Are differences in genomic data sets due to true biological variants or errors in genome assembly: an example from two chloroplast genomes

The complete chloroplast genome sequence of Eugenia klotzschiana O. Berg unveils the evolutionary dynamics in plastomes of Myrteae DC. tribe (Myrtaceae)

Myrteae is the most diversified tribe in the Myrtaceae family and has great ecological and economic importance. Here, we performed the assembly and annotation of the chloroplast genome of Eugenia klotzschiana O. Berg and used this in a comparative analysis with other 13 species from the Myrteae tribe. The E. klotzschiana plastome exhibited a length of 158,977 bp and a very conserved structure and gene composition when compared with other Myrteae genomes. We identified 34 large repetitive sequences and 94 SSR repeats in E. klotzschiana plastome. The trnT-trnL, rpl32-trnL, ndhF-rpl32, psbE-petL, and ycf1 regions were identified as mutational hotspots. A negative selection signal was detected in 74 protein-coding genes while neutral selection was detected in two genes (rps12 and psaI). Furthermore, 222 RNA editing sites were identified in the E. klotzschiana plastome. We also obtained a plastome-based Myrtales phylogenetic tree, including E. klotzschiana for the first time in a molecular phylogeny, recovering its sister relationship for all other Eugenia species. Our results illuminate how evolution shaped the chloroplast genome structure and composition in the Myrteae tribe, especially in the E. klotzschiana plastome.

Comparative plastome genomics, taxonomic delimitation and evolutionary divergences of Tetraena hamiensis var. qatarensis and Tetraena simplex (Zygophyllaceae)

The Zygophyllum and Tetraena genera are intriguingly important ecologically and medicinally. Based on morphological characteristics, T. hamiensis var. qatarensis, and T. simplex were transferred from Zygophyllum to Tetraena with the least genomic datasets available. Hence, we sequenced the T. hamiensis and T. simplex and performed in-depth comparative genomics, phylogenetic analysis, and estimated time divergences. The complete plastomes ranged between 106,720 and 106,446 bp-typically smaller than angiosperms plastomes. The plastome circular genomes are divided into large single-copy regions (~ 80,964 bp), small single-copy regions (~ 17,416 bp), and two inverted repeats regions (~ 4170 bp) in both Tetraena species. An unusual shrinkage of IR regions 16-24 kb was identified. This resulted in the loss of 16 genes, including 11 ndh genes which encode the NADH dehydrogenase subunits, and a significant size reduction of Tetraena plastomes compared to other angiosperms. The inter-species variations and similarities were identified using genome-wide comparisons. Phylogenetic trees generated by analyzing the whole plastomes, protein-coding genes, matK, rbcL, and cssA genes exhibited identical topologies, indicating that both species are sisters to the genus Tetraena and may not belong to Zygophyllum. Similarly, based on the entire plastome and proteins coding genes datasets, the time divergence of Zygophyllum and Tetraena was 36.6 Ma and 34.4 Ma, respectively. Tetraena stem ages were 31.7 and 18.2 Ma based on full plastome and protein-coding genes. The current study presents the plastome as a distinguishing and identification feature among the closely related Tetraena and Zygophyllum species. It can be potentially used as a universal super-barcode for identifying plants.

Comparative Analysis of Whole Chloroplast Genomes of Three Common Species of Echinochloa (Gramineae) in Paddy Fields

Echinochloa crus-galli var. crus-galli, E. crus-galli var. zelayensis, and E. glabrescens, morphologically similar at the seedling stage, are the most pernicious barnyard grass species in paddy fields worldwide. Chloroplast (cp) genomes could be conducive to their identification. In this study, we assembled the complete cp genome sequences of Echinochloa crus-galli var. crus-galli (139,856 bp), E. crus-galli var. zelayensis (139,874 bp), and E. glabrescens (139,874 bp), which exhibited a typical circular tetramerous structure, large and small single-copy regions, and a pair of inverted repeats. In Echinochloa crus-galli var. crus-galli, there were 136 simple sequence (SSRs) and 62 long (LRs) repeats, and in the other two species, 139 SSRs and 68 LRs. Each cp genome contains 92 protein-encoding genes. In Echinochloa crus-galli var. crus-galli and E. glabrescens, 321 and 1 single-nucleotide polymorphisms were detected compared to Echinochloa crus-galli var. zelayensis. IR expansion and contraction revealed small differences between the three species. The phylogenetic tree based on cp genomes demonstrated the phylogenetic relationship between ten barnyard grass species and other common Gramineae plants, showing new genetic relationships of the genus Echinochloa. This study provides valuable information on cp genomes, useful for identifying and classifying the genus Echinochloa and studying its phylogenetic relationships and evolution.

Software Choice and Sequencing Coverage Can Impact Plastid Genome Assembly-A Case Study in the Narrow Endemic Calligonum bakuense

Most plastid genome sequences are assembled from short-read whole-genome sequencing data, yet the impact that sequencing coverage and the choice of assembly software can have on the accuracy of the resulting assemblies is poorly understood. In this study, we test the impact of both factors on plastid genome assembly in the threatened and rare endemic shrub Calligonum bakuense. We aim to characterize the differences across plastid genome assemblies generated by different assembly software tools and levels of sequencing coverage and to determine if these differences are large enough to affect the phylogenetic position inferred for C. bakuense compared to congeners. Four assembly software tools (FastPlast, GetOrganelle, IOGA, and NOVOPlasty) and seven levels of sequencing coverage across the plastid genome (original sequencing depth, 2,000x, 1,000x, 500x, 250x, 100x, and 50x) are compared in our analyses. The resulting assemblies are evaluated with regard to reproducibility, contig number, gene complement, inverted repeat length, and computation time; the impact of sequence differences on phylogenetic reconstruction is assessed. Our results show that software choice can have a considerable impact on the accuracy and reproducibility of plastid genome assembly and that GetOrganelle produces the most consistent assemblies for C. bakuense. Moreover, we demonstrate that a sequencing coverage between 500x and 100x can reduce both the sequence variability across assembly contigs and computation time. When comparing the most reliable plastid genome assemblies of C. bakuense, a sequence difference in only three nucleotide positions is detected, which is less than the difference potentially introduced through software choice.

