The Chloroplast Genome of Passiflora edulis (Passifloraceae) Assembled from Long Sequence Reads: Structural Organization and Phylogenomic Studies in Malpighiales

Phylogenetic placement of the monotypic Baolia (Amaranthaceae s.l.) based on morphological and molecular evidence

BACKGROUND

Baolia H.W.Kung & G.L.Chu is a monotypic genus only known in Diebu County, Gansu Province, China. Its systematic position is contradictory, and its morphoanatomical characters deviate from all other Chenopodiaceae. Recent study has regarded Baolia as a sister group to Corispermoideae. We therefore sequenced and compared the chloroplast genomes of this species, and resolved its phylogenetic position based on both chloroplast genomes and marker sequences.

RESULTS

We sequenced 18 chloroplast genomes of 16 samples from two populations of Baolia bracteata and two Corispermum species. These genomes of Baolia ranged in size from 152,499 to 152,508 bp. Simple sequence repeats (SSRs) were primarily located in the LSC region of Baolia chloroplast genomes, and most of them consisted of single nucleotide A/T repeat sequences. Notably, there were differences in the types and numbers of SSRs between the two populations of B. bracteata. Our phylogenetic analysis, based on both complete chloroplast genomes from 33 species and a combination of three markers (ITS, rbcL, and matK) from 91 species, revealed that Baolia and Corispermoideae (Agriophyllum, Anthochlamys, and Corispermum) form a well-supported clade and sister to Acroglochin. According to our molecular dating results, a major divergence event between Acroglochin, Baolia, and Corispermeae occurred during the Middle Eocene, approximately 44.49 mya. Ancestral state reconstruction analysis showed that Baolia exhibited symplesiomorphies with those found in core Corispermoideae characteristics including pericarp and seed coat.

CONCLUSIONS

Comparing the chloroplast genomes of B. bracteata with those of eleven typical Chenopodioideae and Corispermoideae species, we observed a high overall similarity and a one notable noteworthy case of inversion of approximately 3,100 bp. of DNA segments only in two Atriplex and four Chenopodium species. We suggest that Corispermoideae should be considered in a broader sense, it includes Corispermeae (core Corispermoideae: Agriophyllum, Anthochlamys, and Corispermum), as well as two new monotypic tribes, Acroglochineae (Acroglochin) and Baolieae (Baolia).

Comparative genomics and phylogenetic analysis of chloroplast genomes of Asian Caryodaphnopsis taxa (Lauraceae)

The genus Caryodaphnopsis, a member of the Lauraceae family, is characterized by seeds that are rich in oil, as well as highly exploitable fruits and wood. The Asian taxa within this genus exhibit complex morphological variations, posing challenges to their accurate classification and impeding their effective use and development as a resource. In this study, we sequenced the chloroplast genomes of 31 individuals representing nine Asian taxa within the Caryodaphnopsis genus. Our primary objectives were to reveal structural variations in these chloroplast genomes through comparative analyses and to infer the species' phylogenetic relationships. Our findings revealed that all chloroplast genomes had a tetrad structure, ranged in length from 148,828 to 154,946 bp, and harbored 128-131 genes. Notably, contraction of the IR region led to the absence of some genes in eight taxa. A comprehensive analysis identified 1267 long repetitive sequences and 2176 SSRs, 286 SNPs, and 135 indels across the 31 chloroplast genomes. The Ka/Ks ratio analysis indicated potential positive selection on the matK, rpl22, and rpoC2 genes. Furthermore, we identified six variable regions as promising barcode regions. Phylogenetic analysis grouped the nine Asian taxa into six branches, with C. henryi forming the basal group from which three distinct complexes emerged. This study contributes significantly to the current understanding of the evolutionary dynamics and phylogenetic relationships within the genus Caryodaphnopsis. Furthermore, the identified molecular markers hold potential for molecular barcoding applications in population genetics, providing valuable tools for future research and conservation efforts within this diverse genus.

Characterization of the complete chloroplast genome of Helicteres hirsuta Lour. 1790 (Helicteriodeae: Malvaceae)

Helicteres hirsuta Lour. 1790 is a precious medicinal plant species, especially for treating chronic liver diseases. Genomic data on H. hirsuta are limited. Therefore, this current study aimed to characterize the chloroplast genome of H. hirsuta and reconstruct the phylogenetic relationship among Helicteroideae taxa. Consequently, the complete chloroplast genome of H. hirsuta was 163,404 bp in length and contained 113 unique genes (79 protein-coding genes, 30 tRNA genes, and four rRNA genes). Notably, two introns of clpP gene of H. hirsuta were lost in comparison to that of other Helicteroideae species. The phylogenetic tree based on chloroplast genomes of eleven Helicteroideae species revealed that H. hirsuta was closely related to Reevesia species. In conclusion, our study described the first complete chloroplast genome of H. hirsuta, which is essential for tracing evolutionary history in the Helicteroideae subfamily.

The first complete chloroplast genome of Thalictrum fargesii: insights into phylogeny and species identification

Introduction

Thalictrum fargesii is a medicinal plant belonging to the genus Thalictrum of the Ranunculaceae family and has been used in herbal medicine in the Himalayan regions of China and India. This species is taxonomically challenging because of its morphological similarities to other species within the genus. Thus, herbal drugs from this species are frequently adulterated, substituted, or mixed with other species, thereby endangering consumer safety.

Methods

The present study aimed to sequence and assemble the entire chloroplast (cp) genome of T. fargesii using the Illumina HiSeq 2500 platform to better understand the genomic architecture, gene composition, and phylogenetic relationships within the Thalictrum.

Results and discussion

The cp genome was 155,929 bp long and contained large single-copy (85,395 bp) and small single-copy (17,576 bp) regions that were segregated by a pair of inverted repeat regions (26,479 bp) to form a quadripartite structure. The cp genome contains 133 genes, including 88 protein-coding genes (PCGs), 37 tRNA genes, and 8 rRNA genes. Additionally, this genome contains 64 codons that encode 20 amino acids, the most preferred of which are alanine and leucine. We identified 68 SSRs, 27 long repeats, and 242 high-confidence C-to-U RNA-editing sites in the cp genome. Moreover, we discovered seven divergent hotspot regions in the cp genome of T. fargesii, among which ndhD-psaC and rpl16-rps3 may be useful for developing molecular markers for identifying ethnodrug species and their contaminants. A comparative study with eight other species in the genus revealed that pafI and rps19 had highly variable sites in the cp genome of T. fargesii. Additionally, two special features, (i) the shortest length of the ycf1 gene at the IRA-SSC boundary and (ii) the distance between the rps19 fragment and trnH at the IRA-LSC junction, distinguish the cp genome of T. fargesii from those of other species within the genus. Furthermore, phylogenetic analysis revealed that T. fargesii was closely related to T. tenue and T. petaloidium.

Conclusion

Considering all these lines of evidence, our findings offer crucial molecular and evolutionary information that could play a significant role in further species identification, evolution, and phylogenetic studies on T. fargesii.

