Comparative analysis of plastomes in Oxalidaceae: Phylogenetic relationships and potential molecular markers

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

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

Complete chloroplast genome structural characterization of two Aerides (Orchidaceae) species with a focus on phylogenetic position of Aerides flabellata

BACKGROUND

The disputed phylogenetic position of Aerides flabellata Rolfe ex Downie, due to morphological overlaps with related species, was investigated based on evidence of complete chloroplast (cp) genomes. The structural characterization of complete cp genomes of A. flabellata and A. rosea Lodd. ex Lindl. & Paxton were analyzed and compared with those of six related species in "Vanda-Aerides alliance" to provide genomic information on taxonomy and phylogeny.

RESULTS

The cp genomes of A. flabellata and A. rosea exhibited conserved quadripartite structures, 148,145 bp and 147,925 bp in length, with similar GC content (36.7 ~ 36.8%). Gene annotations revealed 110 single-copy genes, 18 duplicated in inverted regions, and ten with introns. Comparative analysis across related species confirmed stable sequence identity and higher variation in single-copy regions. However, there are notable differences in the IR regions between two Aerides Lour. species and the other six related species. The phylogenetic analysis based on CDS from complete cp genomes indicated that Aerides species except A. flabellata formed a monophyletic clade nested in the subtribe Aeridinae, being a sister group to Renanthera Lour., consistent with previous studies. Meanwhile, a separate clade consisted of A. flabellata and six Vanda R. Br. species was formed, as a sister taxon to Holcoglossum Schltr.

CONCLUSIONS

This research was the first report on the complete cp genomes of A. flabellata. The results provided insights into understanding of plastome evolution and phylogenetic relationships of Aerides. The phylogenetic analysis based on complete cp genomes showed that A. flabellata should be placed in Vanda rather than in Aerides.

Low-coverage whole genome sequencing of diverse Dioscorea bulbifera accessions for plastome resource development, polymorphic nuclear SSR identification, and phylogenetic analyses

Dioscorea bulbifera (Dioscoreaceae), a versatile herbaceous climber native to Africa and Asia, holds significant nutritional and medicinal value. Despite extensive characterization and genetic variability analyses of African accessions, studies on the genetic variation of this species in China are limited. To address this gap, we conducted low-coverage whole genome sequencing on D. bulbifera accessions from diverse regions across mainland China and Taiwan island. Our initial investigation encompassed comprehensive comparative plastome analyses of these D. bulbifera accessions, and developing plastome resources (including plastome-derived repetitive sequences, SSRs, and divergent hotspots). We also explored polymorphic nuclear SSRs and elucidated the intraspecific phylogeny of these accessions. Comparative plastome analyses revealed that D. bulbifera plastomes exhibited a conserved quadripartite structure with minimal size variation mainly attributed to intergenic spacer regions, reinforcing prior observations of a high degree of conservation within a species. We identified 46 to 52 dispersed repeats and 151 to 163 plastome-derived SSRs, as well as highlighted eight key divergent hotspots in these D. bulbifera accessions. Furthermore, we developed 2731 high-quality candidate polymorphic nuclear SSRs for D. bulbifera. Intraspecific phylogenetic analysis revealed three distinct clades, where accessions from Southeast China formed a sister group to those from South China and Taiwan island, and collectively, these two clades formed a sister group to the remaining accessions, indicating potential regional genetic divergence. These findings not only contributed to the understanding of the genetic variation of D. bulbifera, but also offered valuable resources for future research, breeding efforts, and utilization of this economically important plant species.

Comparative Analysis of Plastomes in Elsholtzieae: Phylogenetic Relationships and Potential Molecular Markers

