Comparative analysis of complete Artemisia subgenus Seriphidium (Asteraceae: Anthemideae) chloroplast genomes: insights into structural divergence and phylogenetic relationships

Organelle genomes of two Scaevola species, S. taccada and S. hainanensis, provide new insights into evolutionary divergence between Scaevola and its related species

Chloroplast and mitochondrial genomes harbor crucial information that can be utilized for elucidating plant evolution and environmental adaptation. The organellar genomic characteristics of Goodeniaceae, a sister family to Asteraceae, remain unexplored. Here, using a combination of short-read and long-read sequencing technologies, we successfully assembled the complete organellar genomes of two Goodeniaceae species native to China, Scaevola taccada and S. hainanensis. Chloroplast genome collinearity analysis revealed that Scaevola expanded its genome length through inverted repeat expansion and large single copy fragment duplication, resulting in 181,022 bp (S. taccada) and 182,726 bp (S. hainanensis), ~30 kb increase compared to its related species. Mitochondrial genomes of two Scaevola species exhibit multi-ring topology, forming dual mitochondrial chromosomes of 314,251 bp (S. taccada) and 276,175 bp (S. hainanensis). Sequence variation analysis demonstrated substantial chloroplast sequence divergence (Pi = 0.45) and an increase in gene copy number within the genus. Relative synonymous codon usage (RSCU) analysis revealed that Scaevola chloroplast has a higher bias for A/U-ending codons than mitochondria, with chloroplasts RSCU values ranging from 0.32 to 1.94, whereas mitochondrial RSCU values ranging from 0.38 to 1.62. Phylogenetic analyses support the monophyly of the Asteraceae-Goodeniaceae sister group, whereas the extended evolutionary branches of Scaevola, coupled with mitochondrial collinearity analysis, indicate rapid organellar genome evolution of Scaevola. Organellar-nuclear horizontal gene transfer analysis identified specific increased in the copy numbers of photosynthesis-related genes and chloroplast-nuclear transfer events in S. taccada. Our study not only provides insights for understanding environmental adaptation mechanisms of coastal plants, but also contributes to elucidating organellar genome evolution in Scaevola and Goodeniaceae.

Comparative chloroplast genome analysis of Ardisia (Myrsinoideae, Primulaceae) in China and implications for phylogenetic relationships and adaptive evolution

BACKGROUND

Numerous species of Ardisia are widely used for their medicinal and ornamental values in China. However, accurately identifying Ardisia species at the molecular level remains a challenge due to the morphological similarities among different species, the complexity of interspecific variation, and the limited availability of genetic markers. In this study, we reported 20 chloroplast genomes of Ardisia species from China and combined them with 8 previously published chloroplast genomes to conduct a comprehensive analysis for phylogenetic relationships and adaptive evolution.

RESULTS

For the 28 Ardisia species analyzed in this study, the size of the chloroplast genomes ranged from 155,088 bp to 156,999 bp, and all exhibited a typical tetrad structure with conserved gene content and number. Each genome contained 85-88 protein-coding genes, 36-37 tRNA genes, and 8 rRNA genes. Comparative analysis showed that the genomic structures and gene order were relatively conserved with slight variations in the inverted repeat regions (IRs). Simple sequence repeats (SSRs) were predominantly single nucleotide repeats, while repeat sequences were mainly composed of palindromic and forward repeats. Twelve highly variable regions were identified as potential DNA barcodes for species identification and phylogenetic analysis of Ardisia. The phylogenetic tree supported the division of the subgenus Bladhia s.l. into two subgenera: Bladhia s.str. and Odontophylla (Yang) Huang. Further investigation revealed that two protein-coding genes (rbcL and rpoC2) were under positive selection and might be associated with the adaptation of Ardisia species to shaded environments.

CONCLUSION

Our study analyzed the chloroplast genomes of 20 Ardisia species from China to explore their phylogenetic relationships and adaptive evolution. By combining these results with data from eight previously published chloroplast genomes, the essential characteristics of Ardisia chloroplast genomes were clarified. The research establishes a theoretical basis for the classification, identification, and comprehension of the adaptive evolution of Ardisia species.

Comparative analysis of complete chloroplast genomes of 14 Asteraceae species

BACKGROUND

The Asteraceae family, the largest and one of the most diverse families of angiosperms, presents significant challenges in taxonomic classification and systematic research due to its vast species diversity and morphological complexity. A comprehensive understanding of the chloroplast genomes within this family is essential for refining taxonomic classifications and advancing phylogenetic studies.