Chloroplast genomes in seven Lagerstroemia species provide new insights into molecular evolution of photosynthesis genes

Lagerstroemia indica is an important commercial tree known for the ornamental value. In this study, the complete chloroplast genome sequence of Lagerstroemia indica "Pink Velour" (Lagerstroemia "Pink Velour") was 152,174 bp in length with a GC content of 39.50%. It contained 85 protein coding genes (PCGs), 37 tRNAs, and 8 rRNA genes. 207 simple sequence repeats (SSRs) and 31 codons with relative synonymous codon (RSCU)value > 1 were detected. Phylogenetic analysis divided 10 Lagerstroemia species into evolutionary branches of clade A and clade B. We conducted a comparative analysis of Lagerstroemia "Pink Velours" complete chloroplast genome with the genomes of six closely related Lagerstroemia species from different origins. The structural features of all seven species were similar, except for the deletion of ycf1 nucleobases at the JSA boundary. The large single-copy (LSC) and the small single-copy (SSC) had a higher sequence divergence than the IR region, and 8 genes that were highly divergent (trnK-UUU, petN, psbF, psbJ, ndhE, ndhD, ndhI, ycf1) had been identified and could be used as molecular markers in future studies. High nucleotide diversity was present in genes belonging to the photosynthesis category. Mutation of single nucleic acid was mainly influenced by codon usage. The value percentage of nonsynonymous substitutions (Ka) and synonymous substitutions (Ks) in 6 Lagerstroemia species revealed that more photosynthesis genes have Ka or Ks only in Lagerstroemia fauriei, Lagerstroemia limii, and Lagerstroemia subcostata. These advances will facilitate the breeding of closely related Lagerstroemia species and deepen understanding on climatic adaptation of Lagerstroemia plants.

Plastid genome of Passiflora tripartita var. mollissima (poro-poro) from Huánuco, Peru

Passiflora tripartita var. mollissima, known locally as poro-poro, is an important native fruit used in traditional Peruvian medicine with relevant agro-industrial and pharmaceutical potential for its antioxidant capacity for human health. However, to date, only a few genetic data are available, which limits exploring its genetic diversity and developing new genetic studies for its improvement. We report the poro-poro plastid genome to expand the knowledge of its molecular markers, evolutionary studies, molecular pathways, and conservation genetics. The complete chloroplast (cp) genome is 163,451 bp in length with a typical quadripartite structure, containing a large single-copy region of 85,525 bp and a small single-copy region of 13,518 bp, separated by a pair of inverted repeat regions (IR) of 32,204 bp, and the overall GC content was 36.87%. This cp genome contains 128 genes (110 genes were unique and 18 genes were found duplicated in each IR region), including 84 protein-coding genes, 36 transfer RNA-coding genes, eight ribosomal RNA-coding genes, and 13 genes with introns (11 genes with one intron and two genes with two introns). The inverted repeat region boundaries among species were similar in organization, gene order, and content, with a few revisions. The phylogenetic tree reconstructed based on single-copy orthologous genes and maximum likelihood analysis demonstrates poro-poro is most closely related to Passiflora menispermifolia and Passiflora oerstedii. In summary, our study constitutes a valuable resource for studying molecular evolution, phylogenetics, and domestication. It also provides a powerful foundation for conservation genetics research and plant breeding programs. To our knowledge, this is the first report on the plastid genome of Passiflora tripartita var. mollissima from Peru.

The complete chloroplast genome of Calophyllum soulattri Burm. f. (Calophyllaceae)

Calophyllum soulattri Burm. f. (1768) is an evergreen tree native to Southeast Asia, Australia, and the Solomon Islands. It is known for its medicinal uses and has been utilized in traditional folk medicine. However, genomic resources for this species are still unavailable. In this study, we sequenced and assembled the first complete chloroplast genome of C. soulattri using next-generation sequencing data. The chloroplast genome of C. soulattri is 161,381 bp in length with a total GC content of 36.36%. The chloroplast genome contains a large single copy (LSC) region of 88,680 bp, a small single copy (SSC) region of 17,453 bp, and two inverted repeat (IR) regions of 27,624 bp each. Furthermore, the chloroplast genome has 131 genes, which include 86 protein-coding genes, 37 tRNA genes, and 8 rRNA genes. Phylogenetic analysis indicated that C. soulattri is clustered in the same branch with C. inophyllum and is closely related to Mesua ferrea.

Fifteen complete chloroplast genomes of Trapa species (Trapaceae): insight into genome structure, comparative analysis and phylogenetic relationships

BACKGROUND

Trapa L. is a floating-leaved aquatic plant with important economic and ecological values. However, the species identification and phylogenetic relationship within Trapa are still controversial, which necessitates the need for plastid genome information of Trapa. In this study, complete chloroplast genomes of 13 Trapa species/taxa were sequenced and annotated. Combined with released sequences, comparative analyses of chloroplast genomes were performed on the 15 Trapa species/taxa for the first time.

RESULTS

The Trapa chloroplast genomes exhibited typical quadripartite structures with lengths from 155,453 to 155,559 bp. The gene orders and contents within Trapa were conservative, but several changes were found in the microstructure. The intron loss of rpl2, also detected in Lythraceae, was found in all Trapa species/taxa, suggesting close genetic relationship between Lythraceae and Trapaceae. Notably, two small-seed species (T. incisa and T. maximowiczii) showed the smallest genome size with 155,453 and 155,477 bp, respectively. Each cp genome contained the same 130 genes consisting of 85 protein-coding genes, 37 tRNA genes and 8 rRNA genes. Trapa species/taxa showed 37 (T. incisa and T. maximowiczii) to 41 (T. sibirica) long repeats, including forward, palindromic, reversed and complementary repeats. There were 110 (T. quadrispinosa) to 123 (T. incisa and T. maximowiczii) SSR (simple sequence repeat) loci in Trapa chloroplast genomes. Comparative analyses revealed that two hotspot regions (atpA-atpF and rps2-rpoC2) in Trapa chloroplast genomes could be served as potential molecular markers. Three phylogenetic analyses (ML, MP and BI) consistently showed that there were two clusters within Trapa, including large- and small-seed species/taxa, respectively; for the large-seed Trapa, they clustered according to their geographical origin and tubercle morphology on the surface of seeds.

CONCLUSION

In summary, we have acquired the sequences of 13 Trapa chloroplast genomes, and performed the comparative analyses within Trapa for the first time. The results have helped us better identify the Trapa species/taxa and deepen the understanding of genetic basis and phylogenetic relationship of Trapa, which will facilitate the effective management and utilization of the important genetic resources in the future.

A genome sequence resource for the genus Passiflora, the genome of the wild diploid species Passiflora organensis

The genus Passiflora comprises a large group of plants popularly known as passionfruit, much appreciated for their exotic flowers and edible fruits. The species (∼500) are morphologically variable (e.g., growth habit, size, and color of flowers) and are adapted to distinct tropical ecosystems. In this study, we generated the genome of the wild diploid species Passiflora organensis Gardner by adopting a hybrid assembly approach. Passiflora organensis has a small genome of 259 Mbp and a heterozygosity rate of 81%, consistent with its reproductive system. Most of the genome sequences could be integrated into its chromosomes with cytogenomic markers (satellite DNA) as references. The repeated sequences accounted for 58.55% of the total DNA analyzed, and the Tekay lineage was the prevalent retrotransposon. In total, 25,327 coding genes were predicted. Passiflora organensis retains 5,609 singletons and 15,671 gene families. We focused on the genes potentially involved in the locus determining self-incompatibility and the MADS-box gene family, allowing us to infer expansions and contractions within specific subfamilies. Finally, we recovered the organellar DNA. Structural rearrangements and two mitoviruses, besides relics of other mobile elements, were found in the chloroplast and mt-DNA molecules, respectively. This study presents the first draft genome assembly of a wild Passiflora species, providing a valuable sequence resource for genomic and evolutionary studies on the genus, and support for breeding cropped passionfruit species.

