Paternal leakage of plastids rescues inter-lineage hybrids in Silene nutans

BACKGROUND AND AIMS

Organelle genomes are usually maternally inherited in angiosperms. However, biparental inheritance has been observed, especially in hybrids resulting from crosses between divergent genetic lineages. When it concerns the plastid genome, this exceptional mode of inheritance might rescue inter-lineage hybrids suffering from plastid-nuclear incompatibilities. Genetically differentiated lineages of Silene nutans exhibit strong postzygotic isolation owing to plastid-nuclear incompatibilities, highlighted by inter-lineage hybrid chlorosis and mortality. Surviving hybrids can exhibit variegated leaves, which might indicate paternal leakage of the plastid genome. We tested whether the surviving hybrids inherited the paternal plastid genome and survived thanks to paternal leakage.

METHODS

We characterized the leaf phenotype (fully green, variegated or white) of 504 surviving inter-lineage hybrids obtained from a reciprocal cross experiment among populations of four genetic lineages (W1, W2, W3 and E1) of S. nutans from Western Europe and genotyped 560 leaf samples (both green and white leaves for variegated hybrids) using six lineage-specific plastid single nucleotide polymorphisms.

KEY RESULTS

A high proportion of the surviving hybrids (≤98 %) inherited the paternal plastid genome, indicating paternal leakage. The level of paternal leakage depended on cross type and cross direction. The E1 and W2 lineages as maternal lineages led to the highest hybrid mortality and to the highest paternal leakage from W1 and W3 lineages in the few surviving hybrids. This was consistent with E1 and W2 lineages, which contained the most divergent plastid genomes. When W3 was the mother, more hybrids survived, and no paternal leakage was detected.

CONCLUSIONS

By providing a plastid genome potentially more compatible with the hybrid nuclear background, paternal leakage has the potential to rescue inter-lineage hybrids from plastid-nuclear incompatibilities. This phenomenon might slow down the speciation process, provided hybrid survival and reproduction can occur in the wild.

Plastid genome of Chenopodium petiolare from Trujillo, Peru

OBJECTIVES

The Peruvian Andean region is an important center for plant domestication. However, to date, there have been few genetic studies on native grain, which limits our understanding of their genetic diversity and the development of new genetic studies for their breeding. Herein, we revealed the plastid genome of Chenopodium petiolare to expand our knowledge of its molecular markers, evolutionary studies, and conservation genetics.

DATA DESCRIPTION

Total genomic DNA was extracted from fresh leaves (voucher: USM < PER > :MHN333570). The DNA was sequenced using Illumina Novaseq 6000 (Macrogen Inc., Seoul, Republic of Korea) and reads 152,064 bp in length, with a large single-copy region of 83,520 bp and small single-copy region of 18,108 bp were obtained. These reads were separated by a pair of inverted repeat regions (IR) of 25,218 bp, and the overall guanine and cytosine (GC) was 37.24%. The plastid genome contains 130 genes (111 genes were unique and 19 genes were found duplicated in each IR region), including 86 protein-coding genes, 36 transfer RNA-coding genes, eight ribosomal RNA-coding genes, and 25 genes with introns (21 genes with one intron and four genes with two introns). The phylogenetic tree reconstructed based on single-copy orthologous genes and maximum likelihood analysis indicated that Chenopodium petiolare is most closely related to Chenopodium quinoa.

Plastid genome data provide new insights into the dynamic evolution of the tribe Ampelopsideae (Vitaceae)

BACKGROUND

Ampelopsideae J. Wen & Z.L. Nie is a small-sized tribe of Vitaceae Juss., including ca. 47 species from four genera showing a disjunct distribution worldwide across all the continents except Antarctica. There are numerous species from the tribe that are commonly used as medicinal plants with immune-modulating, antimicrobial, and anti-hypertensive properties. The tribe is usually recognized into three clades, i.e., Ampelopsis Michx., Nekemias Raf., and the Southern Hemisphere clade. However, the relationships of the three clades differ greatly between the nuclear and the plastid topologies. There has been limited exploration of the chloroplast phylogenetic relationships within Ampelopsideae, and studies on the chloroplast genome structure of this tribe are only available for a few individuals. In this study, we aimed to investigate the evolutionary characteristics of plastid genomes of the tribe, including their genome structure and evolutionary insights.

RESULTS

We sequenced, assembled, and annotated plastid genomes of 36 species from the tribe and related taxa in the family. Three main clades were recognized within Ampelopsideae, corresponding to Ampelopsis, Nekemias, and the Southern Hemisphere lineage, respectively, and all with 100% bootstrap supports. The genome sequences and content of the tribe are highly conserved. However, comparative analyses suggested that the plastomes of Nekemias demonstrate a contraction in the large single copy region and an expansion in the inverted repeat region, and possess a high number of forward and palindromic repeat sequences distinct from both Ampelopsis and the Southern Hemisphere taxa.

CONCLUSIONS

Our results highlighted plastome variations in genome length, expansion or contraction of the inverted repeat region, codon usage bias, and repeat sequences, are corresponding to the three lineages of the tribe, which probably faced with different environmental selection pressures and evolutionary history. This study provides valuable insights into understanding the evolutionary patterns of plastid genomes within the Ampelopsideae of Vitaceae.

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.

Plastid phylogenomics of the tribe potentilleae (Rosaceae)

The tribe Potentilleae comprises approximately 1700 species in 13 genera, making it one of the largest of the 16 tribes in Rosaceae. Our understanding of the composition and relationships among members of Potentilleae has advanced dramatically with the application of molecular markers in the last two decades. Yet there is still much work remaining toward a robust phylogenetic framework for the entire Potentilleae and a comprehensive genus-level dating framework for the tribe. The goals of the present study were to establish a phylogenetic framework for Potentilleae, infer the origin and diversification of the tribe using a temporal framework, and explore the taxonomic implications in light of the updated phylogenetic framework. We used the plastome sequences from 158 accessions representing 139 taxa covering all 13 recognized genera of the tribe to reconstruct the Potentilleae phylogeny. High phylogenetic resolution was recovered along the Potentilleae backbone. Two major clades were recovered within Potentilleae, corresponding to the two subtribes Fragariinae and Potentillinae. Within Fragariinae, two subclades were recovered. In one subclade, Sibbaldia sensu stricto is sister to a clade containing Sibbaldianthe, Comarum, Farinopsis, and Alchemilla sensu lato. In the other subclade, Fragaria is sister to a clade comprising Chamaerhodos, Chamaecallis, Drymocallis, Dasiphora, and Potaninia. Within Potentillinae, Argentina is sister to Potentilla sensu stricto. Within Potentilla sensu stricto, clade Himalaya is sister to Alba, and the Himalaya-Alba clade together is sister to a clade comprising Reptans, Potentilla ancistrifolia Bunge, Fragarioides, Ivesioid, and Argentea. Divergence time estimates indicated that tribe Potentilleae originated during the middle Eocene, and subtribes Fragariinae and Potentillinae diverged around the Eocene-Oligocene transition, and divergence times dated for Potentilleae genera ranged from the early Miocene to the late Pleistocene.

Plastome phylogenomics and morphological traits analyses provide new insights into the phylogenetic position, species delimitation and speciation of Triplostegia (Caprifoliaceae)

BACKGROUND

The genus Triplostegia contains two recognized species, T. glandulifera and T. grandiflora, but its phylogenetic position and species delimitation remain controversial. In this study, we assembled plastid genomes and nuclear ribosomal DNA (nrDNA) cistrons sampled from 22 wild Triplostegia individuals, each from a separate population, and examined these with 11 recently published Triplostegia plastomes. Morphological traits were measured from herbarium specimens and wild material, and ecological niche models were constructed.