METHODS AND RESULTS

In this study, we sequenced the complete chloroplast genomes of 14 Asteraceae species and conducted a thorough bioinformatic analysis of their characteristics. The chloroplast genomes, ranging from 150,907 bp to 152,858 bp, exhibit a typical quadripartite structure: a large single-copy (LSC) region (83,044 bp to 84,625 bp), a small single-copy (SSC) region (18,223 bp to 18,673 bp), and a pair of inverted repeats (IRs) (24,806 bp to 25,201 bp). These genomes encode 87 to 89 protein-coding genes (PCGs), 36 to 37 tRNA genes, and 8 rRNA genes, with high conservation in size, structure, gene content, and order. Comparative analysis with other Asteraceae species' chloroplast genomes revealed notable similarities and structural variations, particularly in the IR regions. Nucleotide polymorphism analysis identified four genes-trnY-GUA, trnE-UUC, ycf1, and rrn23-with higher Pi values, suggesting potential hotspots for evolutionary studies. Phylogenetic analysis using maximum likelihood (ML) and Bayesian inference (BI) approaches provided new insights, proposing the reclassification of Himalaiella auriculata and Jacobaea raphanifolia as independent genera, distinct from Saussurea and Senecio.

CONCLUSIONS

This study presents a comprehensive analysis of the chloroplast genome structures and phylogenetic relationships of 14 Asteraceae species, offering critical data for future molecular identification, evolutionary biology, and population genetics research. The findings hold significant implications for the ongoing refinement of Asteraceae taxonomic classifications and enhance our understanding of the evolutionary dynamics within this complex family.

Characterization of the complete chloroplast genome sequence of Artemisia sylvatica Maximowicz 1859 (Asteraceae)

Artemisia sylvatica Maximowicz 1859 is one of the medicinal herbs in Artemisia. This study presents the complete chloroplast genome of A. sylvatica, sequenced using the Illumina NovaSeq platform. The genome is 151,161 bp in length, featuring a GC content of 38%. It consists of a large single-copy (LSC) region of 82,892 bp, a small single-copy (SSC) region of 18,353 bp, and two inverted repeat (IR) regions of 24,958 bp each. In total, the genome contains 132 genes, including 87 protein-coding genes, 37 tRNA genes, and 8 rRNA genes. Phylogenetic analysis positions A. sylvatica within the subgenus Artemisia, highlighting its evolutionary relationships within this diverse genus. The first chloroplast genome of A. sylvatica was reported in this work contributes to the enrichment of genomic data for the genus Artemisia.

Complete chloroplast genome sequence of Artemisia littoricola (Asteraceae) from Dokdo Island Korea: genome structure, phylogenetic analysis, and biogeography study

The Asteraceae family, particularly the Artemisia genus, presents taxonomic challenges due to limited morphological characteristics and frequent natural hybridization. Molecular tools, such as chloroplast genome analysis, offer solutions for accurate species identification. In this study, we sequenced and annotated the chloroplast genome of Artemisia littoricola sourced from Dokdo Island, employing comparative analyses across six diverse Artemisia species. Our findings reveal conserved genome structures with variations in repeat sequences and junction boundaries. Notably, the chloroplast genome of A. littoricola spans 150,985 bp, consistent with other Artemisia species, and comprises 131 genes, including 86 protein-coding, 37 tRNA, and 8 rRNA genes. Among these genes, 16 possess a single intron, while clpP and ycf3 exhibit two introns each. Furthermore, 18 genes display duplicated copies within the IR regions. Moreover, the genome possesses 42 Simple Sequence Repeats (SSRs), predominantly abundant in A/T content and located within intergenic spacer regions. The analysis of codon usage revealed that the codons for leucine were the most frequent, with a preference for ending with A/U. While the chloroplast genome exhibited conservation overall, non-coding regions showed lower conservation compared to coding regions, with the Inverted Repeat (IR) region displaying higher conservation than single-copy regions. Phylogenetic analyses position A. littoricola within subgenus Dracunculus, indicating a close relationship with A. scoparia and A. desertorum. Additionally, biogeographic reconstructions suggest ancestral origins in East Asia, emphasizing Mongolia, China (North East and North Central and South Central China), and Korea. This study underscores the importance of chloroplast genomics in understanding Artemisia diversity and evolution, offering valuable insights into taxonomy, evolutionary patterns, and biogeographic history. These findings not only enhance our understanding of Artemisia's intricate biology but also contribute to conservation efforts and facilitate the development of molecular markers for further research and applications in medicine and agriculture.