A Repertory of Rearrangements and the Loss of an Inverted Repeat Region in Passiflora Chloroplast Genomes

Chloroplast genomes (cpDNA) in angiosperms are usually highly conserved. Although rearrangements have been observed in some lineages, such as Passiflora, the mechanisms that lead to rearrangements are still poorly elucidated. In the present study, we obtained 20 new chloroplast genomes (18 species from the genus Passiflora, and Dilkea retusa and Mitostemma brevifilis from the family Passifloraceae) in order to investigate cpDNA evolutionary history in this group. Passiflora cpDNAs vary in size considerably, with ∼50 kb between shortest and longest. Large inverted repeat (IR) expansions were identified, and at the extreme opposite, the loss of an IR was detected for the first time in Passiflora, a rare event in angiosperms. The loss of an IR region was detected in Passiflora capsularis and Passiflora costaricensis, a species in which occasional biparental chloroplast inheritance has previously been reported. A repertory of rearrangements such as inversions and gene losses were detected, making Passiflora one of the few groups with complex chloroplast genome evolution. We also performed a phylogenomic study based on all the available cp genomes and our analysis implies that there is a need to reconsider the taxonomic classifications of some species in the group.

Rampant Nuclear Transfer and Substitutions of Plastid Genes in Passiflora

Gene losses in plastid genomes (plastomes) are often accompanied by functional transfer to the nucleus or substitution of an alternative nuclear-encoded gene. Despite the highly conserved gene content in plastomes of photosynthetic land plants, recent gene loss events have been documented in several disparate angiosperm clades. Among these lineages, Passiflora lacks several essential ribosomal genes, rps7, rps16, rpl20, rpl22, and rpl32, the two largest plastid genes, ycf1 and ycf2, and has a highly divergent rpoA. Comparative transcriptome analyses were performed to determine the fate of the missing genes in Passiflora. Putative functional transfers of rps7, rpl22, and rpl32 to nucleus were detected, with the nuclear transfer of rps7, representing a novel event in angiosperms. Plastid-encoded rps7 was transferred into the intron of a nuclear-encoded plastid-targeted thioredoxin m-type gene, acquiring its plastid transit peptide (TP). Plastid rpl20 likely experienced a novel substitution by a duplicated, nuclear-encoded mitochondrial-targeted rpl20 that has a similar gene structure. Additionally, among rosids, evidence for a third independent transfer of rpl22 in Passiflora was detected that gained a TP from a nuclear gene containing an organelle RNA recognition motif. Nuclear transcripts representing rpoA, ycf1, and ycf2 were not detected. Further analyses suggest that the divergent rpoA remains functional and that the gene is under positive or purifying selection in different clades. Comparative analyses indicate that alternative translocon and motor protein complexes may have substituted for the loss of ycf1 and ycf2 in Passiflora.

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.

The evolutionary fate of rpl32 and rps16 losses in the Euphorbia schimperi (Euphorbiaceae) plastome

Gene transfers from mitochondria and plastids to the nucleus are an important process in the evolution of the eukaryotic cell. Plastid (pt) gene losses have been documented in multiple angiosperm lineages and are often associated with functional transfers to the nucleus or substitutions by duplicated nuclear genes targeted to both the plastid and mitochondrion. The plastid genome sequence of Euphorbia schimperi was assembled and three major genomic changes were detected, the complete loss of rpl32 and pseudogenization of rps16 and infA. The nuclear transcriptome of E. schimperi was sequenced to investigate the transfer/substitution of the rpl32 and rps16 genes to the nucleus. Transfer of plastid-encoded rpl32 to the nucleus was identified previously in three families of Malpighiales, Rhizophoraceae, Salicaceae and Passifloraceae. An E. schimperi transcript of pt SOD-1-RPL32 confirmed that the transfer in Euphorbiaceae is similar to other Malpighiales indicating that it occurred early in the divergence of the order. Ribosomal protein S16 (rps16) is encoded in the plastome in most angiosperms but not in Salicaceae and Passifloraceae. Substitution of the E. schimperi pt rps16 was likely due to a duplication of nuclear-encoded mitochondrial-targeted rps16 resulting in copies dually targeted to the mitochondrion and plastid. Sequences of RPS16-1 and RPS16-2 in the three families of Malpighiales (Salicaceae, Passifloraceae and Euphorbiaceae) have high sequence identity suggesting that the substitution event dates to the early divergence within Malpighiales.

The effect of the root-colonizing Piriformospora indica on passion fruit (Passiflora edulis) development: Initial defense shifts to fitness benefits and higher fruit quality

Passion fruit (Passiflora edulis) has an important economic value as exotic ingredient in juice blends. We inoculated the passion fruit cultivar Passiflora edulis Sims f. edulis's roots with the beneficial root-colonizing fungus Piriformospora indica under greenhouse conditions. The experiments were performed at three different locations and times (between 2017 and 2019). After transient initial growth retardation associated with a mild salicylic-acid (SA)-dependent defense activation and reduced sucrose metabolism, plant performance and growth are promoted during later stages. The elevated SA level in the aerial parts stimulates the plant immune system and promotes pathogen resistance in the adult plants and the fruit peels. P. indica stimulates the fruit size and fruit quality, and the higher amounts of defense-related secondary metabolites in the peels restrict growth of herbivorous insect larvae fed with peel extracts. We conclude that application of P. indica to passion fruits stimulates the plants' immune system and improves the fruits' quality.

Chromosome-scale genome assembly provides insights into the evolution and flavor synthesis of passion fruit (Passiflora edulis Sims)

Passion fruit (Passiflora edulis Sims) is an economically valuable fruit that is cultivated in tropical and subtropical regions of the world. Here, we report an ~1341.7 Mb chromosome-scale genome assembly of passion fruit, with 98.91% (~1327.18 Mb) of the assembly assigned to nine pseudochromosomes. The genome includes 23,171 protein-coding genes, and most of the assembled sequences are repetitive sequences, with long-terminal repeats (LTRs) being the most abundant. Phylogenetic analysis revealed that passion fruit diverged after Brassicaceae and before Euphorbiaceae. Ks analysis showed that two whole-genome duplication events occurred in passion fruit at 65 MYA and 12 MYA, which may have contributed to its large genome size. An integrated analysis of genomic, transcriptomic, and metabolomic data showed that 'alpha-linolenic acid metabolism', 'metabolic pathways', and 'secondary metabolic pathways' were the main pathways involved in the synthesis of important volatile organic compounds (VOCs) in passion fruit, and this analysis identified some candidate genes, including GDP-fucose Transporter 1-like, Tetratricopeptide repeat protein 33, protein NETWORKED 4B isoform X1, and Golgin Subfamily A member 6-like protein 22. In addition, we identified 13 important gene families in fatty acid pathways and eight important gene families in terpene pathways. Gene family analysis showed that the ACX, ADH, ALDH, and HPL gene families, especially ACX13/14/15/20, ADH13/26/33, ALDH1/4/21, and HPL4/6, were the key genes for ester synthesis, while the TPS gene family, especially PeTPS2/3/4/24, was the key gene family for terpene synthesis. This work provides insights into genome evolution and flavor trait biology and offers valuable resources for the improved cultivation of passion fruit.

Plastid Genomes of Flowering Plants: Essential Principles

The plastid genome (plastome ) has proved a valuable source of data for evaluating evolutionary relationships among angiosperms. Through basic and applied approaches, plastid transformation technology offers the potential to understand and improve plant productivity, providing food, fiber, energy, and medicines to meet the needs of a burgeoning global population. The growing genomic resources available to both phylogenetic and biotechnological investigations is allowing novel insights and expanding the scope of plastome research to encompass new species. In this chapter, we present an overview of some of the seminal and contemporary research that has contributed to our current understanding of plastome evolution and attempt to highlight the relationship between evolutionary mechanisms and the tools of plastid genetic engineering.