RESULTS

Triplostegia is a monophyletic genus within the subfamily Dipsacoideae comprising three monophyletic species, T. glandulifera, T. grandiflora, and an unrecognized species Triplostegia sp. A, which occupies much higher altitude than the other two. The new species had previously been misidentified as T. glandulifera, but differs in taproot, leaf, and other characters. Triplotegia is an old genus, with stem age 39.96 Ma, and within it T. glandulifera diverged 7.94 Ma. Triplostegia grandiflora and sp. A diverged 1.05 Ma, perhaps in response to Quaternary climate fluctuations. Niche overlap between Triplostegia species was positively correlated with their phylogenetic relatedness.

CONCLUSIONS

Our results provide new insights into the species delimitation of Triplostegia, and indicate that a taxonomic revision of Triplostegia is needed. We also identified that either rpoB-trnC or ycf1 could serve as a DNA barcode for Triplostegia.

Mitochondrial genome comparison and phylogenetic analysis of Dendrobium (Orchidaceae) based on whole mitogenomes

BACKGROUND

Mitochondrial genomes are essential for deciphering the unique evolutionary history of seed plants. However, the rules of their extreme variation in genomic size, multi-chromosomal structure, and foreign sequences remain unresolved in most plant lineages, which further hindered the application of mitogenomes in phylogenetic analyses.

RESULTS

Here, we took Dendrobium (Orchidaceae) which shows the great divergence of morphology and difficulty in species taxonomy as the study focus. We first de novo assembled two complete mitogenomes of Dendrobium wilsonii and Dendrobium henanense that were 763,005 bp and 807,551 bp long with multichromosomal structures. To understand the evolution of Dendrobium mitogenomes, we compared them with those of four other orchid species. The results showed great variations of repetitive and chloroplast-derived sequences in Dendrobium mitogenomes. Moreover, the intergenic content of Dendrobium mitogenomes has undergone expansion during evolution. We also newly sequenced mitogenomes of 26 Dendrobium species and reconstructed phylogenetic relationships of Dendrobium based on genomic mitochondrial and plastid data. The results indicated that the existence of chloroplast-derived sequences made the mitochondrial phylogeny display partial characteristics of the plastid phylogeny. Additionally, the mitochondrial phylogeny provided new insights into the phylogenetic relationships of Dendrobium species.

CONCLUSIONS

Our study revealed the evolution of Dendrobium mitogenomes and the potential of mitogenomes in deciphering phylogenetic relationships at low taxonomic levels.

Comprehensive Analysis of the Complete Chloroplast Genome of Cinnamomum daphnoides (Lauraceae), An Endangered Island Endemic Plant

Cinnamomum daphnoides (Siebold & Zucc 1846) is a rare and endangered island species with a unique Sino-Japanese distribution pattern. However, inormation regarding the species' chloroplast (cp) genome, structural features, and the phylogenetic relationship is still lacking. We utilized high-throughput sequencing technology to assemble and annotate the first cp genome of C. daphnoides (GenBank OR654104), followed by genomic characterization and phylogenetic analysis to fill the gaps in this species' cp genome. Our analysis showed that the cp genome has a quadripartite structure spanning 152,765 bp with a GC content of 39.15%. The genome encodes 126 genes, which include 36 tRNA genes, 8 rRNA genes, and 82 mRNA genes. Specifically, 44 genes are related to photosynthesis, 59 are associated with self-replication, six are other genes, and four have unknown functionality. The Codon usage bias in the genome exhibits a preference for A/U bases. We identified 29 interspaced repeat sequences that belonging to three types of repeat sequences. A total of 217 cpSSR loci were detected with single nucleotide repeats (59.91%) being the most frequent loci, mainly composed of A/T repeats. Our selection pressure analysis revealed that the ycf2 gene experienced strong positive selection (Ka/Ks = 1.81, P > 0.844). Further, we identified three highly variable fragments (psbM, psbT, and ycf1) that can be utilized as specific DNA barcoding markers for species definition and population genetic studies. We conducted boundary analysis, which showed that the structure and gene sequence of the two species were highly conserved. Finally, our phylogenetic analysis supports that C. daphnoides is close to C. cassia in the Cinnamomum genes, indicating that the two species share a common ancestry. Overall, providing genomic information on C. daphnoides will be beneficial for the conservation and utilization of endangered plant genetic resources. It will also serve as a reference for the identification of species and the phylogenetic analysis of Cinnamomum. This information will be useful in future research.

Extensive characterization of 28 complete chloroplast genomes of Hydrangea species: A perspective view of their organization and phylogenetic and evolutionary relationships

The tribe Hydrangeeae displays a unique, distinctive disjunct distribution encompassing East Asia, North America and Hawaii. Despite its complex trait variations and polyphyletic nature, comprehensive phylogenomic and biogeographical studies on this tribe have been lacking. To address this gap, we sequenced and characterized 28 plastomes of Hydrangeeae. Our study highlights the highly conserved nature of Hydrangeaceae chloroplast (cp) genomes in terms of gene content and arrangement. Notably, synapomorphic characteristics of tandem repeats in the conserved domain of accD were observed in the Macrophyllae, Chinenses, and Dichroa sections within the Hydrangeeae tribe. Additionally, we found lower expression of accD in these sections using structure prediction and quantitative real-time PCR analysis. Phylogenomic analyses revealed the subdivision of the Hydrangeeae tribe into two clades with robust support values. Consistent with polyphyletic relationships, sect. Broussaisia was identified as the basal group in the tribe Hydrangeeae. Our study also provides insights into the phylogenetic relationships of Hydrangea petiolaris in the Jeju and Ulleung Island populations, suggesting the need for further studies with more samples and molecular data. Divergence time estimation and biogeographical analyses suggested that the common ancestors of the tribe Hydrangeeae likely originated from North America and East Asia during the Paleocene period via the Bering Land Bridge, potentially facilitating migration within the tribe between these regions. In conclusion, this study enhances our understanding of the evolutionary history and biogeography of the tribe Hydrangeeae, shedding light on the dispersal patterns and origins of this intriguing plant group with its unique disjunct distribution.

Plastome evolution and phylogenomic insights into the evolution of Lysimachia (Primulaceae: Myrsinoideae)

BACKGROUND

Lysimachia L., the second largest genus within the subfamily Myrsinoideae of Primulaceae, comprises approximately 250 species worldwide. China is the species diversity center of Lysimachia, containing approximately 150 species. Despite advances in the backbone phylogeny of Lysimachia, species-level relationships remain poorly understood due to limited genomic information. This study analyzed 50 complete plastomes for 46 Lysimachia species. We aimed to identify the plastome structure features and hypervariable loci of Lysimachia. Additionally, the phylogenetic relationships and phylogenetic conflict signals in Lysimachia were examined.

RESULTS

These fifty plastomes within Lysimachia had the typical quadripartite structure, with lengths varying from 152,691 to 155,784 bp. Plastome size was positively correlated with IR and intron length. Thirteen highly variable regions in Lysimachia plastomes were identified. Additionally, ndhB, petB and ycf2 were found to be under positive selection. Plastid ML trees and species tree strongly supported that L. maritima as sister to subg. Palladia + subg. Lysimachia (Christinae clade), while the nrDNA ML tree clearly placed L. maritima and subg. Palladia as a sister group.

CONCLUSIONS

The structures of these plastomes of Lysimachia were generally conserved, but potential plastid markers and signatures of positive selection were detected. These genomic data provided new insights into the interspecific relationships of Lysimachia, including the cytonuclear discordance of the position of L. maritima, which may be the result of ghost introgression in the past. Our findings have established a basis for further exploration of the taxonomy, phylogeny and evolutionary history within Lysimachia.