Chloroplast genomes in Populus (Salicaceae): comparisons from an intensively sampled genus reveal dynamic patterns of evolution

The chloroplast is one of two organelles containing a separate genome that codes for essential and distinct cellular functions such as photosynthesis. Given the importance of chloroplasts in plant metabolism, the genomic architecture and gene content have been strongly conserved through long periods of time and as such are useful molecular tools for evolutionary inferences. At present, complete chloroplast genomes from over 4000 species have been deposited into publicly accessible databases. Despite the large number of complete chloroplast genomes, comprehensive analyses regarding genome architecture and gene content have not been conducted for many lineages with complete species sampling. In this study, we employed the genus Populus to assess how more comprehensively sampled chloroplast genome analyses can be used in understanding chloroplast evolution in a broadly studied lineage of angiosperms. We conducted comparative analyses across Populus in order to elucidate variation in key genome features such as genome size, gene number, gene content, repeat type and number, SSR (Simple Sequence Repeat) abundance, and boundary positioning between the four main units of the genome. We found that some genome annotations were variable across the genus owing in part from errors in assembly or data checking and from this provided corrected annotations. We also employed complete chloroplast genomes for phylogenetic analyses including the dating of divergence times throughout the genus. Lastly, we utilized re-sequencing data to describe the variations of pan-chloroplast genomes at the population level for P. euphratica. The analyses used in this paper provide a blueprint for the types of analyses that can be conducted with publicly available chloroplast genomes as well as methods for building upon existing datasets to improve evolutionary inference.

Comparative chloroplast genomes and phylogenetic analysis of Aquilegia

PREMISE

Aquilegia is an ideal taxon for studying the evolution of adaptive radiation. Current phylogenies of Aquilegia based on different molecular markers are inconsistent, and therefore a clear and accurate phylogeny remains uncertain. Analyzing the chloroplast genome, with its simple structure and low recombination rate, may help solve this problem.

METHODS

Next-generation sequencing data were generated or downloaded for Aquilegia species, enabling their chloroplast genomes to be assembled. The assemblies were used to estimate the genome characteristics and infer the phylogeny of Aquilegia.

RESULTS

In this study, chloroplast genome sequences were assembled for Aquilegia species distributed across Asia, North America, and Europe. Three of the genes analyzed (petG, rpl36, and atpB) were shown to be under positive selection and may be related to adaptation. The phylogenetic tree of Aquilegia showed that its member species formed two clades with high support, North American and European species, with the Asian species being paraphyletic; A. parviflora and A. amurensis clustered with the North American species, while the remaining Asian species were found in the European clade. In addition, A. oxysepala var. kansuensis should be considered as a separate species rather than a variety.

DISCUSSION

The complete chloroplast genomes of these Aquilegia species provide new insights into the reconstruction of the phylogeny of related species and contribute to the further study of this genus.

Mangrove tree (Avicennia marina): insight into chloroplast genome evolutionary divergence and its comparison with related species from family Acanthaceae

Avicennia marina (family Acanthaceae) is a halotolerant woody shrub that grows wildly and cultivated in the coastal regions. Despite its importance, the species suffers from lack of genomic datasets to improve its taxonomy and phylogenetic placement across the related species. Here, we have aimed to sequence the plastid genome of A. marina and its comparison with related species in family Acanthaceae. Detailed next-generation sequencing and analysis showed a complete chloroplast genome of 150,279 bp, comprising 38.6% GC. Genome architecture is quadripartite revealing large single copy (82,522 bp), small single copy (17,523 bp), and pair of inverted repeats (25,117 bp). Furthermore, the genome contains 132 different genes, including 87 protein-coding genes, 8 rRNA, 37 tRNA genes, and 126 simple sequence repeats (122 mononucleotide, 2 dinucleotides, and 2 trinucleotides). Interestingly, about 25 forward, 15 reversed and 14 palindromic repeats were also found in the A. marina. High degree synteny was observed in the pairwise alignment with related genomes. The chloroplast genome comparative assessment showed a high degree of sequence similarity in coding regions and varying divergence in the intergenic spacers among ten Acanthaceae species. The pairwise distance showed that A. marina exhibited the highest divergence (0.084) with Justicia flava and showed lowest divergence with Aphelandra knappiae (0.059). Current genomic datasets are a valuable resource for investigating the population and evolutionary genetics of family Acanthaceae members' specifically A. marina and related species.