The Complete Chloroplast Genome of Plukenetia volubilis Provides Insights Into the Organelle Inheritance

Plukenetia volubilis L. (Malpighiales: Euphorbiaceae), also known as Sacha inchi, is considered a promising crop due to its high seed content of unsaturated fatty acids (UFAs), all of them highly valuable for food and cosmetic industries, but the genetic basis of oil biosynthesis of this non-model plant is still insufficient. Here, we sequenced the total DNA of Sacha inchi by using Illumina and Nanopore technologies and approached a de novo reconstruction of the whole nucleotide sequence and the organization of its 164,111 bp length of the chloroplast genome, displaying two copies of an inverted repeat sequence [inverted repeat A (IRA) and inverted repeat B (IRB)] of 28,209 bp, each one separating a small single copy (SSC) region of 17,860 bp and a large single copy (LSC) region of 89,833 bp. We detected two large inversions on the chloroplast genome that were not presented in the previously reported sequence and studied a promising cpDNA marker, useful in phylogenetic approaches. This chloroplast DNA (cpDNA) marker was used on a set of five distinct Colombian cultivars of P. volubilis from different geographical locations to reveal their phylogenetic relationships. Thus, we evaluated if it has enough resolution to genotype cultivars, intending to crossbreed parents and following marker's trace down to the F1 generation. We finally elucidated, by using molecular and cytological methods on cut flower buds, that the inheritance mode of P. volubilis cpDNA is maternally transmitted and proposed that it occurs as long as it is physically excluded during pollen development. This de novo chloroplast genome will provide a valuable resource for studying this promising crop, allowing the determination of the organellar inheritance mechanism of some critical phenotypic traits and enabling the use of genetic engineering in breeding programs to develop new varieties.

Chloroplast Genomes of Two Species of Cypripedium: Expanded Genome Size and Proliferation of AT-Biased Repeat Sequences

The size of the chloroplast genome (plastome) of autotrophic angiosperms is generally conserved. However, the chloroplast genomes of some lineages are greatly expanded, which may render assembling these genomes from short read sequencing data more challenging. Here, we present the sequencing, assembly, and annotation of the chloroplast genomes of Cypripedium tibeticum and Cypripedium subtropicum. We de novo assembled the chloroplast genomes of the two species with a combination of short-read Illumina data and long-read PacBio data. The plastomes of the two species are characterized by expanded genome size, proliferated AT-rich repeat sequences, low GC content and gene density, as well as low substitution rates of the coding genes. The plastomes of C. tibeticum (197,815 bp) and C. subtropicum (212,668 bp) are substantially larger than those of the three species sequenced in previous studies. The plastome of C. subtropicum is the longest one of Orchidaceae to date. Despite the increase in genome size, the gene order and gene number of the plastomes are conserved, with the exception of an ∼75 kb large inversion in the large single copy (LSC) region shared by the two species. The most striking is the record-setting low GC content in C. subtropicum (28.2%). Moreover, the plastome expansion of the two species is strongly correlated with the proliferation of AT-biased non-coding regions: the non-coding content of C. subtropicum is in excess of 57%. The genus provides a typical example of plastome expansion induced by the expansion of non-coding regions. Considering the pros and cons of different sequencing technologies, we recommend hybrid assembly based on long and short reads applied to the sequencing of plastomes with AT-biased base composition.

Selection of somaclonal variants of maracuyá (passiflora Edulis var Flavicarpa. Deneger) tolerants to water deficit

Climate change will have an impact on the Colombian agricultural sector, by 2050 increases in temperature and distribution of erratic rainfall are expected. Passion fruit cultivation does not tolerate water deficit, it reduces flower induction, generates fruit drop and defoliation. To tackle this problem, somaclonal variants (VS) of passion fruit were selected in-vitro, seeking tolerance to water deficit. Four phases were developed: I) callogenesis, II) direct and indirect organogenesis, II) Induction and evaluation of the water deficit with Polyethylene glycol 6000 (PEG 6000) and IV) in vitro selection of VS by morphometric measurements, chlorophyll and total sugars contents. Differences in callogenesis were found with different concentrations of 2,4-D, the concentration of 2 mg • L-1 presented better results producing calluses in less time and in greater quantity (8 days, 90% of the leaf area). In indirect and direct organogenesis the medium MS + ANA + BAP (0.3: 0.6), showed significant statistical differences with respect to other means, for the variables root length (15.14 cm), stem (16.72 cm) and leaves ( 14.51 cm) and root thickness (0.76 cm) stem (1.25) and leaf width (6.75). The influence of PEG 6000 showed significant differences, the treatment with 30 g • L-1 showed the smallest leaf width, the greatest width was found in 25 g • L-1. Statistical differences were found in chlorophyll levels and total sugar contents, the highest contents were recorded in the VS 25VS1, showing the possibility of obtaining seedlings tolerant to the water deficit of passion fruit by inducing somaclonal variation.

Chloroplast genome features of an important medicinal and edible plant: Houttuynia cordata (Saururaceae)

Houttuynia cordata (Saururaceae), an ancient and relic species, has been used as an important medicinal and edible plant in most parts of Asia. However, because of the lack of genome information and reliable molecular markers, studies on its population structure, or phylogenetic relationships with other related species are still rare. Here, we de novo assembled the complete chloroplast (cp) genome of H. cordata using the integration of the long PacBio and short Illumina reads. The cp genome of H. cordata showed a typical quadripartite cycle of 160,226 bp. This included a pair of inverted repeats (IRa and IRb) of 26,853 bp, separated by a large single-copy (LSC) region of 88,180 bp and a small single-copy (SSC) region of 18,340 bp. A total of 112 unique genes, including 79 protein-coding genes, 29 tRNA genes, and four rRNA genes, were identified in this cp genome. Eighty-one genes were located on the LSC region, 13 genes were located on the SSC region, and 17 two-copy genes were located on the IR region. Additionally, 48 repeat sequences and 86 SSR loci, which can be used as genomic markers for population structure analysis, were also detected. Phylogenetic analysis using 21 cp genomes of the Piperales family demonstrated that H. cordata had a close relationship with the species within the Aristolochia genus. Moreover, the results of mVISTA analysis and comparisons of IR regions demonstrated that the cp genome of H. cordata was conserved with that of the Aristolochia species. Our results provide valuable information for analyzing the genetic diversity and population structure of H. cordata, which can contribute to further its genetic improvement and breeding.

Complete chloroplast genome sequence of Caryocar brasiliense Camb. (Caryocaraceae) and comparative analysis brings new insights into the plastome evolution of Malpighiales

Caryocar brasiliense (Caryocaraceae) is a Neotropical tree species widely distributed in Brazilian Savannas. This species is very popular in central Brazil mainly by the use of its fruits in the local cuisine, and indeed it is one of the candidates, among Brazilian native plants, for fast track incorporation into cropping systems. Here we sequenced the complete chloroplast genome of C. brasiliense and used the data to access its genomic resources using high-throughput sequencing. The chloroplast exhibits a genome length of 165,793 bp and the typical angiosperm quadripartite structure with two copies of an inverted repeat sequence (IRa and IRb) of 34,902 bp each, separating a small single copy (SSC) region of 11,852 bp and a large single copy (LSC) region of 84,137 bp. The annotation analysis identified 136 genes being 87 protein-coding, eight rRNA and 37 tRNA genes. We identified 49 repetitive DNA elements and 85 microsatellites. A bayesian phylogenetic analysis helped to understand previously unresolved relationships in Malpighiales, placing Caryocaraceae as a separated group in the order, with high supported nodes. This study synthetizes valuable information for further studies allowing a better understanding of evolutionary patterns in the group and providing resources for future breeding programs.