The Elsholtzieae, comprising ca. 7 genera and 70 species, is a small tribe of Lamiaceae (mint family). Members of Elsholtzieae are of high medicinal, aromatic, culinary, and ornamentals value. Despite the rich diversity and value of Elsholtzieae, few molecular markers or plastomes are available for phylogenetics. In the present study, we employed high-throughput sequencing to assemble two Mosla plastomes, M. dianthera and M. scabra, for the first time, and compared with other plastomes of Elsholtzieae. The plastomes of Elsholtzieae exhibited a quadripartite structure, ranging in size from 148,288 bp to 152,602 bp. Excepting the absence of the pseudogene rps19 in Elsholtzia densa, the exhaustive tally revealed the presence of 132 genes (113 unique genes). Among these, 85 protein-coding genes (CDS), 37 tRNA genes, 8 rRNA genes, and 2 pseudogenes (rps19 and ycf1) were annotated. Comparative analyses showed that the plastomes of these species have minor variations at the gene level. Notably, the E. eriostchya plastid genome exhibited increased GC content regions in the LSC and SSC, resulting in an increased overall GC content of the entire plastid genome. The E. densa plastid genome displayed modified boundaries due to inverted repeat (IR) contraction. The sequences of CDS and intergenic regions (IGS) with elevated variability were identified as potential molecular markers for taxonomic inquiries within Elsholtzieae. Phylogenetic analysis indicated that four genera formed monophyletic entities, with Mosla and Perilla forming a sister clade. This clade was, in turn, sister to Collinsonia, collectively forming a sister group to Elsholtzia. Both CDS, and CDS + IGS could construct a phylogenetic tree with stronger support. These findings facilitate species identification and DNA barcoding investigations in Elsholtzieae and provide a foundation for further exploration and resource utilization within this tribe.

Molecular phylogeny and inflorescence evolution of Prunus (Rosaceae) based on RAD-seq and genome skimming analyses

Prunus is an economically important genus widely distributed in the temperate Northern Hemisphere. Previous studies on the genus using a variety of loci yielded conflicting phylogenetic hypotheses. Here, we generated nuclear reduced representation sequencing data and plastid genomes for 36 Prunus individuals and two outgroups. Both nuclear and plastome data recovered a well-resolved phylogeny. The species were divided into three main clades corresponding to their inflorescence types, - the racemose group, the solitary-flower group and the corymbose group - with the latter two sister to one another. Prunus was inferred to have diversified initially in the Late Cretaceous around 67.32 million years ago. The diversification of the three major clades began between the Paleocene and Miocene, suggesting that paleoclimatic events were an important driving force for Prunus diversification. Ancestral state reconstructions revealed that the most recent common ancestor of Prunus had racemose inflorescences, and the solitary-flower and corymb inflorescence types were derived by reduction of flower number and suppression of the rachis, respectively. We also tested the hybrid origin hypothesis of the racemose group proposed in previous studies. Prunus has undergone extensive hybridization events, although it is difficult to identify conclusively specific instances of hybridization when using SNP data, especially deep in the phylogeny. Our study provides well-resolved nuclear and plastid phylogenies of Prunus, reveals substantial cytonuclear discord at shallow scales, and sheds new light on inflorescence evolution in this economically important lineage.

Complete chloroplast genome structural characterization of two Phalaenopsis (Orchidaceae) species and comparative analysis with their alliance

BACKGROUND

The taxonomy and infrageneric delimitation of Phalaenopsis Blume has been significantly disputed due to some overlapping morphological features between species related, which needed further evidence for clarification. The structural characterization of complete chloroplast genomes of P. storbatiana and P. wilsonii were analyzed and compared with those of related taxa to provide a better understanding of their genomic information on taxonomy and phylogeny.

RESULTS

It was shown that chloroplast genomes of Phalaenopsis storbatiana and P. wilsonii had a typical quadripartite structure with conserved genome arrangements and moderate divergence. The chloroplast genomes of P. storbatiana and P. wilsonii were 145,885 bp and 145,445 bp in length, respectively, and shared a similar GC content of 36.8%. Gene annotations of two species revealed 109 single-copy genes consistently. In addition, 20 genes duplicated in the inverted regions, 16 genes each possessed one or more introns, and five ndh (NA (D)H dehydrogenase) genes were observed in both. Comparative analysis of the total cp genomes of P. storbatiana and P. wilsonii with those of other six related Phalaenopsis species confirmed the stable sequence identity for coding and non-coding regions and higher sequence variation in SC regions than IR regions. Most of their protein-coding genes had a high degree of codon preference. Moreover, 45 genes were discovered with significantly positive selection. However, different amplifications in IR regions were observed in these eight species. Phylogenetic analysis based on CDS from 60 species representing main clades in Orchidaceae indicated that Phalaenopsis species including P. stobartiana and P. wilsonii formed a monophyletic clade with high bootstrap nested in tribe Vandeae of Epidendroideae, which was consistent with those from previous studies.