Comparative Analyses of Five Complete Chloroplast Genomes from the Genus Pterocarpus (Fabacaeae)

Pterocarpus is a genus of trees mainly distributed in tropical Asia, Africa, and South America. Some species of Pterocarpus are rosewood tree species, having important economic value for timber, and for some species, medicinal value as well. Up to now, information about this genus with regard to the genomic characteristics of the chloroplasts has been limited. Based on a combination of next-generation sequencing (Illumina Hiseq) and long-read sequencing (PacBio), the whole chloroplast genomes (cp genomes) of five species (rosewoods) in Pterocarpus (Pterocarpus macrocarpus, P. santalinus, P. indicus, P. pedatus, P. marsupium) have been assembled. The cp genomes of five species in Pterocarpus have similar structural characteristics, gene content, and sequence to other flowering plants. The cp genomes have a typical four-part structure, containing 110 unique genes (77 protein coding genes, 4 rRNAs, 29 tRNAs). Through comparative genomic analysis, abundant simple sequence repeat (SSR)loci (333-349) were detected in Pterocarpus, among which A /T single nucleotide repeats accounted for the highest proportion (72.8-76.4%). In the five cp genomes of Pterocarpus, eight hypervariable regions, including trnH-GUG_psbA, trnS-UGA_psbC, accD-psaI, ndhI-exon2_ndhI-exon1, ndhG_ndhi-exon2, rpoC2-exon2, ccsA, and trnfM-CAU, are proposed for use as DNA barcode regions. In the comparison of gene selection pressures (P. santalinus as the reference genome), purifying selection was inferred as the primary mode of selection in maintaining important biological functions. Phylogenetic analysis shows that Pterocarpus is a monophyletic group. The species P. tinctorius is resolved as early diverging in the genus. Pterocarpus was resolved as sister to the genus Tipuana.

PACVr: plastome assembly coverage visualization in R

BACKGROUND

Plastid genomes typically display a circular, quadripartite structure with two inverted repeat regions, which challenges automatic assembly procedures. The correct assembly of plastid genomes is a prerequisite for the validity of subsequent analyses on genome structure and evolution. The average coverage depth of a genome assembly is often used as an indicator of assembly quality. Visualizing coverage depth across a draft genome is a critical step, which allows users to inspect the quality of the assembly and, where applicable, identify regions of reduced assembly confidence. Despite the interplay between genome structure and assembly quality, no contemporary, user-friendly software tool can visualize the coverage depth of a plastid genome assembly while taking its quadripartite genome structure into account. A software tool is needed that fills this void.

RESULTS

We introduce 'PACVr', an R package that visualizes the coverage depth of a plastid genome assembly in relation to the circular, quadripartite structure of the genome as well as the individual plastome genes. By using a variable window approach, the tool allows visualizations on different calculation scales. It also confirms sequence equality of, as well as visualizes gene synteny between, the inverted repeat regions of the input genome. As a tool for plastid genomics, PACVr provides the functionality to identify regions of coverage depth above or below user-defined threshold values and helps to identify non-identical IR regions. To allow easy integration into bioinformatic workflows, PACVr can be invoked from a Unix shell, facilitating its use in automated quality control. We illustrate the application of PACVr on four empirical datasets and compare visualizations generated by PACVr with those of alternative software tools.

CONCLUSIONS

PACVr provides a user-friendly tool to visualize (a) the coverage depth of a plastid genome assembly on a circular, quadripartite plastome map and in relation to individual plastome genes, and (b) gene synteny across the inverted repeat regions. It contributes to optimizing plastid genome assemblies and increasing the reliability of publicly available plastome sequences. The software, example datasets, technical documentation, and a tutorial are available with the package at https://cran.r-project.org/package=PACVr.

Expanded inverted repeat region with large scale inversion in the first complete plastid genome sequence of Plantago ovata

Plantago ovata (Plantaginaceae) is an economically and medicinally important species, however, least is known about its genomics and evolution. Here, we report the first complete plastome genome of P. ovata and comparison with previously published genomes of related species from Plantaginaceae. The results revealed that P. ovata plastome size was 162,116 bp and that it had typical quadripartite structure containing a large single copy region of 82,084 bp and small single copy region of 5,272 bp. The genome has a markedly higher inverted repeat (IR) size of 37.4 kb, suggesting large-scale inversion of 13.8 kb within the expanded IR regions. In addition, the P. ovata plastome contains 149 different genes, including 43 tRNA, 8 rRNA, and 98 protein-coding genes. The analysis revealed 139 microsatellites, of which 71 were in the non-coding regions. Approximately 32 forward, 34 tandem, and 17 palindromic repeats were detected. The complete genome sequences, 72 shared genes, matK gene, and rbcL gene from related species generated the same phylogenetic signals, and phylogenetic analysis revealed that P. ovata formed a single clade with P. maritima and P. media. The divergence time estimation as employed in BEAST revealed that P. ovata diverged from P. maritima and P. media about 11.0 million years ago (Mya; 95% highest posterior density, 10.06-12.25 Mya). In conclusion, P. ovata had significant variation in the IR region, suggesting a more stable P. ovata plastome genome than that of other Plantaginaceae species.

Comparative Chloroplast Genomics of Endangered Euphorbia Species: Insights into Hotspot Divergence, Repetitive Sequence Variation, and Phylogeny

Euphorbia is one of the largest genera in the Euphorbiaceae family, comprising 2000 species possessing commercial, medicinal, and ornamental importance. However, there are very little data available on their molecular phylogeny and genomics, and uncertainties still exist at a taxonomic level. Herein, we sequence the complete chloroplast (cp) genomes of two species, E. larica and E. smithii, of the genus Euphorbia through next-generation sequencing and perform a comparative analysis with nine related genomes in the family. The results revealed that the cp genomes had similar quadripartite structure, gene content, and genome organization with previously reported genomes from the same family. The size of cp genomes ranged from 162,172 to 162,358 bp with 132 and 133 genes, 8 rRNAs, 39 tRNA in E. smithii and E. larica, respectively. The numbers of protein-coding genes were 85 and 86, with each containing 19 introns. The four-junction regions were studied and results reveal that rps19 was present at J_LB (large single copy region and inverted repeat b junction) in E. larica where its complete presence was located in the IRb (inverted repeat b) region in E. smithii. The sequence comparison revealed that highly divergent regions in rpoC1, rpocB, ycf3, clpP, petD, ycf1, and ndhF of the cp genomes might provide better understanding of phylogenetic inferences in the Euphorbiaceae and order Malpighiales. Phylogenetic analyses of this study illustrate sister clades of E. smithii with E. tricullii and these species form a monophyletic clade with E. larica. The current study might help us to understand the genome architecture, genetic diversity among populations, and evolutionary depiction in the genera.