Phylogeny of Trigonotis in China-with a special reference to its nutlet morphology and plastid genome

The genus Trigonotis comprises nearly 60 species mainly distributed in East and Southeast Asia. China has the largest number of Trigonotis species in the world, with a total of 44 species, of which 38 are endemic. Nutlet morphology is useful for the taxonomic delimitation of Trigonotis. However, there are still controversial circumscriptions of nutlet shape in some species. In previous studies, interspecies phylogenetic relationships were inferred using few DNA markers and very few taxa, which possibly led to erroneous or incomplete conclusions. In this study, the nutlet morphology of 39 Trigonotis taxa and the characteristics of 34 complete chloroplast genomes (29 taxa) were investigated and analyzed. Then, the phylogenetic relationships were discussed within this genus based on complete chloroplast genomes. To the best of our knowledge, this study is the first comprehensive analysis of nutlet morphology and complete chloroplast genome of Trigonotis. Based on nutlet morphology, Trigonotis can be divided into two groups: Group 1, hemispherical or oblique tetrahedron with carpopodiums, and Group 2, inverted tetrahedron without carpopodiums. The chloroplast genome of Trigonotis exhibited a typical quadripartite structure, including 84-86 protein-coding, 37 transfer RNA, and 8 ribosomal RNA genes, with a total length of 147,247-148,986 bp. Genes in the junctions were well conserved in Trigonotis, similar to those in other Boraginaceae s.str. species. Furthermore, Trigonotis chloroplast genomes showed relatively high diversity, with more conserved genic regions than intergenic regions; in addition, we detected 14 hot spots (Pi > 0.005) in non-coding regions. Phylogenetic analyses based on chloroplast genome data identified highly resolved relationships between Trigonotis species. Specifically, Trigonotis was divided into two clades with strong support: one clade included species with hemispherical or oblique tetrahedron nutlets with carpopodiums and bracts, whereas the other clade included species with inverted tetrahedron nutlets without carpopodiums or bracts. Our results may inform future taxonomic, phylogenetic, and evolutionary studies on Boraginaceae.

Characteristics of plastid genomes in the genus Ceratostigma inhabiting arid habitats in China and their phylogenomic implications

BACKGROUND

Ceratostigma, a genus in the Plumbaginaceae, is an ecologically dominant group of shrubs, subshrub and herb mainly distributed in Qinghai-Tibet Plateau and North China. Ceratostigma has been the focal group in several studies, owing to their importance in economic and ecological value and unique breeding styles. Despite this, the genome information is limited and interspecific relationships within the genus Cerotastigma remains unexplored. Here we sequenced, assembled and characterized the 14 plastomes of five species, and conducted phylogenetic analyses of Cerotastigma using plastomes and nuclear ribosomal DNA (nrDNA) data.

RESULTS

Fourteen Cerotastigma plastomes possess typical quadripartite structures with lengths from 164,076 to 168,355 bp that consist of a large single copy, a small single copy and a pair of inverted repeats, and contain 127-128 genes, including 82-83 protein coding genes, 37 transfer RNAs and eight ribosomal RNAs. All plastomes are highly conservative and similar in gene order, simple sequence repeats (SSRs), long repeat repeats and codon usage patterns, but some structural variations in the border of single copy and inverted repeats. Mutation hotspots in coding (Pi values > 0.01: matK, ycf3, rps11, rps3, rpl22 and ndhF) and non-coding regions (Pi values > 0.02: trnH-psbA, rps16-trnQ, ndhF-rpl32 and rpl32-trnL) were identified among plastid genomes that could be served as potential molecular markers for species delimitation and genetic variation studies in Cerotastigma. Gene selective pressure analysis showed that most protein-coding genes have been under purifying selection except two genes. Phylogenetic analyses based on whole plastomes and nrDNA strongly support that the five species formed a monophyletic clade. Moreover, interspecific delimitation was well resolved except C. minus, individuals of which clustered into two main clades corresponding to their geographic distributions. The topology inferred from the nrDNA dataset was not congruent with the tree derived from the analyses of the plastid dataset.

CONCLUSION

These findings represent the first important step in elucidating plastome evolution in this widespread distribution genus Cerotastigma in the Qinghai-Tibet Plateau. The detailed information could provide a valuable resource for understanding the molecular dynamics and phylogenetic relationship in the family Plumbaginaceae. Lineage genetic divergence within C. minus was perhaps promoted by geographic barriers in the Himalaya and Hengduan Mountains region, but introgression or hybridization could not be completely excluded.

Insights into cryptic speciation of quillworts in China

Cryptic species are commonly misidentified because of high morphological similarities to other species. One group of plants that may harbor large numbers of cryptic species is the quillworts (Isoëtes spp.), an ancient aquatic plant lineage. Although over 350 species of Isoëtes have been reported globally, only ten species have been recorded in China. The aim of this study is to better understand Isoëtes species diversity in China. For this purpose, we systematically explored the phylogeny and evolution of Isoëtes using complete chloroplast genome (plastome) data, spore morphology, chromosome number, genetic structure, and haplotypes of almost all Chinese Isoëtes populations. We identified three ploidy levels of Isoëtes in China-diploid (2n = 22), tetraploid (2n = 44), and hexaploid (2n = 66). We also found four megaspore and microspore ornamentation types in diploids, six in tetraploids, and three in hexaploids. Phylogenetic analyses confirmed that I. hypsophila as the ancestral group of the genus and revealed that Isoëtes diploids, tetraploids, and hexaploids do not form monophyletic clades. Most individual species possess a single genetic structure; however, several samples have conflicting positions on the phylogenetic tree based on SNPs and the tree based on plastome data. All 36 samples shared 22 haplotypes. Divergence time analysis showed that I. hypsophila diverged in the early Eocene (∼48.05 Ma), and most other Isoëtes species diverged 3-20 Ma. Additionally, different species of Isoëtes were found to inhabit different water systems and environments along the Yangtze River. These findings provide new insights into the relationships among Isoëtes species in China, where highly similar morphologic populations may harbor many cryptic species.

Characterization of the complete plastid genome of Korean endemic, Ajuga spectabilis Nakai (Lamiaceae)

Ajuga spectabilis Nakai is a Korean endemic species in Lamiaceae. In spite of its importance, genomic studies are not performed on this species. Here, we report the complete plastid genome sequences of A. spectabilis, which will provide valuable information for its natural conservation and future studies for the plastid genome evolution. The plastid genome is 150,417 bp in length, containing a large single-copy region (LSC) of 82,140 bp and a small single-copy (SSC) region of 17,165 bp which are separated by a pair of inverted repeats (IR) of 25,556 bp. It encodes 113 genes, including 79 protein-coding genes, 30 tRNA genes, and four rRNA genes. The overall GC content is 38.3%, and those in the LSC, SSC, and IR regions are 36.4%, 32.2%, and 43.3%, respectively, which is consistent with other Ajuga species. Our phylogenetic analysis revealed that A. spectabilis formed a close relationship with A. ciliata and A. decumbens.

CPJSdraw: analysis and visualization of junction sites of chloroplast genomes

Background

Chloroplast genomes are usually circular molecules, and most of them are tetrad structures with two inverted repeat (IR) regions, a large single-copy region, and a small single-copy region. IR contraction and expansion are among the genetic diversities during the evolution of plant chloroplast genomes. The only previously released tool for the visualization of junction sites of the regions does not consider the diversity of the starting point of genomes, which leads to incorrect results or even no results for the examination of IR contraction and expansion.

Results

In this work, a new tool named CPJSdraw was developed for visualizing the junction sites of chloroplast genomes. CPJSdraw can format the starting point of the irregular linearized genome, correct the junction sites of IR and single-copy regions, display the tetrad structure, visualize the junction sites of any number (≥1) of chloroplast genomes, show the transcription direction of genes adjacent to junction sites, and indicate the IR expansion or contraction of chloroplast genomes.