A comparative analysis of chloroplast genomes revealed the chloroplast heteroplasmy of Artemisia annua

Artemisia annua L. is the main source of artemisinin, an antimalarial drug. High diversity of morphological characteristics and artemisinin contents of A. annua has affected the stable production of artemisinin while efficient discrimination method of A. annua strains is not available. The complete chloroplast (cp) genomes of 38 A. annua strains were assembled and analyzed in this study. Phylogenetic analysis of Artemisia species showed that distinct intraspecific divergence occurred in A. annua strains. A total of 38 A. annua strains were divided into two distinct lineages, one lineage containing widely-distributed strains and the other lineage only containing strains from northern China. The A. annua cp genomes ranged from 150, 953 to 150, 974 bp and contained 131 genes, and no presence or absence variation of genes was observed. The IRs and SC junctions were located in rps19 and ycf1, respectively, without IR contraction observed. Rich sequence polymorphisms were observed among A. annua strains, and a total of 60 polymorphic sites representing 14 haplotypes were identified which unfolding the cpDNA heteroplasmy of A. annua. In conclusion, this study provided valuable resource for A. annua strains identification and provided new insights into the evolutionary characteristics of A. annua.

Comparative analysis of complete chloroplast genomes of Synotis species (Asteraceae, Senecioneae) for identification and phylogenetic analysis

BACKGROUND

The Synotis (C. B. Clarke) C. Jeffrey & Y. L. Chen is an ecologically important genus of the tribe Senecioneae, family Asteraceae. Because most species of the genus bear similar morphology, traditional morphological identification methods are very difficult to discriminate them. Therefore, it is essential to develop a reliable and effective identification method for Synotis species. In this study, the complete chloroplast (cp.) genomes of four Synotis species, S. cavaleriei (H.Lév.) C. Jeffrey & Y.L. Chen, S. duclouxii (Dunn) C. Jeffrey & Y.L. Chen, S. nagensium (C.B. Clarke) C. Jeffrey & Y.L. Chen and S. erythropappa (Bureau & Franch.) C. Jeffrey & Y. L. Chen had been sequenced using next-generation sequencing technology and reported here.

RESULTS

These four cp. genomes exhibited a typical quadripartite structure and contained the large single-copy regions (LSC, 83,288 to 83,399 bp), the small single-copy regions (SSC, 18,262 to 18,287 bp), and the inverted repeat regions (IR, 24,837 to 24,842 bp). Each of the four cp. genomes encoded 134 genes, including 87 protein-coding genes, 37 tRNA genes, 8 rRNA genes, and 2 pseudogenes (ycf1 and rps19). The highly variable regions (trnC-GCA-petN, ccsA-psaC, trnE-UUC-rpoB, ycf1, ccsA and petN) may be used as potential molecular barcodes. The complete cp. genomes sequence of Synotis could be used as the potentially effective super-barcode to accurately identify Synotis species. Phylogenetic analysis demonstrated that the four Synotis species were clustered into a monophyletic group, and they were closed to the Senecio, Crassocephalum and Dendrosenecio in tribe Senecioneae.

CONCLUSIONS

This study will be useful for further species identification, evolution, genetic diversity and phylogenetic studies within this genus Synotis and the tribe Senecioneae.

Complete Plastid Genome Sequences of Four Salsoleae s.l. Species: Comparative and Phylogenetic Analyses

The taxonomic classification of the genera Salsola L., Pyankovia Akhani and Roalson, and Xylosalsola Tzvelev within Chenopodiaceae Vent. (Amaranthaceae s.l.) remains controversial, with the precise number of species within these genera still unresolved. This study presents a comparative analysis of the complete plastid genomes of S. foliosa, S. tragus, P. affinis, and X. richteri species collected in Kazakhstan. The assembled plastid genomes varied in length, ranging from 151,177 bp to 152,969 bp for X. richteri and S. tragus. These genomes contained 133 genes, of which 114 were unique, including 80 protein-coding, 30 tRNA, and 4 rRNA genes. Thirteen regions, including ndhC-ndhD, rps16-psbK, petD, rpoC2, ndhA, petB, clpP, atpF, ycf3, accD, ndhF-ndhG, matK, and rpl20-rpl22, exhibited relatively high levels of nucleotide variation. A total of 987 SSRs were detected across the four analyzed plastid genomes, primarily located in the intergenic spacer regions. Additionally, 254 repeats were identified, including 92 tandem repeats, 88 forward repeats, 100 palindromic repeats, and only one reverse repeat. A phylogenetic analysis revealed clear clustering into four clusters corresponding to the Salsoleae and Caroxyloneae tribe clades. These nucleotide sequences obtained in this study represent a valuable resource for future phylogenetic analyses within the Salsoleae s.l. tribe.

