (CUB) is prevalent in various genomes and provides excellent clues for gaining insight into organism evolution and phylogeny. Comprehensive analysis of the CUB of mitochondrial (mt) genes can provide rich genetic information for improving the expression efficiency of exogenous genes and optimizing molecular-assisted breeding programmes in H. citrina.

RESULTS

Here, the CUB patterns in the mt genome of H. citrina were systematically analyzed, and the possible factors shaping CUB were further evaluated. Composition analysis of codons revealed that the overall GC (GCall) and GC at the third codon position (GC3) contents of mt genes were lower than 50%, presenting a preference for A/T-rich nucleotides and A/T-ending codons in H. citrina. The high values of the effective number of codons (ENC) are indicative of fairly weak CUB. Significant correlations of ENC with the GC3 and codon counts were observed, suggesting that not only compositional constraints but also gene length contributed greatly to CUB. Combined ENC-plot, neutrality plot, and Parity rule 2 (PR2)-plot analyses augmented the inference that the CUB patterns of the H. citrina mitogenome can be attributed to multiple factors. Natural selection, mutation pressure, and other factors might play a major role in shaping the CUB of mt genes, although natural selection is the decisive factor. Moreover, we identified a total of 29 high-frequency codons and 22 optimal codons, which exhibited a consistent preference for ending in A/T. Subsequent relative synonymous codon usage (RSCU)-based cluster and mt protein coding gene (PCG)-based phylogenetic analyses suggested that H. citrina is close to Asparagus officinalis, Chlorophytum comosum, Allium cepa, and Allium fistulosum in evolutionary terms, reflecting a certain correlation between CUB and evolutionary relationships.

CONCLUSIONS

There is weak CUB in the H. citrina mitogenome that is subject to the combined effects of multiple factors, especially natural selection. H. citrina was found to be closely related to Asparagus officinalis, Chlorophytum comosum, Allium cepa, and Allium fistulosum in terms of their evolutionary relationships as well as the CUB patterns of their mitogenomes. Our findings provide a fundamental reference for further studies on genetic modification and phylogenetic evolution in H. citrina.

An analysis of codon utilization patterns in the chloroplast genomes of three species of Coffea

BACKGROUND

The chloroplast genome of plants is known for its small size and low mutation and recombination rates, making it a valuable tool in plant phylogeny, molecular evolution, and population genetics studies. Codon usage bias, an important evolutionary feature, provides insights into species evolution, gene function, and the expression of exogenous genes. Coffee, a key crop in the global tropical agricultural economy, trade, and daily life, warrants investigation into its codon usage bias to guide future research, including the selection of efficient heterologous expression systems for coffee genetic transformation.

RESULTS

Analysis of the codon utilization patterns in the chloroplast genomes of three Coffea species revealed a high degree of similarity among them. All three species exhibited similar base compositions, with high A/T content and low G/C content and a preference for A/T-ending codons. Among the 30 high-frequency codons identified, 96.67% had A/T endings. Fourteen codons were identified as ideal. Multiple mechanisms, including natural selection, were found to influence the codon usage patterns in the three coffee species, as indicated by ENc-GC3s mapping, PR2 analysis, and neutral analysis. Nicotiana tabacum and Saccharomyces cerevisiae have potential value as the heterologous expression host for three species of coffee genes.

CONCLUSION

This study highlights the remarkable similarity in codon usage patterns among the three coffee genomes, primarily driven by natural selection. Understanding the gene expression characteristics of coffee and elucidating the laws governing its genetic evolution are facilitated by investigating the codon preferences in these species. The findings can enhance the efficacy of exogenous gene expression and serve as a basis for future studies on coffee evolution.