Complete Chloroplast Genomes of Vachellia nilotica and Senegalia senegal: Comparative Genomics and Phylogenomic Placement in a New Generic System

Vachellia and Senegalia are the most important genera in the subfamily Mimosoideae (Fabaceae). Recently, species from both genera were separated from the long-characterized Acacia due to their macro-morphological characteristics. However, this morpho-taxonomic differentiation struggles to discriminate some species, for example, Vachellia nilotica and Senegalia senegal. Therefore, sequencing the chloroplast (cp) genomes of these species and determining their phylogenetic placement via conserved genes may help to validate the taxonomy. Hence, we sequenced the cp genomes of V. nilotica and S. senegal, and the results showed that the sizes of the genomes are 165.3 and 162.7 kb, respectively. The cp genomes of both species comprised large single-copy regions (93,849~91,791 bp) and pairs of inverted repeats (IR; 26,093~26,008 bp). The total numbers of genes found in the V. nilotica and S. senegal cp genomes were 135 and 132, respectively. Approximately 123:130 repeats and 290:281 simple sequence repeats were found in the S. senegal and V. nilotica cp genomes, respectively. Genomic characterization was undertaken by comparing these genomes with those of 17 species belonging to related genera in Fabaceae. A phylogenetic analysis of the whole genome dataset and 56 shared genes was undertaken by generating cladograms with the same topologies and placing both species in a new generic system. These results support the likelihood of identifying segregate genera from Acacia with phylogenomic disposition of both V. nilotica and S. senegal in the subfamily Mimosoideae. The current study is the first to obtain complete genomic information on both species and may help to elucidate the genome architecture of these species and evaluate the genetic diversity among species.

Comparative analyses of chloroplast genomes from 22 Lythraceae species: inferences for phylogenetic relationships and genome evolution within Myrtales

BACKGROUND

Lythraceae belongs to the order Myrtales, which is part of Archichlamydeae. The family has 31 genera containing approximately 620 species of herbs, shrubs and trees. Of these 31 genera, five large genera each possess 35 or more species. They are Lythrum, with 35; Rotala, with 45; Nesaea, with 50; Lagerstroemia, with 56; and Cuphea, with 275 species.

RESULTS

We reported six newly sequenced chloroplast (cp) genomes (Duabanga grandiflora, Trapa natans, Lythrum salicaria, Lawsonia inermis, Woodfordia fruticosa and Rotala rotundifolia) and compared them with 16 other cp genomes of Lythraceae species. The cp genomes of the 22 Lythraceae species ranged in length from 152,049 bp to 160,769 bp. In each Lythraceae species, the cp genome contained 112 genes consisting of 78 protein coding genes, four ribosomal RNAs and 30 transfer RNAs. Furthermore, we detected 211-332 simple sequence repeats (SSRs) in six categories and 7-27 long repeats in four categories. We selected ten divergent hotspots (ndhF, matK, ycf1, rpl22, rpl32, trnK-rps16, trnR-atpA, rpl32-trnL, trnH-psbA and trnG-trnR) among the 22 Lythraceae species to be potential molecular markers. We constructed phylogenetic trees from 42 Myrtales plants with 8 Geraniales plants as out groups. The relationships among the Myrtales species were effectively distinguished by maximum likelihood (ML), maximum parsimony (MP) and Bayesian inference (BI) trees constructed using 66 protein coding genes. Generally, the 22 Lythraceae species gathered into one clade, which was resolved as sister to the three Onagraceae species. Compared with Melastomataceae and Myrtaceae, Lythraceae and Onagraceae differentiated later within Myrtales.

CONCLUSIONS

The study provided ten potential molecular markers as candidate DNA barcodes and contributed cp genome resources within Myrtales for further study.

First complete chloroplast genomics and comparative phylogenetic analysis of Commiphora gileadensis and C. foliacea: Myrrh producing trees

Commiphora gileadensis and C. foliacea (family Burseraceae) are pantropical in nature and known for producing fragrant resin (myrrh). Both the tree species are economically and medicinally important however, least genomic understanding is available for this genus. Herein, we report the complete chloroplast genome sequences of C. gileadensis and C. foliacea and comparative analysis with related species (C. wightii and Boswellia sacra). A modified chloroplast DNA extraction method was adopted, followed with next generation sequencing, detailed bioinformatics and PCR analyses. The results revealed that the cp genome sizes of C. gileadensis and C. foliacea, are 160,268 and 160,249 bp, respectively, with classic quadripartite structures that comprises of inverted repeat's pair. Overall, the organization of these cp genomes, GC contents, gene order, and codon usage were comparable to other cp genomes in angiosperm. Approximately, 198 and 175 perfect simple sequence repeats were detected in C. gileadensis and C. foliacea genomes, respectively. Similarly, 30 and 25 palindromic, 15 and 25 forward, and 20 and 25 tandem repeats were determined in both the cp genomes, respectively. Comparison of these complete cp genomes with C. wightii and B. sacra revealed significant sequence resemblance and comparatively highest deviation in intergenic spacers. The phylo-genomic comparison showed that C. gileadensis and C. foliacea form a single clade with previously reported C. wightii and B. sacra from family Burseraceae. Current study reports for the first time the cp genomics of species from Commiphora, which could be helpful in understanding genetic diversity and phylogeny of this myrrh producing species.