CONCLUSIONS

The results could provide insight into understanding the plastome evolution and phylogenetic relationships of Phalaenopsis.

Phylogenomics and phylogeography of Menispermum (Menispermaceae)

INTRODUCTION

Phylogenomics have been widely used to resolve ambiguous and controversial evolutionary relationships among plant species and genera, and the identification of unique indels in plastomes may even help to understand the evolution of some plant families. Menispermum L. (Menispermaceae) consists of three species, M. dauricum DC., M. canadense L., and M. mexicanum Rose, which are disjuncly distributed among East Asia, Eastern North America and Mexico. Taxonomists continue to debate whether M. mexicanum is a distinct species, a variety of M. dauricum, or simply a synonym of M. canadense. To date, no molecular systematics studies have included this doubtful species in phylogenetic analyses.

METHODS

In this study, we examined phylogenomics and phylogeography of Menispermum across its entire range using 29 whole plastomes of Menispermaceae and 18 ITS1&ITS2 sequences of Menispermeae. We reconstructed interspecific relationships of Menispermum and explored plastome evolution in Menispermaceae, revealing several genomic hotspot regions for the family.

RESULTS AND DISCUSSION

Phylogenetic and network analyses based on whole plastome and ITS1&ITS2 sequences show that Menispermum clusters into two clades with high support values, Clade A (M. dauricum) and Clade B (M. canadense + M. mexicanum). However, M. mexicanum is nested within M. canadense and, as a result, we support that M. mexicanum is a synonym of M. canadense. We also identified important molecular variations in the plastomes of Menispermaceae. Several indels and consequently premature terminations of genes occur in Menispermaceae. A total of 54 regions were identified as the most highly variable plastome regions, with nucleotide diversity (Pi) values > 0.05, including two coding genes (matK, ycf1), four introns (trnK intron, rpl16 intron, rps16 intron, ndhA intron), and 48 intergenic spacer (IGS) regions. Of these, four informative hotspot regions (trnH-psbA, ndhF-rpl32, trnK-rps16, and trnP-psaJ) should be especially useful for future studies of phylogeny, phylogeography and conservation genetics of Menispermaceae.

Complete Plastome of Physalis angulata var. villosa, Gene Organization, Comparative Genomics and Phylogenetic Relationships among Solanaceae

Physalis angulata var. villosa, rich in withanolides, has been used as a traditional Chinese medicine for many years. To date, few extensive molecular studies of this plant have been conducted. In the present study, the plastome of P. angulata var. villosa was sequenced, characterized and compared with that of other Physalis species, and a phylogenetic analysis was conducted in the family Solanaceae. The plastome of P. angulata var. villosa was 156,898 bp in length with a GC content of 37.52%, and exhibited a quadripartite structure typical of land plants, consisting of a large single-copy (LSC, 87,108 bp) region, a small single-copy (SSC, 18,462 bp) region and a pair of inverted repeats (IR: IRA and IRB, 25,664 bp each). The plastome contained 131 genes, of which 114 were unique and 17 were duplicated in IR regions. The genome consisted of 85 protein-coding genes, eight rRNA genes and 38 tRNA genes. A total of 38 long, repeat sequences of three types were identified in the plastome, of which forward repeats had the highest frequency. Simple sequence repeats (SSRs) analysis revealed a total of 57 SSRs, of which the T mononucleotide constituted the majority, with most of SSRs being located in the intergenic spacer regions. Comparative genomic analysis among nine Physalis species revealed that the single-copy regions were less conserved than the pair of inverted repeats, with most of the variation being found in the intergenic spacer regions rather than in the coding regions. Phylogenetic analysis indicated a close relationship between Physalis and Withania. In addition, Iochroma, Dunalia, Saracha and Eriolarynx were paraphyletic, and clustered together in the phylogenetic tree. Our study published the first sequence and assembly of the plastome of P. angulata var. villosa, reported its basic resources for evolutionary studies and provided an important tool for evaluating the phylogenetic relationship within the family Solanaceae.