Comparative chloroplast genomics and insights into the molecular evolution of Tanaecium (Bignonieae, Bignoniaceae)

Species of Tanaecium (Bignonieae, Bignoniaceae) are lianas distributed in the Neotropics and centered in the Amazon. Members of the genus exhibit exceptionally diverse flower morphology and pollination systems. Here, we sequenced, assembled, and annotated 12 complete and four partial chloroplast genomes representing 15 Tanaecium species and more than 70% of the known diversity in the genus. Gene content and order were similar in all species of Tanaecium studied, with genome sizes ranging between 158,470 and 160,935 bp. Tanaecium chloroplast genomes have 137 genes, including 80-81 protein-coding genes, 37 tRNA genes, and four rRNA genes. No rearrangements were found in Tanaecium plastomes, but two different patterns of boundaries between regions were recovered. Tanaecium plastomes show nucleotide variability, although only rpoA was hypervariable. Multiple SSRs and repeat regions were detected, and eight genes were found to have signatures of positive selection. Phylogeny reconstruction using 15 Tanaecium plastomes resulted in a strongly supported topology, elucidating several relationships not recovered previously and bringing new insights into the evolution of the genus.

Complete chloroplast genomes of three wild perennial Hordeum species from Central Asia: genome structure, mutation hotspot, phylogenetic relationships, and comparative analysis

Hordeum L. is widely distributed in mountain or plateau of subtropical and warm temperate regions around the world. Three wild perennial Hordeum species, including H. bogdanii, H. brevisubulatum, and H. violaceum, have been used as forage and for grassland ecological restoration in high-altitude areas in recent years. To date, the degree of interspecies sequence variation in the three Hordeum species within existing gene pools is still not well-defined. Herein, we sequenced and assembled chloroplast (cp) genomes of the three species. The results revealed that the cp genome of H. bogdanii showed certain sequence variations compared with the cp genomes of the other two species (H. brevisubulatum and H. violaceum), and the latter two were characterized by a higher relative affinity. Parity rule 2 plot (PR2) analysis illuminated that most genes of all ten Hordeum species were concentrated in nucleotide T and G. Numerous single nucleotide polymorphism (SNP) and insertion/deletion (In/Del) events were detected in the three Hordeum species. A series of hotspots regions (tRNA-GGU ~ tRNA-GCA, tRNA-UGU ~ ndhJ, psbE ~ rps18, ndhF ~ tRNA-UAG, etc.) were identified by mVISTA procedures, and the five highly polymorphic genes (tRNA-UGC, tRNA-UAA, tRNA-UUU, tRNA-UAC, and ndhA) were proved by the nucleotide diversity (Pi). Although the distribution and existence of cp simple sequence repeats (cpSSRs) were predicted in the three Hordeum cp genomes, no rearrangement was found between them. A similar phenomenon has been found in the cp genome of the other seven Hordeum species, which has been published so far. In addition, evolutionary relationships were reappraised based on the currently reported cp genome of Hordeum L. This study offers a framework for gaining a better understanding of the evolutionary history of Hordeum species through the re-examination of their cp genomes, and by identifying highly polymorphic genes and hotspot regions that could provide important insights into the genetic diversity and differentiation of these species.

Codon Usage Analyses Reveal the Evolutionary Patterns among Plastid Genes of Saxifragales at a Larger-Sampling Scale

Saxifragales is a 15-family order of early-divergent Eudicots with a rich morphological diversity and an ancient rapid radiation. Codon usage bias (CUB) analyses have emerged as an essential tool for understanding the evolutionary dynamics in genes. Thus far, the codon utilization patterns had only been reported in four separate genera within Saxifragales. This study provides a comprehensive assessment of the codon manipulation based on 50 plastid genes, covering 11 constituent families at a larger sampling scale. Our results first showed a high preference for AT bases and AT-ending codons. We then used effective number of codons (ENC) to assess a range of codon bias levels in the plastid genes. We also detected high-informative intrafamilial differences of ENC in three families. Subsequently, parity rule 2 (PR2) plot analyses revealed both family-unique and order-shared bias patterns. Most importantly, the ENC plots and neutrality analyses collectively supported the dominant roles of selection in the CUB of Saxifragales plastid genes. Notably, the phylogenetic affinities inferred by both ML and BI methods were consistent with each other, and they all comprised two primary clades and four subclades. These findings significantly enhance our understanding of the evolutionary processes of the Saxifrage order, and could potentially inspire more CUB analyses at higher taxonomic levels.