First reported chloroplast genome sequence of Punica granatum (cultivar Helow) from Jabal Al-Akhdar, Oman: phylogenetic comparative assortment with Lagerstroemia

Pomegranate (Punica granatum L.) is one of the oldest known edible fruits. It has grown in popularity and is a profitable fruit crop due to its attractive features including a bright red appearance and its biological activities. Scientific exploration of the genetics and evolution of these beneficial traits has been hampered by limited genomic information. In this study, we sequenced the complete chloroplast (cp) genome of the native P. granatum (cultivar Helow) cultivated in the mountains of Jabal Al-Akhdar, Oman. The results revealed a P. granatum cp genome length of 158,630 bp, characterized by a relatively conserved structure containing 2 inverted repeat regions of 25,466 bp, an 18,686 bp small single copy regions, and an 89,015 bp large single copy region. The 86 protein-coding genes included 37 transfer RNA genes and 8 ribosomal RNA genes. Comparison of the P. granatum whole cp genome with seven Lagerstroemia species revealed an overall high degree of sequence similarity with divergence among intergenic spacers. The location, distribution, and divergence of repeat sequences and shared genes of the Punica and Lagerstroemia species were highly similar. Analyses of nucleotide substitution, insertion/deletions, and highly variable regions in these cp genomes identified potential plastid markers for taxonomic and phylogenetic studies in Myrtales. A phylogenetic study of the cp genomes and 76 shared coding regions generated similar cladograms. The complete cp genome of P. granatum will aid in taxonomical studies of the family Lythraceae.

First chloroplast genomics study of Phoenix dactylifera (var. Naghal and Khanezi): A comparative analysis

Date palm (Phoenix dactylifera L.) is one of the oldest fruit crops in the arid regions of the Middle East. However, little information is available regarding its plastid genomes. In this study, we sequenced the chloroplast (cp) genomes of two economically important but genomically unexplored date palm cultivars of Phoenix dactylifera (var. Naghal and Khanezi). The data assembly and genome annotation revealed a typical quadripartite structure similar to Arecaceae, and the genome sizes of Naghal and Khanezi were 158,210 bp and 158,211 bp, respectively. Structurally, both cp genomes were comprised of four regions: a pair of inverted repeats (27,273 bp for Khanezi and for Naghal 27,272 bp), a large single-copy region (86,090 bp and 86,092 bp) and a small single-copy region (17,575 bp and 17,574 bp). Both genomes had 138 representative genes, whereas 227 and 229 randomly distributed microsatellites were also observed in Khanezi and Naghal, respectively. Phylogenetic analysis based on the whole cp genomes and 68 shared genes showed identical phylogenetic trees of Khanezi and Naghal forming clades with Khalas and Aseel cultivars, respectively. The current study showed detailed comparative cp genome analysis, which could be essential for broader population genetics and molecular studies of these four date palm cultivars.

The Complete Chloroplast Genome of Heimia myrtifolia and Comparative Analysis within Myrtales

Heimia myrtifolia is an important medicinal plant with several pharmacologically active alkaloids and is also used as an ornamental landscape plant. The purpose of this study is to complete and characterize the chloroplast (cp) genome of H. myrtifolia and compare genomic features to other Myrtales species' cp genomes. The analysis showed that H. myrtifolia has a total length of 159,219 bp with a typical quadripartite structure containing two identical inverted repeats (IRs) of 25,643 bp isolated by one large single copy (LSC) of 88,571 bp and one small single copy (SSC) of 18,822 bp. The H. myrtifolia cp genome contains 129 genes with eight ribosomal RNAs, 30 transfer RNAs, and 78 protein coding genes, in which 17 genes are duplicated in two IR regions. The genome organization including gene type and number and guanine-cytosine (GC) content is analyzed among the 12 cp genomes in this study. Approximately 255 simple sequence repeats (SSRs) and 16 forward, two reverses, and two palindromic repeats were identified in the H. myrtifolia cp genome. By comparing the whole H. myrtifolia cp genome with 11 other Myrtales species, the results showed that the sequence similarity was high between coding regions while sequence divergence was high between intergenic regions. By employing the full cp genomes for phylogenetic analysis, structural and sequence differences were characterized between H. myrtifolia and 11 Myrtales species illustrating what patterns are common in the evolution of cp genomes within the Myrtales. The first entire cp genome in the genus Heimia provides a valuable resource for further studies in these medicinally and ornamentally important taxa.

Complete chloroplast genome sequence and comparative analysis of loblolly pine (Pinus taeda L.) with related species

Pinaceae, the largest family of conifers, has a diversified organization of chloroplast (cp) genomes with two typical highly reduced inverted repeats (IRs). In the current study, we determined the complete sequence of the cp genome of an economically and ecologically important conifer tree, the loblolly pine (Pinus taeda L.), using Illumina paired-end sequencing and compared the sequence with those of other pine species. The results revealed a genome size of 121,531 base pairs (bp) containing a pair of 830-bp IR regions, distinguished by a small single copy (42,258 bp) and large single copy (77,614 bp) region. The chloroplast genome of P. taeda encodes 120 genes, comprising 81 protein-coding genes, four ribosomal RNA genes, and 35 tRNA genes, with 151 randomly distributed microsatellites. Approximately 6 palindromic, 34 forward, and 22 tandem repeats were found in the P. taeda cp genome. Whole cp genome comparison with those of other Pinus species exhibited an overall high degree of sequence similarity, with some divergence in intergenic spacers. Higher and lower numbers of indels and single-nucleotide polymorphism substitutions were observed relative to P. contorta and P. monophylla, respectively. Phylogenomic analyses based on the complete genome sequence revealed that 60 shared genes generated trees with the same topologies, and P. taeda was closely related to P. contorta in the subgenus Pinus. Thus, the complete P. taeda genome provided valuable resources for population and evolutionary studies of gymnosperms and can be used to identify related species.