The complete chloroplast genome sequences of three Broussonetia species and comparative analysis within the Moraceae

Background

Species of Broussonetia (family Moraceae) are commonly used to make textiles and high-grade paper. The distribution of Broussonetia papyrifera L. is considered to be related to the spread and location of humans. The complete chloroplast (cp) genomes of B. papyrifera, Broussonetia kazinoki Sieb., and Broussonetia kaempferi Sieb. were analyzed to better understand the status and evolutionary biology of the genus Broussonetia.

Methods

The cp genomes were assembled and characterized using SOAPdenovo2 and DOGMA. Phylogenetic and molecular dating analysis were performed using the concatenated nucleotide sequences of 35 species in the Moraceae family and were based on 66 protein-coding genes (PCGs). An analysis of the sequence divergence (pi) of each PCG among the 35 cp genomes was conducted using DnaSP v6. Codon usage indices were calculated using the CodonW program.

Results

All three cp genomes had the typical land plant quadripartite structure, ranging in size from 160,239 bp to 160,841 bp. The ribosomal protein L22 gene (RPL22) was either incomplete or missing in all three Broussonetia species. Phylogenetic analysis revealed two clades. Clade 1 included Morus and Artocarpus, whereas clade 2 included the other seven genera. Malaisia scandens Lour. was clustered within the genus Broussonetia. The differentiation of Broussonetia was estimated to have taken place 26 million years ago. The PCGs' pi values ranged from 0.0005 to 0.0419, indicating small differences within the Moraceae family. The distribution of most of the genes in the effective number of codons plot (ENc-plot) fell on or near the trend line; the slopes of the trend line of neutrality plots were within the range of 0.0363-0.171. These results will facilitate the identification, taxonomy, and utilization of the Broussonetia species and further the evolutionary studies of the Moraceae family.

Characterization of the plastome of Physaliscordata and comparative analysis of eight species of Physalis sensu stricto

In this study, we sequenced, assembled, and annotated the plastome of Physaliscordata Mill. and compared it with seven species of the genus Physalis sensu stricto. Sequencing, annotating, and comparing plastomes allow us to understand the evolutionary mechanisms associated with physiological functions, select possible molecular markers, and identify the types of selection that have acted in different regions of the genome. The plastome of P.cordata is 157,000 bp long and presents the typical quadripartite structure with a large single-copy (LSC) region of 87,267 bp and a small single-copy (SSC) region of 18,501 bp, which are separated by two inverted repeat (IRs) regions of 25,616 bp each. These values are similar to those found in the other species, except for P.angulata L. and P.pruinosa L., which presented an expansion of the LSC region and a contraction of the IR regions. The plastome in all Physalis species studied shows variation in the boundary of the regions with three distinct types, the percentage of the sequence identity between coding and non-coding regions, and the number of repetitive regions and microsatellites. Four genes and 10 intergenic regions show promise as molecular markers and eight genes were under positive selection. The maximum likelihood analysis showed that the plastome is a good source of information for phylogenetic inference in the genus, given the high support values and absence of polytomies. In the Physalis plastomes analyzed here, the differences found, the positive selection of genes, and the phylogenetic relationships do not show trends that correspond to the biological or ecological characteristics of the species studied.

Incomplete lineage sorting and reticulate evolution mask species relationships in Brunelliaceae, an Andean family with rapid, recent diversification

PREMISE

To date, phylogenetic relationships within the monogeneric Brunelliaceae have been based on morphological evidence, which does not provide sufficient phylogenetic resolution. Here we use target-enriched nuclear data to improve our understanding of phylogenetic relationships in the family.

METHODS

We used the Angiosperms353 toolkit for targeted recovery of exonic regions and supercontigs (exons + introns) from low copy nuclear genes from 53 of 70 species in Brunellia, and several outgroup taxa. We removed loci that indicated biased inference of relationships and applied concatenated and coalescent methods to infer Brunellia phylogeny. We identified conflicts among gene trees that may reflect hybridization or incomplete lineage sorting events and assessed their impact on phylogenetic inference. Finally, we performed ancestral-state reconstructions of morphological traits and assessed the homology of character states used to define sections and subsections in Brunellia.