Conclusions

CPJSdraw is a software that is universal and reliable in analysis and visualization of IR expansion or contraction of chloroplast genomes. CPJSdraw has more accurate analysis and more complete functions when compared with previously released tool. CPJSdraw as a perl package and tested data are available at http://dx.doi.org/10.5281/zenodo.7669480 for English users. In addition, an online version with a Chinese interface is available at http://cloud.genepioneer.com:9929/#/tool/alltool/detail/335.

Comparative plastomes and phylogenetic analysis of seven Korean endemic Saussurea (Asteraceae)

BACKGROUND

Saussurea is one of the most species-rich genera in the Cardueae, Asteraceae. There are approximately 40 Saussurea species distributed in Korea, with nearly 40% of them endemics. Infrageneric relationships remain uncertain due to insufficient resolutions and low statistical support. In this study, we sequenced the plastid genomes of five Korean endemic Saussurea (S. albifolia, S. calcicola, S. diamantica, S. grandicapitula, and S. seoulensis), and comparative analyses including two other endemics (S. chabyoungsanica and S. polylepis) were conducted.

RESULTS

The plastomes of Korean endemics were highly conserved in gene content, order, and numbers. Exceptionally, S. diamantica had mitochondrial DNA sequences including two tRNAs in SSC region. There were no significant differences of the type and numbers of SSRs among the seven Korean endemics except in S. seoulensis. Nine mutation hotspots with high nucleotide diversity value (Pi > 0.0033) were identified, and phylogenetic analysis suggested that those Korean endemic species most likely evolved several times from diverse lineages within the genus. Moreover, molecular dating estimated that the Korean endemic species diverged since the late Miocene.

CONCLUSIONS

This study provides insight into understanding the plastome evolution and evolutionary relationships of highly complex species of Saussurea in Korean peninsula.

Complete chloroplast genome of Boesenbergia rotunda and a comparative analysis with members of the family Zingiberaceae

Boesenbergia rotunda (L.) Mansf. is a medically important ginger species of the family Zingiberaceae but its genomic information on molecular phylogeny and identification is scarce. In this work, the chloroplast genome of B. rotunda was sequenced, characterized and compared to the other Zingiberaceae species to provide chloroplast genetic resources and to determine its phylogenetic position in the family. The chloroplast genome of B. rotunda was 163,817 bp in length and consisted of a large single-copy (LSC) region of 88,302 bp, a small single-copy (SSC) region of 16,023 bp and a pair of inverted repeats (IRA and IRB) of 29,746 bp each. The chloroplast genome contained 113 unique genes, including 79 protein-coding genes, 30 transfer RNA (tRNA) genes and four ribosomal RNA (rRNA) genes. Several genes had atypical start codons, while most amino acids exhibited biased usage of synonymous codons. Comparative analyses with various chloroplast genomes of Zingiberaceae taxa revealed several highly variable regions (psbK-psbI, trnT-GGU-psbD, rbcL-accD, ndhF-rpl32, and ycf1) in the LSC and SSC regions in the chloroplast genome of B. rotunda that could be utilized as molecular markers for DNA barcoding and species delimitation. Phylogenetic analyses based on shared protein-coding genes revealed that B. rotunda formed a distinct lineage with B. kingii Mood & L.M.Prince, in a subclade that also contained the genera Kaempferia and Zingiber. These findings constitute the first chloroplast genome information of B. rotunda that could be a reference for phylogenetic analysis and identification of genus Boesenbergia within the Zingiberaceae family.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s40415-022-00845-w.

Complete plastid genome of Lespedeza tricolor (Fabaceae), an endemic shrub in Korea

Lespedeza tricolor is a species found in the southern province of Korea, thought to be endemic to Korea. The complete plastid genome of this legume was sequenced in this study. DNA from L. tricolor was extracted, sequenced, and assembled into the complete plastid genome. We used 18 species of the family Fabaceae and 77 protein-coding genes to perform phylogenetic analysis. The plastid genome is 149,038 bp in length, with large (82,495 bp) and small (18,889 bp) single-copy regions, separated by a pair of inverted repeat regions (23,827 bp). It contains 83 protein-coding genes, eight rRNAs, 37 tRNAs, and two pseudogenes (rpl22 and infA). Our phylogenetic analysis suggests that the genus Lespedeza is monophyletic and L. tricolor is closely related to L. maritima and L. buergeri. In this study, we identified the phylogenetic position of L. tricolor and provided the data that can be used in various ways in future studies.

Comparing complete organelle genomes of holoparasitic Christisonia kwangtungensis (Orabanchaceae) with its close relatives: how different are they?

BACKGROUND

Orobanchaceae is the only flowering plant family with species from free-living nonparasite, hemi-parasite to holoparasite, making it an ideal system for studying the evolution of parasitism. However, both plastid and mitochondrial genome have been sequenced in only few parasitic species in Orobanchaceae. Therefore, further comparative study is wanted to investigate the impact of holoparasitism on organelle genomes evolution between close relatives. Here, we sequenced organelle genomes and transcriptome of holoparasitic Christisonia kwangtungensis and compared it with its closely related groups to analyze similarities and differences in adaption strategies to the holoparasitic lifestyle.

RESULTS

The plastid genome of C. kwangtungensis has undergone extensive pseudogenization and gene loss, but its reduction pattern is different from that of Aeginetia indica, the close relative of C. kwangtungensis. Similarly, the gene expression detected in the photosynthetic pathway of these two genera is different. In Orobanchaceae, holoparasites in Buchnereae have more plastid gene loss than Rhinantheae, which reflects their longer history of holoparasitism. Distinct from severe degradation of the plastome, protein-coding genes in the mitochondrial genome of C. kwangtungensis are relatively conserved. Interestingly, besides intracellularly transferred genes which are still retained in its plastid genome, we also found several horizontally transferred genes of plastid origin from diverse donors other than their current hosts in the mitochondrial genome, which probably indicate historical hosts.

CONCLUSION

Even though C. kwangtungensis and A. indica are closely related and share severe degradation of plastome, they adapt organelle genomes to the parasitic lifestyle in different ways. The difference between their gene loss and gene expression shows they ultimately lost photosynthetic genes but through different pathways. Our study exemplifies how parasites part company after achieving holoparasitism.

A new lineage of non-photosynthetic green algae with extreme organellar genomes

Background

The plastid genomes of the green algal order Chlamydomonadales tend to expand their non-coding regions, but this phenomenon is poorly understood. Here we shed new light on organellar genome evolution in Chlamydomonadales by studying a previously unknown non-photosynthetic lineage. We established cultures of two new Polytoma-like flagellates, defined their basic characteristics and phylogenetic position, and obtained complete organellar genome sequences and a transcriptome assembly for one of them.

Results

We discovered a novel deeply diverged chlamydomonadalean lineage that has no close photosynthetic relatives and represents an independent case of photosynthesis loss. To accommodate these organisms, we establish the new genus Leontynka, with two species (L. pallida and L. elongata) distinguishable through both their morphological and molecular characteristics. Notable features of the colourless plastid of L. pallida deduced from the plastid genome (plastome) sequence and transcriptome assembly include the retention of ATP synthase, thylakoid-associated proteins, the carotenoid biosynthesis pathway, and a plastoquinone-based electron transport chain, the latter two modules having an obvious functional link to the eyespot present in Leontynka. Most strikingly, the ~362 kbp plastome of L. pallida is by far the largest among the non-photosynthetic eukaryotes investigated to date due to an extreme proliferation of sequence repeats. These repeats are also present in coding sequences, with one repeat type found in the exons of 11 out of 34 protein-coding genes, with up to 36 copies per gene, thus affecting the encoded proteins. The mitochondrial genome of L. pallida is likewise exceptionally large, with its >104 kbp surpassed only by the mitogenome of Haematococcus lacustris among all members of Chlamydomonadales hitherto studied. It is also bloated with repeats, though entirely different from those in the L. pallida plastome, which contrasts with the situation in H. lacustris where both the organellar genomes have accumulated related repeats. Furthermore, the L. pallida mitogenome exhibits an extremely high GC content in both coding and non-coding regions and, strikingly, a high number of predicted G-quadruplexes.