The Complete Chloroplast Genome of Catha edulis: A Comparative Analysis of Genome Features with Related Species

Qat (Catha edulis, Celastraceae) is a woody evergreen species with great economic and cultural importance. It is cultivated for its stimulant alkaloids cathine and cathinone in East Africa and southwest Arabia. However, genome information, especially DNA sequence resources, for C. edulis are limited, hindering studies regarding interspecific and intraspecific relationships. Herein, the complete chloroplast (cp) genome of Catha edulis is reported. This genome is 157,960 bp in length with 37% GC content and is structurally arranged into two 26,577 bp inverted repeats and two single-copy areas. The size of the small single-copy and the large single-copy regions were 18,491 bp and 86,315 bp, respectively. The C. edulis cp genome consists of 129 coding genes including 37 transfer RNA (tRNA) genes, 8 ribosomal RNA (rRNA) genes, and 84 protein coding genes. For those genes, 112 are single copy genes and 17 genes are duplicated in two inverted regions with seven tRNAs, four rRNAs, and six protein coding genes. The phylogenetic relationships resolved from the cp genome of qat and 32 other species confirms the monophyly of Celastraceae. The cp genomes of C. edulis, Euonymus japonicus and seven Celastraceae species lack the rps16 intron, which indicates an intron loss took place among an ancestor of this family. The cp genome of C. edulis provides a highly valuable genetic resource for further phylogenomic research, barcoding and cp transformation in Celastraceae.

Chloroplast genomes of Arabidopsis halleri ssp. gemmifera and Arabidopsis lyrata ssp. petraea: Structures and comparative analysis

We investigated the complete chloroplast (cp) genomes of non-model Arabidopsis halleri ssp. gemmifera and Arabidopsis lyrata ssp. petraea using Illumina paired-end sequencing to understand their genetic organization and structure. Detailed bioinformatics analysis revealed genome sizes of both subspecies ranging between 154.4~154.5 kbp, with a large single-copy region (84,197~84,158 bp), a small single-copy region (17,738~17,813 bp) and pair of inverted repeats (IRa/IRb; 26,264~26,259 bp). Both cp genomes encode 130 genes, including 85 protein-coding genes, eight ribosomal RNA genes and 37 transfer RNA genes. Whole cp genome comparison of A. halleri ssp. gemmifera and A. lyrata ssp. petraea, along with ten other Arabidopsis species, showed an overall high degree of sequence similarity, with divergence among some intergenic spacers. The location and distribution of repeat sequences were determined, and sequence divergences of shared genes were calculated among related species. Comparative phylogenetic analysis of the entire genomic data set and 70 shared genes between both cp genomes confirmed the previous phylogeny and generated phylogenetic trees with the same topologies. The sister species of A. halleri ssp. gemmifera is A. umezawana, whereas the closest relative of A. lyrata spp. petraea is A. arenicola.

Comparative analysis of complete plastid genomes from wild soybean (Glycine soja) and nine other Glycine species

The plastid genomes of different plant species exhibit significant variation, thereby providing valuable markers for exploring evolutionary relationships and population genetics. Glycine soja (wild soybean) is recognized as the wild ancestor of cultivated soybean (G. max), representing a valuable genetic resource for soybean breeding programmes. In the present study, the complete plastid genome of G. soja was sequenced using Illumina paired-end sequencing and then compared it for the first time with previously reported plastid genome sequences from nine other Glycine species. The G. soja plastid genome was 152,224 bp in length and possessed a typical quadripartite structure, consisting of a pair of inverted repeats (IRa/IRb; 25,574 bp) separated by small (178,963 bp) and large (83,181 bp) single-copy regions, with a 51-kb inversion in the large single-copy region. The genome encoded 134 genes, including 87 protein-coding genes, eight ribosomal RNA genes, and 39 transfer RNA genes, and possessed 204 randomly distributed microsatellites, including 15 forward, 25 tandem, and 34 palindromic repeats. Whole-plastid genome comparisons revealed an overall high degree of sequence similarity between G. max and G. gracilis and some divergence in the intergenic spacers of other species. Greater numbers of indels and SNP substitutions were observed compared with G. cyrtoloba. The sequence of the accD gene from G. soja was highly divergent from those of the other species except for G. max and G. gracilis. Phylogenomic analyses of the complete plastid genomes and 76 shared genes yielded an identical topology and indicated that G. soja is closely related to G. max and G. gracilis. The complete G. soja genome sequenced in the present study is a valuable resource for investigating the population and evolutionary genetics of Glycine species and can be used to identify related species.