RESULTS

Brunellia comprises two major clades and several subclades. Most of these clades/subclades do not correspond to previous infrageneric taxa. There is high topological incongruence among the subclades across analyses.

CONCLUSIONS

Phylogenetic reconstructions point to rapid species diversification in Brunelliaceae, reflected in very short branches between successive species splits. The removal of putatively biased loci slightly improves phylogenetic support for individual clades. Reticulate evolution due to hybridization and/or incomplete lineage sorting likely both contribute to gene-tree discordance. Morphological characters used to define taxa in current classification schemes are homoplastic in the ancestral character-state reconstructions. While target enrichment data allows us to broaden our understanding of diversification in Brunellia, the relationships among subclades remain incompletely understood.

Comparative analysis of complete Ilex (Aquifoliaceae) chloroplast genomes: insights into evolutionary dynamics and phylogenetic relationships

BACKGROUND

Ilex (Aquifoliaceae) are of great horticultural importance throughout the world for their foliage and decorative berries, yet a dearth of genetic information has hampered our understanding of phylogenetic relationships and evolutionary history. Here, we compare chloroplast genomes from across Ilex and estimate phylogenetic relationships.

RESULTS

We sequenced the chloroplast genomes of seven Ilex species and compared them with 34 previously published Ilex plastomes. The length of the seven newly sequenced Ilex chloroplast genomes ranged from 157,182 bp to 158,009 bp, and contained a total of 118 genes, including 83 protein-coding, 31 rRNA, and four tRNA genes. GC content ranged from 37.6 to 37.69%. Comparative analysis showed shared genomic structures and gene rearrangements. Expansion and contraction of the inverted repeat regions at the LSC/IRa and IRa/SSC junctions were observed in 22 and 26 taxa, respectively; in contrast, the IRb boundary was largely invariant. A total of 2146 simple sequence repeats and 2843 large repeats were detected in the 41 Ilex plastomes. Additionally, six genes (psaC, rbcL, trnQ, trnR, trnT, and ycf1) and two intergenic spacer regions (ndhC-trnV and petN-psbM) were identified as hypervariable, and thus potentially useful for future phylogenetic studies and DNA barcoding. We recovered consistent phylogenetic relationships regardless of inference methodology or choice of loci. We recovered five distinct, major clades, which were inconsistent with traditional taxonomic systems.

CONCLUSION

Our findings challenge traditional circumscriptions of the genus Ilex and provide new insights into the evolutionary history of this important clade. Furthermore, we detail hypervariable and repetitive regions that will be useful for future phylogenetic and population genetic studies.

Plastome phylogenomics and historical biogeography of aquatic plant genus Hydrocharis (Hydrocharitaceae)

BACKGROUND

Hydrocharis L. and Limnobium Rich. are small aquatic genera, including three and two species, respectively. The taxonomic status, phylogenetic relationships and biogeographical history of these genera have remained unclear, owing to the lack of Central African endemic H. chevalieri from all previous studies. We sequenced and assembled plastomes of all three Hydrocharis species and Limnobium laevigatum to explore the phylogenetic and biogeographical history of these aquatic plants.

RESULTS

All four newly generated plastomes were conserved in genome structure, gene content, and gene order. However, they differed in size, the number of repeat sequences, and inverted repeat borders. Our phylogenomic analyses recovered non-monophyletic Hydrocharis. The African species H. chevalieri was fully supported as sister to the rest of the species, and L. laevigatum was nested in Hydrocharis as a sister to H. dubia. Hydrocharis-Limnobium initially diverged from the remaining genera at ca. 53.3 Ma, then began to diversify at ca. 30.9 Ma. The biogeographic analysis suggested that Hydrocharis probably originated in Europe and Central Africa.

CONCLUSION

Based on the phylogenetic results, morphological similarity and small size of the genera, the most reasonable taxonomic solution to the non-monophyly of Hydrocharis is to treat Limnobium as its synonym. The African endemic H. chevalieri is fully supported as a sister to the remaining species. Hydrocharis mainly diversified in the Miocene, during which rapid climate change may have contributed to the speciation and extinctions. The American species of former Limnobium probably dispersed to America through the Bering Land Bridge during the Miocene.