Conclusions

With its unprecedented combination of plastid and mitochondrial genome characteristics, Leontynka pushes the frontiers of organellar genome diversity and is an interesting model for studying organellar genome evolution.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-022-01263-w.

Unprecedented organelle genomic variations in morning glories reveal independent evolutionary scenarios of parasitic plants and the diversification of plant mitochondrial complexes

Background

The morning glories (Convolvulaceae) are distributed worldwide and produce economically important crops, medicinal herbs, and ornamentals. Members of this family are diverse in morphological characteristics and trophic modes, including the leafless parasitic Cuscuta (dodders). Organelle genomes were generally used for studying plant phylogeny and genomic variations. Notably, plastomes in parasitic plants always show non-canonical features, such as reduced size and accelerated rates. However, few organelle genomes of this group have been sequenced, hindering our understanding of their evolution, and dodder mitogenome in particular.

Results

We assembled 22 new mitogenomes and 12 new plastomes in Convolvulaceae. Alongside previously known ones, we totally analyzed organelle genomes of 23 species in the family. Our sampling includes 16 leafy autotrophic species and 7 leafless parasitic dodders, covering 8 of the 12 tribes. Both the plastid and mitochondrial genomes of these plants have encountered variations that were rarely observed in other angiosperms. All of the plastomes possessed atypical IR boundaries. Besides the gene and IR losses in dodders, some leafy species also showed gene and intron losses, duplications, structural variations, and insertions of foreign DNAs. The phylogeny reconstructed by plastid protein coding sequences confirmed the previous relationship of the tribes. However, the monophyly of ‘Merremieae’ and the sister group of Cuscuta remained uncertain. The mitogenome was significantly inflated in Cuscuta japonica, which has exceeded over 800 kb and integrated massive DNAs from other species. In other dodders, mitogenomes were maintained in small size, revealing divergent evolutionary strategies. Mutations unique to plants were detected in the mitochondrial gene ccmFc, which has broken into three fragments through gene fission and splicing shift. The unusual changes likely initially happened to the common ancestor of the family and were caused by a foreign insertion from rosids followed by double-strand breaks and imprecise DNA repairs. The coding regions of ccmFc expanded at both sides after the fission, which may have altered the protein structure.

Conclusions

Our family-scale analyses uncovered unusual scenarios for both organelle genomes in Convolvulaceae, especially in parasitic plants. The data provided valuable genetic resources for studying the evolution of Convolvulaceae and plant parasitism.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-022-01250-1.

The complete plastid genome sequence of the enigmatic moss, Takakia lepidozioides (Takakiopsida, Bryophyta): evolutionary perspectives on the largest collection of genes in mosses and the intensive RNA editing

Complete chloroplast genome sequence of a moss, Takakia lepidozioides (Takakiopsida) is reported. The largest collection of genes in mosses and the intensive RNA editing were discussed from evolutionary perspectives. We assembled the entire plastid genome sequence of Takakia lepidozioides (Takakiopsida), emerging from the first phylogenetic split among extant mosses. The genome sequences were assembled into a circular molecule 149,016 bp in length, with a quadripartite structure comprising a large and a small single-copy region separated by inverted repeats. It contained 88 genes coding for proteins, 32 for tRNA, four for rRNA, two open reading frames, and at least one pseudogene (tufA). This is the largest number of genes of all sequenced plastid genomes in mosses and Takakia is the only moss that retains the seven coding genes ccsA, cysA, cysT, petN rpoA, rps16 and trnP^GGG. Parsimonious interpretation of gene loss suggests that the last common ancestor of bryophytes had all seven genes and that mosses lost at least three of them during their diversification. Analyses of the plastid transcriptome identified the extraordinary frequency of RNA editing with more than 1100 sites. We indicated a close correlation between the monoplastidy of vegetative tissue and the intensive RNA editing sites in the plastid genome in land plant lineages. Here, we proposed a hypothesis that the small population size of plastids in each vegetative cell of some early diverging land plants, including Takakia, might cause the frequent fixation of mutations in plastid genome through the intracellular genetic drift and that deleterious mutations might be continuously compensated by RNA editing during or following transcription.

Comparative plastid genomics of Mazaceae: focusing on a new recognized genus, Puchiumazus

Six Mazaceae plastomes were assembled in this study, including the newly recognized genus, Puchiumazus. Comparative plastid genomic analysis provided new insights into Mazaceae. The phylogenetic categorization of Mazus lanceifolius (Mazaceae) has long been uncertain. In 2021, the scholars Bo Li, D. G. Zhang, and C. L. Xiang republished M. lanceifolius as a new species Puchiumazus lanceifolius, within a new genus Puchiumazus. However, there is little plastome information on Mazaceae. Following the publishing of the new genus Puchiumazus, it is now necessary to study the Mazaceae plastome features to comprehensively understand this young family. The Mazaceae plastomes all have a typical quartile structure. The plastomes have a size ranging from 152,388 to 154,252 bp, and each plastome contains 112 unique genes, including 78 protein-coding genes, 4 rRNA genes, and 30 tRNA genes. A comparative analysis showed that these plastome sequences are highly conserved. Furthermore, we identified four relatively hypervariable regions (trnQ-UUC-psbK, trnS-GCU- trnS-CGA, trnT-UGU-trnL-UAA and ycf1) that can be used as potential DNA barcodes for the identification of this clade. Phylogenetic relationships based on the whole plastome sequences of 25 samples of 14 genera of Lamiales placed M. lanceifolius in the basal clade of the family Mazaceae, with 100% bootstrap support. In summary, the M. lanceifolius results indicate that a new monotype genus (Puchiumazus) should be established at the whole-plastome level. This study provides plastid genomic resources for exploring the phylogeny of Mazaceae.

An updated phylogenetic and biogeographic analysis based on genome skimming data reveals convergent evolution of shrubby habit in Clematis in the Pliocene and Pleistocene

Convergent evolution, often viewed as the inevitable outcome of natural selection, has received special attention since the time of Darwin. Clematis is well known for its climbing habit, but it has some shrubby species, known as sect. Fruticella s.l. The shrubby Clematis species are distributed in the dry habitats of Central Asia and adjacent areas showing possible convergent evolution. In this study, we assembled the complete plastome and nuclear ribosomal DNA (nrDNA) sequences of 56 Clematis species, representing most sections and covering most of the shrubby species, to reconstruct their evolutionary histories. Using both maximum likelihood and Bayesian methods, the plastome and nrDNA datasets generated similar, but not identical, phylogenetic relationships, which are better resolved than in previous studies. Then, molecular dating, historical range reconstruction, and character optimization analyses were conducted based on this updated phylogenetic framework. All the morphological characters widely used for taxonomy were shown to have evolved multiple times. Molecular dating inferred that Clematis diverged from its sister in the mid Miocene, and all six major clades of Clematis originated during the late Miocene, with a species radiation during the Pliocene to Pleistocene. The results clearly showed that the shrubby habit evolved independently in four lineages of Clematis in Asia. We also revealed that the shrubby lineages have emerged since the very beginning of Pliocene. Asian monsoon variation in the Pliocene and glacial period fluctuation in the Pleistocene may be the driving forces for the origin and diversification of the shrubby Clematis in Central Asia and adjacent dry areas.