Characterization of the whole chloroplast genome of Chikusichloa mutica and its comparison with other rice tribe (Oryzeae) species

Chloroplast genomes are a significant genomic resource in plant species and have been used in many research areas. The complete genomic information from wild crop species could supply a valuable genetic reservoir for breeding. Chikusichloa mutica is one of the most important wild distant relatives of cultivated rice. In this study, we sequenced and characterized its complete chloroplast (cp) genome and compared it with other species in the same tribe. The whole cp genome sequence is 136,603 bp in size and exhibits a typical quadripartite structure with large and small single-copy regions (LSC, 82,327 bp; SSC, 12,598 bp) separated by a pair of 20,839-bp inverted repeats (IRA, B). A total of 110 unique genes are annotated, including 76 protein-coding genes, 4 ribosomal RNA genes and 30 tRNA genes. The genome structure, gene order, GC content, and other features are similar to those of other angiosperm cp genomes. When comparing the cp genomes between Oryzinae and Zizaniinae subtribes, the main differences were found between the junction regions and distribution of simple sequence repeats (SSRs). In comparing the two Chikusichloa species, the genomes were only 40 bp different in length and 108 polymorphic sites, including 83 single nucleotide substitutions (SNPs) and 25 insertion-deletions (Indels), were found between the whole cp genomes. The complete cp genome of C. mutica will be an important genetic tool for future breeding programs and understanding the evolution of wild rice relatives.

The Complete Chloroplast Genome of Wild Rice (Oryza minuta) and Its Comparison to Related Species

Oryza minuta, a tetraploid wild relative of cultivated rice (family Poaceae), possesses a BBCC genome and contains genes that confer resistance to bacterial blight (BB) and white-backed (WBPH) and brown (BPH) plant hoppers. Based on the importance of this wild species, this study aimed to understand the phylogenetic relationships of O. minuta with other Oryza species through an in-depth analysis of the composition and diversity of the chloroplast (cp) genome. The analysis revealed a cp genome size of 135,094 bp with a typical quadripartite structure and consisting of a pair of inverted repeats separated by small and large single copies, 139 representative genes, and 419 randomly distributed microsatellites. The genomic organization, gene order, GC content and codon usage are similar to those of typical angiosperm cp genomes. Approximately 30 forward, 28 tandem and 20 palindromic repeats were detected in the O. minuta cp genome. Comparison of the complete O. minuta cp genome with another eleven Oryza species showed a high degree of sequence similarity and relatively high divergence of intergenic spacers. Phylogenetic analyses were conducted based on the complete genome sequence, 65 shared genes and matK gene showed same topologies and O. minuta forms a single clade with parental O. punctata. Thus, the complete O. minuta cp genome provides interesting insights and valuable information that can be used to identify related species and reconstruct its phylogeny.

The complete chloroplast genome of queen's crape-myrtle(Lagerstroemia macrocarpa)

The whole complete chloroplast genome of Lagerstroemia macrocarpa was assembled in this study. Total genome is 152,472 bp in length consisting of two inverted repeats of 17,562 bp separated by a large single-copy region and a small single-copy region of 84,050 bp and 33,295 bp, respectively. This genome contains 112 unique genes including 78 protein-coding genes, 4 ribosomal RNA genes and 30 transfer RNA genes. In 78 protein-coding genes, 8 genes (atpF, ndhA, ndhB, petB, petD, rpl16, rpoC1, rps16) contain one intron and three genes with two introns each (clpP, rps12 and ycf3). This newly sequenced chloroplast genome supply highly variable information of polymorphisms within Lagerstroemia species.

Chloroplast Genome Sequence of Lagerstroemia guilinensis (Lythraceae, Myrtales), a Species Endemic to the Guilin Limestone Area in Guangxi Province, China

We announce here the first complete chloroplast genome sequence of Lagerstroemia guilinensis (Lythraceae, Myrtales), a species endemic to the Guilin limestone area, along with its genome structure and functional gene annotations. The plant was collected from Guilin, Guangxi, China, and deposited as a germplasm accession of the Zhejiang Agriculture and Forestry University Collection (ZAFU 1507144). This genome will provide valuable information for future research of the Lagerstroemia genus and its relatives.

Use of microsatellite markers for the assessment of bambara groundnut breeding system and varietal purity before genome sequencing

Maximizing the research output from a limited investment is often the major challenge for minor and underutilized crops. However, such crops may be tolerant to biotic and abiotic stresses and are adapted to local, marginal, and low-input environments. Their development through breeding will provide an important resource for future agricultural system resilience and diversification in the context of changing climates and the need to achieve food security. The African Orphan Crops Consortium recognizes the values of genomic resources in facilitating the improvement of such crops. Prior to beginning genome sequencing there is a need for an assessment of line varietal purity and to estimate any residual heterozygosity. Here we present an example from bambara groundnut (Vigna subterranea (L.) Verdc.), an underutilized drought tolerant African legume. Two released varieties from Zimbabwe, identified as potential genotypes for whole genome sequencing (WGS), were genotyped with 20 species-specific SSR markers. The results indicate that the cultivars are actually a mix of related inbred genotypes, and the analysis allowed a strategy of single plant selection to be used to generate non-heterogeneous DNA for WGS. The markers also confirmed very low levels of heterozygosity within individual plants. The application of a pre-screen using co-dominant microsatellite markers is expected to substantially improve the genome assembly, compared to a cultivar bulking approach that could have been adopted.