Comparative and phylogenetic analysis of the complete chloroplast genomes of 10 Artemisia selengensis resources based on high-throughput sequencing

BACKGROUND

Artemisia selengensis, classified within the genus Artemisia of the Asteraceae family, is a perennial herb recognized for its dual utility in culinary and medicinal domains. There are few studies on the chloroplast genome of A. selengensis, and the phylogeographic classification is vague, which makes phylogenetic analysis and evolutionary studies very difficult.

RESULTS

The chloroplast genomes of 10 A. selengensis in this study were highly conserved in terms of gene content, gene order, and gene intron number. The genome lengths ranged from 151,148 to 151,257 bp and were typical of a quadripartite structure with a total GC content of approximately 37.5%. The chloroplast genomes of all species encode 133 genes, including 88 protein-coding genes, 37 tRNA genes, and 8 rRNA genes. Due to the contraction and expansion of the inverted repeats (IR), the overlap of ycf1 and ndhF genes occurred at the inverted repeats B (IRB) and short single copy sequence (SSC) boundaries. According to a codon use study, the frequent base in the chloroplast genome of A. selengensis' third codon position was A/T. The number of SSR repeats was 42-44, most of which were single nucleotide A/T repeats. Sequence alignment analysis of the chloroplast genome showed that variable regions were mainly distributed in single copy regions, nucleotide diversity values of 0 to 0.009 were calculated by sliding window analysis, 8 mutation hotspot regions were detected, and coding regions were more conserved than non-coding regions. Analysis of non-synonymous substitution (Ka) and synonymous substitution (Ks) revealed that accD, rps12, petB, and atpF genes were affected by positive selection and no genes were affected by neutral selection. Based on the findings of the phylogenetic analysis, Artemisia selengensis was sister to the genus Artemisia Chrysanthemum and formed a monophyletic group with other Artemisia genera.

CONCLUSIONS

In this research, the present study systematically compared the chloroplast genomic features of A. selengensis and provided important information for the study of the chloroplast genome of A. selengensis and the evolutionary relationships among Asteraceae species.

Plastid genomes provide insights into the phylogeny and chloroplast evolution of the paper daisy tribe Gnaphalieae (Asteraceae)

Chloroplast genomes, as an essential source of phylogenetic information, are increasingly utilized in the evolutionary study of angiosperms. Gnaphalieae is a medium-sized tribe of the sunflower family of Asteraceae, with about 2,100 species in 178 genera distributed in temperate habitats worldwide. There has been considerable progress in our understanding of their phylogenetic evolution using both nuclear and chloroplast sequences, but no focus on chloroplast genomic data. In this study, we performed sequencing, assembly, and annotation of 16 representative chloroplast genomes from all the major lineages of Gnaphalieae. Our results showed that the plastomes exhibited a typical circular tetrad structure with similar genomic structure gene content. But there were differences in genome size, SSRs, and codon usage within the tribe. Phylogenetic analysis revealed Relhania clade is the earliest diverged lineages with the Lasiopogon clade and the Gnaphalium s.s. clade diverged subsequently. The core group includes FLAG clade sister to the HAP and Australasian group. Compared with the outgroup species, chloroplast genome size of the FLAG clade is much reduced whereas those of Australasian, HAP, Gnaphalium s.s., Lasiopogon and Relhania clades are relatively expanded. Insertions and deletions in the intergenic regions associated with repetitive sequence variations are supposed to be the main factor leading to length variations in the chloroplast genomes of Gnaphalieae. The comparative analyses of chloroplast genomes would provide useful implications into understanding the taxonomic and evolutionary history of Gnaphalieae.

The complete plastomes of thirteen Libanotis (Apiaceae, Apioideae) plants: comparative and phylogenetic analyses provide insights into the plastome evolution and taxonomy of Libanotis

BACKGROUND

The genus Libanotis Haller ex Zinn, nom. cons., a contentious member of Apiaceae, encompasses numerous economically and medicinally significant plants, comprising approximately 30 species distributed across Eurasia. Despite many previous taxonomic insights into it, phylogenetic studies of the genus are still lacking. And the establishment of a robust phylogenetic framework remains elusive, impeding advancements and revisions in the taxonomic system for this genus. Plastomes with greater variability in their genetic characteristics hold promise for building a more robust Libanotis phylogeny.