The complete chloroplast genome of Artocarpus altilis (Moraceae) and phylogenetic relationships

The chloroplast (cp) is an essential organelle in higher plants. The genes of the plastome are well suited to infer phylogenetic relationships among taxa. In this study, we report the assembly of the cp genome of Artocarpus altilis and its phylogeny among species from Moraceae family. The cp genome of A. altilis was 160,822 base pair (bp) in length, comprising one large single-copy region of 88,692 bp, one small single-copy region of 19,290 bp, and a pair of inverted repeat regions (IRs) of 26,420 bp. A total of 113 different genes were predicted, including 79 protein-coding genes, 30 tRNA genes, and four rRNA genes. The phylogenetic analysis of 19 species belonging to the Moraceae family confirmed the phylogenetic proximity of the genus Artocarpus and Morus and the genetic similarity of A. camansi and A. altilis.

Discordant evolution of organellar genomes in peas (Pisum L.)

Plastids and mitochondria have their own small genomes, which do not undergo meiotic recombination and may have evolutionary fates different from each other and that of the nuclear genome. For the first time, we sequenced mitochondrial genomes of pea (Pisum L.) from 42 accessions mostly representing diverse wild germplasm from throughout the wild pea geographical range. Six structural types of the pea mitochondrial genome were revealed. From the same accessions, plastid genomes were sequenced. Phylogenetic trees based on the plastid and mitochondrial genomes were compared. The topologies of these trees were highly discordant, implying not less than six events of hybridisation between diverged wild peas in the past, with plastids and mitochondria differently inherited by the descendants. Such discordant inheritance of organelles could have been driven by plastid-nuclear incompatibility, which is known to be widespread in crosses involving wild peas and affects organellar inheritance. The topology of the phylogenetic tree based on nucleotide sequences of a nuclear gene, His5, encoding a histone H1 subtype, corresponded to the current taxonomy and resembled that based on the plastid genome. Wild peas (Pisum sativum subsp. elatius s.l.) inhabiting Southern Europe were shown to be of hybrid origin, resulting from crosses of peas related to those presently inhabiting the eastern Mediterranean in a broad sense. These results highlight the roles of hybridisation and cytonuclear conflict in shaping plant microevolution.

Complete plastid genome of Cumathamnion serrulatum (Ceramiales, Rhodophyta)

We report the complete plastid genome of Cumathamnion serrulatum, also known as Delesseria serrulata. The plastid genome was 174,192 bp in size. Annotation showed there were 193 protein coding genes, three ribosomal RNAs, and 29 transfer RNAs. One intron was found, and the GC content was 27.2%. The maximum likelihood tree with the concatenated 177 plastid coding genes showed a strong monophyletic relationship to Membranoptera spp. within the Ceramiales.

Elatostema qinzhouense (Urticaceae), a new species from limestone karst in Guangxi, China

Elatostema qinzhouense L.F. Fu, A.K. Monro & Y.G. Wei, a new species from Guangxi, China is described and illustrated. Morphologically, E. qinzhouense is most similar to E. hezhouense from which it differs by having smaller size of leaf laminae, fewer and smaller staminate peduncle bracts, longer pistillate peduncle bracts and a larger achene. This result is supported by the molecular evidence. The phylogenetic position of the new species within Elatostema is evaluated using three DNA regions, ITS, trnH-psbA and psbM-trnD, for 107 taxa of Elatostema s.l. (including E. qinzhouense). Bayesian inference (BI) and maximum likelihood (ML) analyses each recovered the same strongly supported tree topologies, indicating that E. qinzhouense is a member of the core Elatostema clade and sister to E. hezhouense. Along with the phylogenetic studies, plastid genome and ribosomal DNA (rDNA) sequences of the new species are assembled and annotated. The plastid genome is 150,398 bp in length and comprises two inverted repeats (IRs) of 24,688 bp separated by a large single-copy of 83,919 bp and a small single-copy of 17,103 bp. A total of 113 functional genes are recovered, comprising 79 protein-coding genes, 30 tRNA genes, and four rRNA genes. The rDNA is 5,804 bp in length and comprised the 18S ribosomal RNA partial sequence (1,809 bp), internal transcribed spacer 1 (213 bp), 5.8S ribosomal RNA (164 bp), internal transcribed spacer 2 (248 bp) and 26S ribosomal RNA partial sequence (3,370 bp). In addition, the chromosome number of E. qinzhouense is observed to be 2n = 26, suggesting that the species is diploid. Given a consistent relationship between ploidy level and reproductive system in Elatostema, the new species is also considered to be sexually reproducing. Our assessment of the extinction threat for E. qinzhouense is that it is Endangered (EN) according to the criteria of the International Union for Conservation of Nature.

Comparative analysis of complete plastid genomes from Lilium lankongense Franchet and its closely related species and screening of Lilium-specific primers

Lilium lankongense Franchet is a lily species found on the Qinghai-Tibet Plateau. It is pink with deep red spots, has a high ornamental value, and is used in hybrid breeding of horticultural lily varieties. We have insufficient knowledge of the genetic resources of L. lankongense and its phylogenetic relationships with related species. Recent molecular phylogenetic studies have shown a very close phylogenetic relationship between L. lankongense and the five species L. duchartrei, L. stewartianum, L. matangense, L. lophophorum, and L. nanum. However, molecular markers still lack sufficient signals for population-level research of the genus Lilium. We sequenced and compared the complete plastid sequences of L. lankongense and its five related species. The genomes ranged from 152,307 bp to 152,611 bp. There was a slight inconsistency detected in inverted repeat and single copy boundaries and there were 53 to 63 simple sequence repeats in the six species. Two of the 12 highly variable regions (trnC-petN and rpl32-trnL) were verified in 11 individuals and are promising for population-level studies. We used the complete sequence of 33 plastid genomes, the protein-coding region sequence, and the nuclear ITS sequence to reconstruct the phylogenetic tree of Lilium species. Our results showed that the plastid gene tree and nuclear gene tree were not completely congruent, which may be caused by hybridization, insufficient information contained in the nuclear ITS, or the small number of samples. The results of phylogenetic analysis based on plastid genomes indicated that the six Lilium species were closely related. Our study provides a preliminarily rebuilt backbone phylogeny that is significant for future molecular and morphological studies of Lilium.

Complete chloroplast genome sequence of Passiflora serrulata Jacq. (Passifloraceae)

This study was the first report for the complete chloroplast genome of Passiflora serrulata Jacq. (Passifloraceae). The cp genome was 149,683 bp in length contained two inverted repeats (IRs) of 25,470 bp, which were separated by large single-copy (LSC) and small single-copy (SSC) of 86,252 bp and 13,491 bp, respectively. A total of 110 functional genes were encoded, comprised 76 protein-coding genes, 30 tRNA genes, and four rRNA genes. The GC content was 37.0%. The maximum likelihood phylogenetic tree indicated that P. serrulata was recovered as the member of subg. Passiflora and most closely related to the clade formed by P. serratodigitata and P. ligularis.

Comparative plastid genomics of four Pilea (Urticaceae) species: insight into interspecific plastid genome diversity in Pilea

BACKGROUND

Pilea is a genus of perennial herbs from the family Urticaceae, and some species are used as courtyard ornamentals or for medicinal purposes. At present, there is no information about the plastid genome of Pilea, which limits our understanding of this genus. Here, we report 4 plastid genomes of Pilea taxa (Pilea mollis, Pilea glauca 'Greizy', Pilea peperomioides and Pilea serpyllacea 'Globosa') and performed comprehensive comparative analysis.