The Complete Plastid Genome of Lagerstroemia fauriei and Loss of rpl2 Intron from Lagerstroemia (Lythraceae)

Lagerstroemia (crape myrtle) is an important plant genus used in ornamental horticulture in temperate regions worldwide. As such, numerous hybrids have been developed. However, DNA sequence resources and genome information for Lagerstroemia are limited, hindering evolutionary inferences regarding interspecific relationships. We report the complete plastid genome of Lagerstroemia fauriei. To our knowledge, this is the first reported whole plastid genome within Lythraceae. This genome is 152,440 bp in length with 38% GC content and consists of two single-copy regions separated by a pair of 25,793 bp inverted repeats. The large single copy and the small single copy regions span 83,921 bp and 16,933 bp, respectively. The genome contains 129 genes, including 17 located in each inverted repeat. Phylogenetic analysis of genera sampled from Geraniaceae, Myrtaceae, and Onagraceae corroborated the sister relationship between Lythraceae and Onagraceae. The plastid genomes of L. fauriei and several other Lythraceae species lack the rpl2 intron, which indicating an early loss of this intron within the Lythraceae lineage. The plastid genome of L. fauriei provides a much needed genetic resource for further phylogenetic research in Lagerstroemia and Lythraceae. Highly variable markers were identified for application in phylogenetic, barcoding and conservation genetic applications.

Complete Chloroplast Genome of Nicotiana otophora and its Comparison with Related Species

Nicotiana otophora is a wild parental species of Nicotiana tabacum, an interspecific hybrid of Nicotiana tomentosiformis and Nicotiana sylvestris. However, N. otophora is least understood as an alternative paternal donor. Here, we compared the fully assembled chloroplast (cp) genome of N. otophora and with those of closely related species. The analysis showed a cp genome size of 156,073 bp and exhibited a typical quadripartite structure, which contains a pair of inverted repeats separated by small and large single copies, containing 163 representative genes, with 165 microsatellites distributed unevenly throughout the genome. Comparative analysis of a gene with known function across Nicotiana species revealed 76 protein-coding sequences, 20 tRNA sequences, and 3 rRNA sequence shared between the cp genomes. The analysis revealed that N. otophora is a sister species to N. tomentosiformis within the Nicotiana genus, and Atropha belladonna and Datura stramonium are their closest relatives. These findings provide a valuable analysis of the complete N. otophora cp genome, which can identify species, elucidate taxonomy, and reconstruct the phylogeny of genus Nicotiana.

Two complete chloroplast genomes of white campion (Silene latifolia) from male and female individuals

In this study, we assembled two individuals' complete chloroplast genomes with one male and one female from the dioecious plant species white campion (Silene latifolia). The two chloroplast genomes have an identical composition with each other as a circular molecule of 150 931 bp in length, with an overall GC content of 36.4%. The genomes consist of a pair of inverted repeats (IRs) of 25 503 bp, separated by a large single-copy (LSC) region and a small single-copy (SSC) region of 82 708 and 17 217 bp, respectively. The genomes contain 111 single copy genes, including 77 protein-coding genes, 4 ribosomal RNA genes and 30 transfer RNA genes. In these protein-coding genes, eight genes (rpl16, rpoC1, rps16, petD, petB, ndhB, ndhA and atpF) contain a single intron and three genes (rps12, clpP and ycf3) contain two introns. The two newly sequenced chloroplast genomes provide valuable information for detecting polymorphisms within species and between sexes.

Infraspecific variation within and across complete organellar genomes and nuclear ribosomal repeats in a moss

Bryophytes (mosses, liverworts, and hornworts) are diverse and ecologically and evolutionarily significant yet genome scale data sets and analyses remain extremely sparse relative to other groups of plants, and are completely lacking at the infraspecific level. By sequencing the complete organellar genomes and nuclear ribosomal repeat from seven patches of a South American sub-Antarctic neo-endemic non-model moss, we present the first characterization of infraspecific polymorphism within and across the three genomic compartments for a bryophyte. Diversity within patches is accounted for by both intraindividual and interindividual variation for the nuclear ribosomal repeat and plastid genome, respectively. This represents the most extensive infraspecific genomic dataset generated for an early land plant lineage thus far and provides insight into relative rates of substitution between organellar genomes, including high rates of nonsynonymous to synonymous substitutions.

Limited variation across two chloroplast genomes with finishing chloroplast genome of Capsella grandiflora

The complete chloroplast genome of Capsella grandiflora is finished in this study, which consists of 154 638 base pairs (bp) in size containing a pair of inverted repeats (IRa and IRb) of 26 462 bp each and a small and large single-copies (SSC and LSC) of 17 835 and 83 879 bp, respectively. The overall GC content is 36.54% and the GC contents of LSC, IRs, and SSC are 34.34%, 42.38%, and 29.61% separately. The gene contents and numbers are the same with other two published species in genus Capsella with 112 annotated unique genes including 78 protein-coding genes, 30 tRNA genes, and four rRNA genes. Among these, 16 are duplicated in the inverted repeat regions, 15 genes contained one intron, and three genes (rps12, clpP, and ycf3) comprising two introns. Based on the whole genome comparison, only 28 SNPs and 16 Indels (insertion and deletion) are detected between two closed relatives' chloroplast genomes.

The complete chloroplast genome of Capsella rubella

The whole nucleotide sequence of the chloroplast genome from Capsella rubella is determined in this study using short Illumina sequence data from public database. The circular double-stranded DNA, which consists of 154,601 base pairs (bp) in size, contains a pair of inverted repeats (IRa and IRb) of 26,462 bp each, which are separated by a small and large single-copies (SSC and LSC) of 17,855 and 83,822 bp, respectively. The overall GC content of the chloroplast genome is 36.54% and the GC contents of LSC, IRs and SSC are 34.33%, 42.38% and 29.61% separately. One hundred and twelve unique genes were annotated, including 78 protein-coding genes, 30 tRNA genes and 4 rRNA genes. Among these, 16 are duplicated in the inverted repeat regions, 15 genes contained 1 intron, and 3 genes (rps12, clpP and ycf3) comprised of 2 introns. Two protein genes (rps19 and ycf1) span in the boundaries of LSC-IR and IR-SSC to produce two partial pseudogenes.