Comparative Plastome Analysis of Root- and Stem-Feeding Parasites of Santalales Untangle the Footprints of Feeding Mode and Lifestyle Transitions

In plants, parasitism triggers the reductive evolution of plastid genomes (plastomes). To disentangle the molecular evolutionary associations between feeding on other plants below- or aboveground and general transitions from facultative to obligate parasitism, we analyzed 34 complete plastomes of autotrophic, root- and stem-feeding hemiparasitic, and holoparasitic Santalales. We observed inexplicable losses of housekeeping genes and tRNAs in hemiparasites and dramatic genomic reconfiguration in holoparasitic Balanophoraceae, whose plastomes have exceptionally low GC contents. Genomic changes are related primarily to the evolution of hemi- or holoparasitism, whereas the transition from a root- to a stem-feeding mode plays no major role. In contrast, the rate of molecular evolution accelerates in a stepwise manner from autotrophs to root- and then stem-feeding parasites. Already the ancestral transition to root-parasitism coincides with a relaxation of selection in plastomes. Another significant selectional shift in plastid genes occurs as stem-feeders evolve, suggesting that this derived form coincides with trophic specialization despite the retention of photosynthetic capacity. Parasitic Santalales fill a gap in our understanding of parasitism-associated plastome degeneration. We reveal that lifestyle-genome associations unfold interdependently over trophic specialization and feeding mode transitions, where holoparasitic Balanophoraceae provide a system for exploring the functional realms of plastomes.

Insights Into Chloroplast Genome Evolution Across Opuntioideae (Cactaceae) Reveals Robust Yet Sometimes Conflicting Phylogenetic Topologies

Chloroplast genomes (plastomes) are frequently treated as highly conserved among land plants. However, many lineages of vascular plants have experienced extensive structural rearrangements, including inversions and modifications to the size and content of genes. Cacti are one of these lineages, containing the smallest plastome known for an obligately photosynthetic angiosperm, including the loss of one copy of the inverted repeat (∼25 kb) and the ndh gene suite, but only a few cacti from the subfamily Cactoideae have been sufficiently characterized. Here, we investigated the variation of plastome sequences across the second-major lineage of the Cactaceae, the subfamily Opuntioideae, to address (1) how variable is the content and arrangement of chloroplast genome sequences across the subfamily, and (2) how phylogenetically informative are the plastome sequences for resolving major relationships among the clades of Opuntioideae. Our de novo assembly of the Opuntia quimilo plastome recovered an organelle of 150,347 bp in length with both copies of the inverted repeat and the presence of all the ndh gene suite. An expansion of the large single copy unit and a reduction of the small single copy unit was observed, including translocations and inversion of genes, as well as the putative pseudogenization of some loci. Comparative analyses among all clades within Opuntioideae suggested that plastome structure and content vary across taxa of this subfamily, with putative independent losses of the ndh gene suite and pseudogenization of genes across disparate lineages, further demonstrating the dynamic nature of plastomes in Cactaceae. Our plastome dataset was robust in resolving three tribes with high support within Opuntioideae: Cylindropuntieae, Tephrocacteae and Opuntieae. However, conflicting topologies were recovered among major clades when exploring different assemblies of markers. A plastome-wide survey for highly informative phylogenetic markers revealed previously unused regions for future use in Sanger-based studies, presenting a valuable dataset with primers designed for continued evolutionary studies across Cactaceae. These results bring new insights into the evolution of plastomes in cacti, suggesting that further analyses should be carried out to address how ecological drivers, physiological constraints and morphological traits of cacti may be related with the common rearrangements in plastomes that have been reported across the family.

Long-reads reveal that Rhododendron delavayi plastid genome contains extensive repeat sequences, and recombination exists among plastid genomes of photosynthetic Ericaceae

BACKGROUND

Rhododendron delavayi Franch. var. delavayi is a wild ornamental plant species in Guizhou Province, China. The lack of its plastid genome information seriously hinders the further application and conservation of the valuable resource.

METHODS

The complete plastid genome of R. delavayi was assembled from long sequence reads. The genome was then characterized, and compared with those of other photosynthetic Ericaceae species.

RESULTS

The plastid genome of R. delavayi has a typical quadripartite structure, and a length of 202,169 bp. It contains a large number of repeat sequences and shows preference for codon usage. The comparative analysis revealed the irregular recombination of gene sets, including rearrangement and inversion, in the large single copy region. The extreme expansion of the inverted repeat region shortened the small single copy, and expanded the full length of the genome. In addition, consistent with traditional taxonomy, R. delavayi with nine other species of the same family were clustered into Ericaceae based on the homologous protein-coding sequences of the plastid genomes. Thus, the long-read assembly of the plastid genome of R. delavayi would provide basic information for the further study of the evolution, genetic diversity, and conservation of R. delavayi and its relatives.

Implications of plastome evolution in the true lilies (monocot order Liliales)

The families of the monocot order Liliales exhibit highly contrasting characteristic of photosynthetic and mycoheterotrophic life histories. Although previous phylogenetic and morphological studies of Liliales have been conducted, they have not examined molecular evolution associated with this contrasting phenomenon. Here, we conduct the first comparative plastome study of all ten families of Liliales using 29 newly sequenced plastid genomes analyzed together with previously published data. We also present a phylogenetic analysis for Liliales of 78 plastid genes combined with 22 genes from all three genomes (nuclear 18S rDNA and phyC; 17 plastid genes; and mitochondrial matR, atpA, and cob). Within the newly generated phylogenetic tree of Liliales, we evaluate the ancestral state changes of selected morphological traits in the order. There are no significant differences in plastid genome features among species that show divergent characteristics correlated with family circumscriptions. However, the results clearly differentiate between photosynthetic and mycoheterotrophic taxa of Liliales in terms of genome structure, and gene content and order. The newly sequenced plastid genomes and combined three-genome data revealed Smilacaceae as sister to Liliaceae instead of Philesiaceae and Ripogonaceae. Additionally, we propose a revised familial classification system of Liliales that consists of nine families, considering Ripogonaceae a synonym of Philesiaceae. The ancestral state reconstruction indicated synapomorphies for each family of Liliales, except Liliaceae, Melanthiaceae and Colchicaceae. A taxonomic key for all nine families of Liliales is also provided.

Comparative analyses of chloroplast genomes from 13 Lagerstroemia (Lythraceae) species: identification of highly divergent regions and inference of phylogenetic relationships

Seven divergence hotspots as plastid markers for DNA barcoding was selected, and the phylogeny of 13 Lagerstroemia species based on the cp genome data was reconstructed within Myrtales. The Lagerstroemia species used in this study originated in China and have high economic and ecological value. The shared interspecific morphological characteristics and intraspecific morphological variation resulting from hybridization among Lagerstroemia taxa have made resolving their classification problems and phylogenetic relationships difficult. Systematic comparative genomic analysis has been shown to resolve phylogenetic relationships. We sequenced and annotated 6 Lagerstroemia cp genomes (Lagerstroemia excelsa, Lagerstroemia limii, Lagerstroemia siamica, Lagerstroemia tomentosa, Lagerstroemia venusta, and Lagerstroemia calyculata) for the first time and combined them with previously published genomes for Lagerstroemia species. Bioinformatics was used to analyse the 13 cp genomes in terms of gene structure and organization, codon usage, contraction and expansion of inverted repeat regions, repeat structure, divergence hotspots, species pairwise Ka/Ks ratios and phylogenetic relationships. The length varied between 152,049 bp in Lagerstroemia subcostata and 152,521 bp in L. venusta. We selected seven divergence hotspots in the cp genomes that had the potential to act as plastid markers to distinguish Lagerstroemia species. The phylogenetic relationships within Myrtales inferred from the cp genomes of 13 Lagerstroemia species and 27 other Myrtales species were highly supported, which illustrated several novel relationships within Myrtales. Taken together, our results provide comprehensive chloroplast genomic resources, which can be used further for species identification and molecular breeding of Lagerstroemia species.