RESULTS

The four plastid genomes all have a typical quartile structure. The lengths of the plastid genomes ranged from 150,398 bp to 152,327 bp, and each genome contained 113 unique genes, including 79 protein-coding genes, 4 rRNA genes, and 30 tRNA genes. Comparative analysis showed a rather high level of sequence divergence in the four genomes. Moreover, eight hypervariable regions were identified (petN-psbM, psbZ-trnG-GCC, trnT-UGU-trnL-UAA, accD-psbI, ndhF-rpl32, rpl32-trnL-UAG, ndhA-intron and ycf1), which are proposed for use as DNA barcode regions. Phylogenetic relationships based on the plastid genomes of 23 species of 14 genera of Urticaceae resulted in the placement of Pilea in the middle and lower part of the phylogenetic tree, with 100% bootstrap support within Urticaceae.

CONCLUSION

Our results enrich the resources concerning plastid genomes. Comparative plastome analysis provides insight into the interspecific diversity of the plastid genome of Pilea. The identified hypervariable regions could be used for developing molecular markers applicable in various research areas.

Changes in plastid biogenesis leading to the formation of albino regenerants in barley microspore culture

BACKGROUND

Microspore embryogenesis is potentially the most effective method of obtaining doubled haploids (DH) which are utilized in breeding programs to accelerate production of new cultivars. However, the regeneration of albino plants significantly limits the exploitation of androgenesis for DH production in cereals. Despite many efforts, the precise mechanisms leading to development of albino regenerants have not yet been elucidated. The objective of this study was to reveal the genotype-dependent molecular differences in chloroplast differentiation that lead to the formation of green and albino regenerants in microspore culture of barley.

RESULTS

We performed a detailed analysis of plastid differentiation at successive stages of androgenesis in two barley cultivars, 'Jersey' and 'Mercada' that differed in their ability to produce green regenerants. We demonstrated the lack of transition from the NEP-dependent to PEP-dependent transcription in plastids of cv. 'Mercada' that produced mostly albino regenerants in microspore culture. The failed NEP-to-PEP transition was associated with the lack of activity of Sig2 gene encoding a sigma factor necessary for transcription of plastid rRNA genes. A very low level of 16S and 23S rRNA transcripts and impaired plastid translation machinery resulted in the inhibition of photomorphogenesis in regenerating embryos and albino regenerants. Furthermore, the plastids present in differentiating 'Mercada' embryos contained a low number of plastome copies whose replication was not always completed. Contrary to 'Mercada', cv. 'Jersey' that produced 90% green regenerants, showed the high activity of PEP polymerase, the highly increased expression of Sig2, plastid rRNAs and tRNAGlu, which indicated the NEP inhibition. The increased expression of GLKs genes encoding transcription factors required for induction of photomorphogenesis was also observed in 'Jersey' regenerants.

CONCLUSIONS

Proplastids present in microspore-derived embryos of albino-producing genotypes did not pass the early checkpoints of their development that are required for induction of further light-dependent differentiation of chloroplasts. The failed activation of plastid-encoded RNA polymerase during differentiation of embryos was associated with the genotype-dependent inability to regenerate green plants in barley microspore culture. The better understanding of molecular mechanisms underlying formation of albino regenerants may be helpful in overcoming the problem of albinism in cereal androgenesis.

DNA barcoding and molecular phylogeny of Dumasia (Fabaceae: Phaseoleae) reveals a cryptic lineage

Dumasia taxonomy and classification have long been problematic. Species within this genus have few morphological differences and plants without flowers or fruits are difficult to accurately identify. In this study, we evaluated the ability of six DNA barcoding sequences, one nuclear (ITS) and five chloroplast regions (trnH-psbA, matK, rbcL, trnL-trnF, psbB-psbF), to efficiently identify Dumasia species. Most single markers or their combinations identify obvious barcoding gaps between intraspecific and interspecific genetic variation. Most combined analyses including ITS showed good species resolution and identification efficiency. We therefore suggest that ITS alone or a combination of ITS with any cpDNA marker are most suitable for DNA barcoding of Dumasia. The phylogenetic analyses clearly indicated that Dumasia yunnanensis is not monophyletic and is separated as two independent branches, which may result from cryptic differentiation. Our results demonstrate that molecular data can deepen the comprehension of taxonomy of Dumasia and provide an efficient approach for identification of the species.

The complete plastid genome of Ficus erecta (Moraceae)

Ficus erecta is a wild relative of F. carica, which is an important economic plant. Here, we determined the complete plastid genome of F. erecta using the Illumina paired reads to provide genomic feature resources. The whole plastid genome of F. erecta is 160,603 bp in length, containing two inverted repeats (IRs) of 25,899 bp separated by a large single-copy (LSC 88,640 bp) region and a small single-copy (SSC 20,165 bp) region. The complete plastome sequence of Ficus erecta will provide a useful resource for the evolutionary biology study as well as for the phylogenetic studies.

The complete chloroplast genome of Akebia trifoliata subsp. australis (Lardizabalaceae), a medicinal plant in China

Akebia trifoliata subsp. australis (Diels) T.Shimizu is a medicinal plant in China. Here, the complete chloroplast (cp) genome sequence of A. trifoliata subsp. australis was assembled and characterized as a resource for future genetic studies. The whole cp genome was 157,952 bp in length, containing of a large single-copy (LSC) region of 86,596 bp, a small single-copy (SSC) region of 19,060 bp, and two inverted repeat (IR) regions of 26,148 bp. The new sequence possessed total 113 unique genes, including 79 protein-coding genes, 30 tRNA genes and 4 rRNA genes. The nucleotide composition was asymmetric (30.3% A, 19.7% C, 19.0% G and 31.0% T) with an overall GC content of 38.7%. The maximum likelihood phylogenetic analysis based on 10 cp genomes indicated that A. trifoliata subsp. australis was closely related to Akebia trifoliata subsp. trifoliata. However, Akebia quinata was closely related to Stauntonia obovatifoliola.

Phylogeny of Euclidieae (Brassicaceae) based on plastome and nuclear ribosomal DNA data

Euclidieae, a morphologically diverse tribe in the family Brassicaceae (Cruciferae), consists of 29 genera and more than 150 species distributed mainly in Asia. Prior phylogenetic analyses on Euclidieae are inadequate. In this study, sequence data from the plastid genome and nuclear ribosomal DNA of 72 species in 27 genera of Euclidieae were used to infer the inter- and intra-generic relationships within. The well-resolved and strongly supported plastome phylogenies revealed that Euclidieae could be divided into five clades. Both Cymatocarpus and Neotorularia are polyphyletic in nuclear and plastome phylogenies. Besides, the conflicts of systematic positions of three species of Braya and two species of Solms-laubachia s.l. indicated that hybridization and or introgression might have happened during the evolutionary history of the tribe. Results from divergence-time analyses suggested an early Miocene origin of Euclidieae, and it probably originated from the Central Asia, Pamir Plateau and West Himalaya. In addition, multiple ndh genes loss and pseudogenization were detected in eight species based on comparative genomic study.

Comparison of eight complete plastid genomes from three moss families Amblystegiaceae, Calliergonaceae and Pylaisiaceae

We sequenced and assembled eight complete plastid genomes from three closely related pleurocarpous moss families: Amblystegium serpens, Campyliadelphus stellatus, Cratoneuron filicinum, Drepanocladus aduncus, and Leptodictyum humile (Amblystegiaceae), Calliergon sarmentosum and Warnstorfia exannulata (Calliergonaceae), and Calliergonella cuspidata (Pylaisiaceae). The newly generated plastid genomes range from 124,256 to 124,819 bp, with two inverted repeat regions (9,624–9,696 bp) separated by a large single-copy region (86,422–86,924 bp) and a small single-copy region (18,430–18,514 bp). All these plastid genomes encode 116 unique genes including 82 protein-coding genes, 30 tRNA genes and four rRNAgenes. The overall GC content is between 28.6%–29.3%. Phylogenetic analysis showed that all Amblystegiaceae species Amblystegium serpens, Campyliadelphus stellatus, Cratoneuron filicinum, Drepanocladus aduncus, Leptodictyum humile, and Sanionia uncinata clustered in one clade, which is sister to the Pylaisiaceae species Calliergonella cuspidata. The two Calliergonaceae species Calliergon sarmentosum and Warnstorfia exannulata form a clade and is sister to Amblystegiaceae and Pylaisiaceae.