RESULTS

During our research, we sequenced, assembled, and annotated complete plastomes for twelve Libanotis species belong to three sections and two closely related taxa. We conducted a comprehensive comparative analysis through totally thirteen Libanotis plastomes for the genus, including an additional plastome that had been published. Our results suggested that Libanotis plastome was highly conserved between different subclades, while the coding regions were more conserved than the non-coding regions, and the IR regions were more conserved than the single copy regions. Nevertheless, eight mutation hotspot regions were identified among plastomes, which can be considered as candidate DNA barcodes for accurate species identification in Libanotis. The phylogenetic analyses generated a robustly framework for Libanotis and revealed that Libanotis was not a monophyletic group and their all three sections were polygenetic. Libanotis schrenkiana was sister to L. sibirica, type species of this genus, but the remainders scattered within Selineae.

CONCLUSION

The plastomes of Libanotis exhibited a high degree of conservation and was effective in enhancing the support and resolution of phylogenetic analyses within this genus. Based on evidence from both phylogeny and morphology, we propose the recognition of "Libanotis sensu stricto" and provide taxonomic recommendations for other taxa that previously belonged to Libanotis. In conclusion, our study not only revealed the phylogenetic position and plastid evolution of Libanotis, but also provided new insights into the phylogeny of the family Apiaceae and phylogenetic relationships within the tribe Selineae.

Characterization and phylogenetic analysis of the complete chloroplast genome of Saussurea sagittifolia (Asteraceae, Cardueae)

The species of Saussurea sagittifolia Y. S. Chen & S. R. Yi belongs to the family Asteraceae (Cardueae). The complete chloroplast genome of S. sagittifolia was assembled and annotated for the first time in this study. The complete chloroplast genome of S. sagittifolia was 152,535 bp, including a large single-copy (LSC) region of 83,511 bp, a small single-copy (SSC) region of 18,632 bp, and a pair of inverted repeats (IRs) of 25,196 bp. The overall GC content of the chloroplast genome was 37.7%. The chloroplast genome encoded 131 genes, including 87 protein-coding genes, 36 tRNA genes, and eight rRNA genes. Phylogenetic analysis based on complete chloroplast sequences revealed that it related closely to Saussurea medusa.

Complete plastid genome structure of 13 Asian Justicia (Acanthaceae) species: comparative genomics and phylogenetic analyses

BACKGROUND

Justicia L. is the largest genus in Acanthaceae Juss. and widely distributed in tropical and subtropical regions of the world. Previous phylogenetic studies have proposed a general phylogenetic framework for Justicia based on several molecular markers. However, their studies were mainly focused on resolution of phylogenetic issues of Justicia in Africa, Australia and South America due to limited sampling from Asia. Additionally, although Justicia plants are of high medical and ornamental values, little research on its genetics was reported. Therefore, to improve the understanding of its genomic structure and relationships among Asian Justicia plants, we sequenced complete chloroplast (cp.) genomes of 12 Asian plants and combined with the previously published cp. genome of Justicia leptostachya Hemsl. for further comparative genomics and phylogenetic analyses.

RESULTS

All the cp. genomes exhibit a typical quadripartite structure without genomic rearrangement and gene loss. Their sizes range from 148,374 to 151,739 bp, including a large single copy (LSC, 81,434-83,676 bp), a small single copy (SSC, 16,833-17,507 bp) and two inverted repeats (IR, 24,947-25,549 bp). GC contents range from 38.1 to 38.4%. All the plastomes contain 114 genes, including 80 protein-coding genes, 30 tRNAs and 4 rRNAs. IR variation and repetitive sequences analyses both indicated that Justicia grossa C. B. Clarke is different from other Justicia species because its lengths of ndhF and ycf1 in IRs are shorter than others and it is richest in SSRs and dispersed repeats. The ycf1 gene was identified as the candidate DNA barcode for the genus Justicia. Our phylogenetic results showed that Justicia is a polyphyletic group, which is consistent with previous studies. Among them, J. grossa belongs to subtribe Tetramerinae of tribe Justicieae while the other Justicia members belong to subtribe Justiciinae. Therefore, based on morphological and molecular evidence, J. grossa should be undoubtedly recognized as a new genus. Interestingly, the evolutionary history of Justicia was discovered to be congruent with the morphology evolution.

CONCLUSION

Our study not only elucidates basic features of Justicia whole plastomes, but also sheds light on interspecific relationships of Asian Justicia plants for the first time.