Initial Characterization of the Chloroplast Genome of Vicia sepium, an Important Wild Resource Plant, and Related Inferences About Its Evolution

Lack of complete genomic information concerning Vicia sepium (Fabaceae: Fabeae) precludes investigations of evolution and populational diversity of this perennial high-protein forage plant suitable for cultivation in extreme conditions. Here, we present the complete and annotated chloroplast genome of this important wild resource plant. V. sepium chloroplast genome includes 76 protein-coding genes, 29 tRNA genes, 4 rRNA genes, and 1 pseudogene. Its 124,095 bp sequence has a loss of one inverted repeat (IR). The GC content of the whole genome, the protein-coding, intron, tRNA, rRNA, and intergenic spacer regions was 35.0%, 36.7%, 34.6%, 52.3%, 54.2%, and 29.2%, respectively. Comparative analyses with plastids from related genera belonging to Fabeae demonstrated that the greatest variation in the V. sepium genome length occurred in protein-coding regions. In these regions, some genes and introns were lost or gained; for example, ycf4, clpP intron, and rpl16 intron deletions and rpl20 and ORF292 insertions were observed. Twelve highly divergent regions, 66 simple sequence repeats (SSRs) and 27 repeat sequences were also found in these regions. Detailed evolutionary rate analysis of protein-coding genes showed that Vicia species exhibit additional interesting characteristics including positive selection of ccsA, clpP, rpl32, rpl33, rpoC1, rps15, rps2, rps4, and rps7, and the evolutionary rates of atpA, accD, and rps2 in Vicia are significantly accelerated. These genes are important candidate genes for understanding the evolutionary strategies of Vicia and other genera in Fabeae. The phylogenetic analysis showed that Vicia and Lens are included in the same clade and that Vicia is paraphyletic. These results provide evidence regarding the evolutionary history of the chloroplast genome.

-Complete plastid genome sequences of two species of the Neotropical genus Brunellia (Brunelliaceae)

Here we present the first two complete plastid genomes for Brunelliaceae, a Neotropical family with a single genus, Brunellia. We surveyed the entire plastid genome in order to find variable cpDNA regions for further phylogenetic analyses across the family. We sampled morphologically different species, B. antioquensis and B. trianae, and found that the plastid genomes are 157,685 and 157,775 bp in length and display the typical quadripartite structure found in angiosperms. Despite the clear morphological distinction between both species, the molecular data show a very low level of divergence. The amount of nucleotide substitutions per site is one of the lowest reported to date among published congeneric studies (π = 0.00025). The plastid genomes have gene order and content coincident with other COM (Celastrales, Oxalidales, Malpighiales) relatives. Phylogenetic analyses of selected superrosid representatives show high bootstrap support for the ((C,M)O) topology. The N-fixing clade appears as the sister group of the COM clade and Zygophyllales as the sister to the rest of the fabids group.

Development of molecular markers for invasive alien plants in Korea: a case study of a toxic weed, Cenchrus longispinus L., based on next generation sequencing data

BACKGROUND

Genomic data play an important role in plant research because of its implications in studying genomic evolution, phylogeny, and developing molecular markers. Although the information of invasive alien plants was collected, the genomic data of those species have not been intensively studied.

METHODS

We employ the next generation sequencing and PCR methods to explore the genomic data as well as to develop and test the molecular markers.

RESULTS

In this study, we characterize the chloroplast genomes (cpDNA) of Cenchrus longispinus and C. echinatus, of which the lengths are 137,144 and 137,131 bp, respectively. These two newly sequenced genomes include 78 protein-coding genes, 30 tRNA, and four rRNA. There are 56 simple single repeats and 17 forward repeats in the chloroplast genome of C. longispinus. Most of the repeats locate in non-coding regions. However, repeats can be found in infA, ndhD, ndhH, ndhK, psbC, rpl22, rpoC2, rps14, trnA-UGC, trnC-GCA, trnF-GAA, trnQ-UUG, trnS-UGA, trnS-GCU, and ycf15. The phylogenomic analysis revealed the monophyly of Cenchrus but not Panicum species in tribe Paniceae. The single nucleotide polymorphism sites in atpB, matK, and ndhD were successfully used for developing molecular markers to distinguish C. longispinus and related taxa. The simple PCR protocol for using the newly developed molecular markers was also provided.

Characterization of 20 complete plastomes from the tribe Laureae (Lauraceae) and distribution of small inversions

Lindera Thunb. (Lauraceae) consists of approximately 100 species, mainly distributed in the temperate and tropical regions of East Asia. In this study, we report 20 new, complete plastome sequences including 17 Lindera species and three related species, Actinodaphne lancifolia, Litsea japonica and Sassafras tzumu. The complete plastomes of Lindera range from 152,502 bp (L. neesiana) to 154,314 bp (L. erythrocarpa) in length. Eleven small inversion (SI) sites are documented among the plastomes. Six of the 11 SI sites are newly reported and they locate in rpoB-trnC, psbC-trnS, petA-psbJ, rpoA and ycf2 regions. The distribution patterns of SIs are useful for species identification. An average of 83 simple sequence repeats (SSRs) were detected in each plastome. The mono-SSRs accounted for 72.7% of total SSRs, followed by di- (12.4%), tetra- (9.4%), tri- (4.2%), and penta-SSRs (1.3%). Of these SSRs, 64.6% were distributed in an intergenic spacer (IGS) region. In addition, 79.8% of the SSRs are located in a large single copy (LSC) region. In contrast, almost no SSRs are distributed in inverted repeat (IR) regions. The SSR loci are useful to identifying species but the phylogenetic value is low because the majority of them show autapomorphic status or highly homoplastic characteristics. The nucleotide diversity (Pi) values also indicated the conserved nature of the IR region compared to LSC and small single copy (SSC) regions. Five spacer regions with high Pi values, trnH-psbA, petA-psbJ and ndhF-rpl32, rpl32-trnL and Ψycf1-ndhF, have a potential use for the molecular identification study of Lindera and related species. Lindera species form a paraphyletic group in the plastome tree because of the inclusion of related genera such as Actinodaphne, Laurus, Litsea and Neolitsea. A former member of tribe Laureae, Sassafras, forms a clade with the tribe Cinnamomeae. The SIs do not affect the phylogenetic relationship of Laureae. This result indicated that ancient plastome captures may have contribute to the mixed intergeneric relationship of Laureae. Alternatively, the result may indicate that the morphological characters defined the genera of Lauraceae originated for several times.

Developing Chloroplast Genomic Resources from 25 Avena Species for the Characterization of Oat Wild Relative Germplasm

Chloroplast (cp) genomics will play an important role in the characterization of crop wild relative germplasm conserved in worldwide gene banks, thanks to the advances in genome sequencing. We applied a multiplexed shotgun sequencing procedure to sequence the cp genomes of 25 Avena species with variable ploidy levels. Bioinformatics analysis of the acquired sequences generated 25 de novo genome assemblies ranging from 135,557 to 136,006 bp. The gene annotations revealed 130 genes and their duplications, along with four to six pseudogenes, for each genome. Little differences in genome structure and gene arrangement were observed across the 25 species. Polymorphism analyses identified 1313 polymorphic sites and revealed an average of 277 microsatellites per genome. Greater nucleotide diversity was observed in the short single-copy region. Genome-wide scanning of selection signals suggested that six cp genes were under positive selection on some amino acids. These research outputs allow for a better understanding of oat cp genomes and evolution, and they form an essential set of cp genomic resources for the studies of oat evolutionary biology and for oat wild relative germplasm characterization.

Characterization of the complete chloroplast genome of a purple passion flower variety ‘Pingtang No.1’ (Passiflora edulia Sims) in China and phylogenetic relationships

Passion flower (Passiflora edulia Sims) is an important fruit that is of great economic importance. In this study, we presented the chloroplast genome of a purple passion flower variety ‘Pingtang No.1’ in China using BGISEQ-500 sequencing. Its chloroplast genome is 152,621 bp in size. It contains a pair of inverted repeat regions of 25,989 bp, each separating a small single copy region of 13,352 bp and a large single copy region of 85,141 bp. Totally, 111 unique genes, including 77 protein coding genes, 30 tRNAs, and 4 rRNAs, were identified and annotated in the chloroplast genome. Phylogenetic maximum likelihood analysis based on chloroplast genomes of 35 plant species, mainly from the genus Passiflora indicated that ‘Pingtang No.1’ and yellow passion flower ‘IAPAR-123’ (Passiflora edulis) cluster together. The chloroplast genome can be used for a better understanding of the evolutionary relationships of plant species of the family Passifloraceae, especially the genus Passiflora.

Determination of the evolutionary pressure on Camellia oleifera on Hainan Island using the complete chloroplast genome sequence

Camellia oleifera is one of the four largest woody edible oil plants in the world with high ecological and medicinal values. Due to frequent interspecific hybridization, it was difficult to study its genetics and evolutionary history. This study used C. oleifera that was collected on Hainan Island to conduct our research. The unique island environment makes the quality of tea oil higher than that of other species grown in the mainland. Moreover, a long-term geographic isolation might affect gene structure. In order to better understand the molecular biology of this species, protect excellent germplasm resources, and promote the population genetics and phylogenetic studies of Camellia plants, high-throughput sequencing technology was used to obtain the chloroplast genome sequence of Hainan C. oleifera. The results showed that the whole chloroplast genome of C. oleifera in Hainan was 156,995 bp in length, with a typical quadripartite structure of a large single copy (LSC) region of 86,648 bp, a small single copy (SSC) region of 18,297 bp, and a pair of inverted repeats (IRs) of 26,025 bp. The whole genome encoded a total of 141 genes (115 different genes), including 88 protein-coding genes, 45 tRNA genes, and eight rRNA genes. Among these genes, nine genes contained one intron, two genes contained two introns, and four overlapping genes were also detected. The total GC content of Hainan C. oleifera's chloroplast genome was 37.29%. The chloroplast genome structure characteristics of Hainan C. oleifera were compared with mainland C. oleifera and those of the other eight closely related Theaceae species; it was found that the contractions and expansions of the IR/LSC and IR/SSC regions affected the length of chloroplast genome. The chloroplast genome sequences of these Theaceae species were highly similar. A comparative analysis indicated that the Theaceae species were conserved in structure and evolution. A total of 51 simple sequence repeat (SSR) loci were detected in the chloroplast genome of Hainan C. oleifera, and all Camellia plants did not have pentanucleotide repeats, which could be used as a good marker in phylogenetic studies. We also detected seven long repeats, the base composition of all repeats was biased toward A/T, which was consistent with the codon bias. It was found that Hainan C. oleifera had a similar evolutionary relationship with C. crapnelliana, through the use of codons and phylogenetic analysis. This study can provide an effective genomic resource for the evolutionary history of Theaceae family.

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.

Highly accelerated rates of genomic rearrangements and nucleotide substitutions in plastid genomes of Passiflora subgenus Decaloba

Plastid genomes (plastomes) of photosynthetic angiosperms are for the most part highly conserved in their organization, mode of inheritance and rates of nucleotide substitution. A small number of distantly related lineages share a syndrome of features that deviate from this general pattern, including extensive genomic rearrangements, accelerated rates of nucleotide substitution, biparental inheritance and plastome-genome incompatibility. Previous studies of plastomes in Passiflora with limited taxon sampling suggested that the genus exhibits this syndrome. To examine this phenomenon further, 15 new plastomes from Passiflora were sequenced and combined with previously published data to examine the phylogenetic relationships, genome organization and evolutionary rates across all five subgenera and the sister genus Adenia. Phylogenomic analyses using 68 protein-coding genes shared by Passiflora generated a fully resolved and strongly supported tree that is congruent with previous phylogenies based on a few plastid and nuclear loci. This phylogeny was used to examine the distribution of plastome rearrangements across Passiflora. Multiple gene and intron losses and inversions were identified in Passiflora with some occurring in parallel and others that extended across the Passifloraceae. Furthermore, extensive expansions and contractions of the inverted repeat (IR) were uncovered and in some cases this resulted in exclusion of all ribosomal RNA genes from the IR. The most highly rearranged lineage was subgenus Decaloba, which experienced extensive IR expansion that incorporated up to 25 protein-coding genes usually located in large single copy region. Nucleotide substitution rate analyses of 68 protein-coding genes across the genus showed lineage- and locus-specific acceleration. Significant increase in dS, dN and dN/dS was detected for clpP across the genus and for ycf4 in certain lineages. Significant increases in dN and dN/dS for ribosomal subunits and plastid-encoded RNA polymerase genes were detected in the branch leading to the expanded IR-clade in subgenus Decaloba. This subgenus displays the syndrome of unusual features, making it an ideal system to investigate the dynamic evolution of angiosperm plastomes.

Plastid Genomes of Five Species of Riverweeds (Podostemaceae): Structural Organization and Comparative Analysis in Malpighiales

With the advent of next-generation sequencing technologies, whole-plastome data can be obtained as a byproduct of low-coverage sequencing of the plant genomic DNA. This provides an opportunity to study plastid evolution across groups, as well as testing phylogenetic relationships among taxa. Within the order Malpighiales (∼16,000 spp.), the Podostemaceae (∼300 spp.) stand out for their unique habit, living attached to rocks in fast-flowing aquatic habitats, and displaying highly modified morphologies that confound our understanding of their classification, biology, and evolution. In this study, we used genome skimming data to assemble the full plastid genome of 5 species within Podostemaceae. We analyzed our data in a comparative framework within Malpighiales to determine the structure, gene content, and rearrangements in the plastomes of the family. The Podostemaceae have one of the smallest plastid genomes reported so far for the Malpighiales, possibly due to variation in length of inverted repeat (IR) regions, gene loss, and intergenic region variation. We also detected a major inversion in the large single-copy region unique to the family. The uncommon loss or pseudogenization of ycf1 and ycf2 in angiosperms and in land plants in general is also found to be characteristic of Podostemaceae, but the compensatory mechanisms and implications of this and of the pseudogenization of accD, rpl22, and clpP and loss of rps16 remain to be explained in this group. In addition, we estimated a phylogenetic tree among selected species in Malpighiales. Our findings indicate that the Podostemaceae are a distinct lineage with long branches that suggest faster rates of evolution in the plastome of the group, compared with other taxa in the order. This study lays the foundations for future phylogenomic studies in the family.

The complete chloroplast genome sequences of three Spondias species reveal close relationship among the species

This study reports the complete chloroplast sequences of three Spondias species. The genome sequences were obtained for Spondias tuberosa, Spondias bahienses, and Spondias mombin using the Illumina sequencing technology by a combination of de novo methods and a reference-guided assembly using Sapindus mukorossi as reference. The genomes of S. tuberosa, S. bahiensis, and S. mombin had 162,036, 162,218, and 162,302 bp, respectively. The coding regions exhibited 130 genes, including 34-35 tRNAs and 4 rRNAs. The results revealed synteny among the genomes, with high conservation in the gene order and content and CG content. The inverted repeat regions (IRA and IRB) and the large and small single copies were very similar among the three genomes. The phylogenomic analysis reported similar topologies as that of previous studies, which used partial chloroplast, wherein S. mombin was the first diverging lineage, while S. tuberosa and S. bahiensis were derived, indicating that the phylogenetic analysis using partial or complete genome produces similar results. In summary, (1) we presented the first complete chloroplast genome for the genus Spondias, (2) phylogenies analyzed using the complete chloroplast genomes revealed a robust phylogenetic topology for Spondias, and (3) gene order, content, and orientation in Spondias are highly conserved.

Comparative Chloroplast Genomics at Low Taxonomic Levels: A Case Study Using Amphilophium (Bignonieae, Bignoniaceae)

Chloroplast (cp) genome organization, gene order, and content have long been considered conserved among land plants. Despite that, the generation of thousands of complete plastomes through next-generation sequencing (NGS) has challenged their conserved nature. In this study, we analyze 11 new complete plastomes of Amphilophium (Bignonieae, Bignoniaceae), a diverse genus of Neotropical lianas, and that of Anemopaegma prostratum. We explored the structure and content of the assembled plastomes and performed comparative analyses within Amphilophium and among other plastomes available for Bignoniaceae. The overall gene content and orientation of plastomes is similar in all species studied. Plastomes are not conserved among Amphilophium, showing significant differences in length (155,262-164,786 bp), number of genes duplicated in the IRs (eight, 18, or 19), and location of the SC/IR boundaries (i.e., LSC/IRa junction between rps19 and rpl2 genes, within petD, or within petB). Length differences reflect expansions of the IRs and contractions of the LSC regions. The plastome of A. prostratum is 168,172 bp, includes 19 duplicated genes, and has the LSC/IRa boundary located within the petB gene. Amphilophium plastomes show high nucleotide diversity, with many hypervariable regions, and 16 genes with signatures of positive selection. Multiple SSRs and repeat regions were identified for Amphilophium and Anemopaegma prostratum. The differences in structure detected within Amphilophium plastomes in terms of LSC/IR and IR/SSC boundaries, number of duplicated genes, and genome sizes are mostly shared between taxa that belong to the same clade. Our results bring new insights into the evolution of plastomes at low taxonomic levels.

A gene-rich fraction analysis of the Passiflora edulis genome reveals highly conserved microsyntenic regions with two related Malpighiales species

Passiflora edulis is the most widely cultivated species of passionflowers, cropped mainly for industrialized juice production and fresh fruit consumption. Despite its commercial importance, little is known about the genome structure of P. edulis. To fill in this gap in our knowledge, a genomic library was built, and now completely sequenced over 100 large-inserts. Sequencing data were assembled from long sequence reads, and structural sequence annotation resulted in the prediction of about 1,900 genes, providing data for subsequent functional analysis. The richness of repetitive elements was also evaluated. Microsyntenic regions of P. edulis common to Populus trichocarpa and Manihot esculenta, two related Malpighiales species with available fully sequenced genomes were examined. Overall, gene order was well conserved, with some disruptions of collinearity identified as rearrangements, such as inversion and translocation events. The microsynteny level observed between the P. edulis sequences and the compared genomes is surprising, given the long divergence time that separates them from the common ancestor. P. edulis gene-rich segments are more compact than those of the other two species, even though its genome is much larger. This study provides a first accurate gene set for P. edulis, opening the way for new studies on the evolutionary issues in Malpighiales genomes.

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.

The Linum usitatissimum L. plastome reveals atypical structural evolution, new editing sites, and the phylogenetic position of Linaceae within Malpighiales

The plastome of Linum usitatissimum was completely sequenced allowing analyses of evolution of genome structure, RNA editing sites, molecular markers, and indicating the position of Linaceae within Malpighiales. Flax (Linum usitatissimum L.) is an economically important crop used as food, feed, and industrial feedstock. It belongs to the Linaceae family, which is noted by high morphological and ecological diversity. Here, we reported the complete sequence of flax plastome, the first species within Linaceae family to have the plastome sequenced, assembled and characterized in detail. The plastome of flax is a circular DNA molecule of 156,721 bp with a typical quadripartite structure including two IRs of 31,990 bp separating the LSC of 81,767 bp and the SSC of 10,974 bp. It shows two expansion events from IRB to LSC and from IRB to SSC, and a contraction event in the IRA-LSC junction, which changed significantly the size and the gene content of LSC, SSC and IRs. We identified 109 unique genes and 2 pseudogenes (rpl23 and ndhF). The plastome lost the conserved introns of clpP gene and the complete sequence of rps16 gene. The clpP, ycf1, and ycf2 genes show high nucleotide and aminoacid divergence, but they still possibly retain the functionality. Moreover, we also identified 176 SSRs, 20 tandem repeats, and 39 dispersed repeats. We predicted in 18 genes a total of 53 RNA editing sites of which 32 were not found before in other species. The phylogenetic inference based on 63 plastid protein-coding genes of 38 taxa supports three major clades within Malpighiales order. One of these clades has flax (Linaceae) sister to Chrysobalanaceae family, differing from earlier studies that included Linaceae into the euphorbioid clade.

Comparative genomic analysis of Genlisea (corkscrew plants-Lentibulariaceae) chloroplast genomes reveals an increasing loss of the ndh genes

In the carnivorous plant family Lentibulariaceae, all three genome compartments (nuclear, chloroplast, and mitochondria) have some of the highest rates of nucleotide substitutions across angiosperms. While the genera Genlisea and Utricularia have the smallest known flowering plant nuclear genomes, the chloroplast genomes (cpDNA) are mostly structurally conserved except for deletion and/or pseudogenization of the NAD(P)H-dehydrogenase complex (ndh) genes known to be involved in stress conditions of low light or CO2 concentrations. In order to determine how the cpDNA are changing, and to better understand the evolutionary history within the Genlisea genus, we sequenced, assembled and analyzed complete cpDNA from six species (G. aurea, G. filiformis, G. pygmaea, G. repens, G. tuberosa and G. violacea) together with the publicly available G. margaretae cpDNA. In general, the cpDNA structure among the analyzed Genlisea species is highly similar. However, we found that the plastidial ndh genes underwent a progressive process of degradation similar to the other terrestrial Lentibulariaceae cpDNA analyzed to date, but in contrast to the aquatic species. Contrary to current thinking that the terrestrial environment is a more stressful environment and thus requiring the ndh genes, we provide evidence that in the Lentibulariaceae the terrestrial forms have progressive loss while the aquatic forms have the eleven plastidial ndh genes intact. Therefore, the Lentibulariaceae system provides an important opportunity to understand the evolutionary forces that govern the transition to an aquatic environment and may provide insight into how plants manage water stress at a genome scale.

Complete Chloroplast Genome of Pinus massoniana (Pinaceae): Gene Rearrangements, Loss of ndh Genes, and Short Inverted Repeats Contraction, Expansion

The chloroplast genome (CPG) of Pinus massoniana belonging to the genus Pinus (Pinaceae), which is a primary source of turpentine, was sequenced and analyzed in terms of gene rearrangements, ndh genes loss, and the contraction and expansion of short inverted repeats (IRs). P. massoniana CPG has a typical quadripartite structure that includes large single copy (LSC) (65,563 bp), small single copy (SSC) (53,230 bp) and two IRs (IRa and IRb, 485 bp). The 108 unique genes were identified, including 73 protein-coding genes, 31 tRNAs, and 4 rRNAs. Most of the 81 simple sequence repeats (SSRs) identified in CPG were mononucleotides motifs of A/T types and located in non-coding regions. Comparisons with related species revealed an inversion (21,556 bp) in the LSC region; P. massoniana CPG lacks all 11 intact ndh genes (four ndh genes lost completely; the five remained truncated as pseudogenes; and the other two ndh genes remain as pseudogenes because of short insertions or deletions). A pair of short IRs was found instead of large IRs, and size variations among pine species were observed, which resulted from short insertions or deletions and non-synchronized variations between "IRa" and "IRb". The results of phylogenetic analyses based on whole CPG sequences of 16 conifers indicated that the whole CPG sequences could be used as a powerful tool in phylogenetic analyses.