Degradation of key photosynthetic genes in the critically endangered semi-aquatic flowering plant Saniculiphyllum guangxiense (Saxifragaceae)

BACKGROUND

Plastid gene loss and pseudogenization has been widely documented in parasitic and mycoheterotrophic plants, which have relaxed selective constraints on photosynthetic function. More enigmatic are sporadic reports of pseudogenization and loss of important photosynthesis genes in lineages thought to be fully photosynthetic. Here we report the complete plastid genome of Saniculiphyllum guangxiense, a critically endangered and phylogenetically isolated plant lineage, along with genomic evidence of reduced chloroplast function. We also report 22 additional plastid genomes representing the diversity of its containing clade Saxifragales, characterizing gene content and placing variation in a broader phylogenetic context.

RESULTS

We find that the plastid genome of Saniculiphyllum has experienced pseudogenization of five genes of the ndh complex (ndhA, ndhB, ndhD, ndhF, and ndhK), previously reported in flowering plants with an aquatic habit, as well as the surprising pseudogenization of two genes more central to photosynthesis (ccsA and cemA), contrasting with strong phylogenetic conservatism of plastid gene content in all other sampled Saxifragales. These genes participate in photooxidative protection, cytochrome synthesis, and carbon uptake. Nuclear paralogs exist for all seven plastid pseudogenes, yet these are also unlikely to be functional.

CONCLUSIONS

Saniculiphyllum appears to represent the greatest degree of plastid gene loss observed to date in any fully photosynthetic lineage, perhaps related to its extreme habitat specialization, yet plastid genome length, structure, and substitution rate are within the variation previously reported for photosynthetic plants. These results highlight the increasingly appreciated dynamism of plastid genomes, otherwise highly conserved across a billion years of green plant evolution, in plants with highly specialized life history traits.

Plastome of the mycoheterotrophic eudicot Exacum paucisquama (Gentianaceae) exhibits extensive gene loss and a highly expanded inverted repeat region

Mycoheterotrophic plants are highly specialized species able to acquire organic carbon from symbiotic fungi, with relaxed dependence on photosynthesis for carbon fixation. The relaxation of the functional constraint of photosynthesis and thereby the relaxed selective pressure on functional photosynthetic genes usually lead to substantial gene loss and a highly degraded plastid genome in heterotrophs. In this study, we sequenced and analyzed the plastome of the eudicot Exacum paucisquama, providing the first plastid genome of a mycoheterotroph in the family Gentianaceae to date. The E. paucisquama plastome was 44,028 bp in length, which is much smaller than the plastomes of autotrophic eudicots. Although the E. paucisquama plastome had a quadripartite structure, a distinct boundary shift was observed in comparison with the plastomes of other eudicots. We detected extensive gene loss and only 21 putative functional genes (15 protein-coding genes, four rRNA genes and two tRNA genes). Our results provide valuable information for comparative evolutionary analyses of plastomes of heterotrophic species belonging to different phylogenetic groups.

Complete plastome sequencing resolves taxonomic relationships among species of Calligonum L. (Polygonaceae) in China

BACKGROUND

Calligonum (Polygonaceae) is distributed from southern Europe through northern Africa to central Asia, and is typically found in arid, desert regions. Previous studies have revealed that standard DNA barcodes fail to discriminate Calligonum species. In this study, the complete plastid genomes (plastome) for 32 accessions of 21 Calligonum species is sequenced to not only generate the first complete plastome sequence for the genus Calligonum but to also 1) Assess the ability of the complete plastome sequence to discern species within the group, and 2) screen the plastome sequence for a cost-effective DNA barcode that can be used in future studies to resolve taxonomic relationships within the group.

RESULTS

The whole plastomes of Calligonum species possess a typical quadripartite structure. The size of the Calligonum plastome is approximately 161 kilobase pairs (kbp), and encodes 113 genes, including 79 protein-coding genes, 30 tRNA genes, and four rRNA genes. Based on ML phylogenetic tree analyses, the complete plastome has higher species identification (78%) than combinations of standard DNA barcodes (rbcL + matK + nrITS, 56%). Five newly screened gene regions (ndhF, trnS-G, trnC-petN, ndhF-rpl32, rpl32-trnL) had high species resolution, where ndhF and trnS-G were able to distinguish the highest proportion of Calligonum species (56%).

CONCLUSIONS

The entire plastid genome was the most effective barcode for the genus Calligonum, although other gene regions showed great potential as taxon-specific barcodes for species identification in Calligonum.

The loss of photosynthesis pathway and genomic locations of the lost plastid genes in a holoparasitic plant Aeginetia indica

BACKGROUND

With three origins of holoparasitism, Orobanchaceae provides an ideal system to study the evolution of holoparasitic lifestyle in plants. The evolution of holoparasitism can be revealed by plastid genome degradation and coordinated changes in the nuclear genome, since holoparasitic plants lost the capability of photosynthesis. Among the three clades with holoparasitic plants in Orobanchaceae, only Clade VI has no available plastid genome sequences for holoparasitic plants. In this study, we sequenced the plastome and transcriptome of Aeginetia indica, a holoparasitic plant in Clade VI of Orobanchaceae, to study its plastome evolution and the corresponding changes in the nuclear genome as a response of the loss of photosynthetic function.

RESULTS

The plastome of A. indica is reduced to 86,212 bp in size, and almost all photosynthesis-related genes were lost. Massive fragments of the lost plastid genes were transferred into the mitochondrial and/or nuclear genomes. These fragments could not be detected in its transcriptomes, suggesting that they were non-functional. Most protein coding genes in the plastome showed the signal of relaxation of purifying selection. Plastome and transcriptome analyses indicated that the photosynthesis pathway is completely lost, and that the porphyrin and chlorophyll metabolism pathway is partially retained, although chlorophyll synthesis is not possible.

CONCLUSIONS

Our study suggests the loss of photosynthesis-related functions in A. indica in both the nuclear and plastid genomes. The lost plastid genes are transferred into its nuclear and/or mitochondrial genomes, and exist in very small fragments with no expression and are thus non-functional. The Aeginetia indica plastome also provides a resource for comparative studies on the repeated evolution of holoparasitism in Orobanchaceae.

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.

-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.

Willmottiae (Paeoniaceae): characterization and phylogeny

The plastid genome (plastome) of the endemic Chinese medicinal herb Paeonia obovata subsp. Willmottiae (Paeoniaceae) was sequenced and investigated in this study. The complete plastome is 152,713 bp in length with the typical quadripartite structure, which consists of a large single-copy region (LSC, 84,419 bp), a small single-copy region (SSC, 16,982 bp), and a pair of inverted repeat regions (IRs, 25,656 bp). The overall GC content is 33.2%, and the IR regions are more GC rich (43.2%) than the LSC (36.7%) and SSC (32.8%) regions. A total of 114 unique genes, including 79 protein-coding genes, 31 tRNAs, and four rRNAs were identified. Phylogenetic reconstruction based on complete plastome sequences demonstrated that P. obovata subsp. Willmottiae is phylogenetically closest to P. obovata.

Large scale genome skimming from herbarium material for accurate plant identification and phylogenomics

BACKGROUND

Herbaria are valuable sources of extensive curated plant material that are now accessible to genetic studies because of advances in high-throughput, next-generation sequencing methods. As an applied assessment of large-scale recovery of plastid and ribosomal genome sequences from herbarium material for plant identification and phylogenomics, we sequenced 672 samples covering 21 families, 142 genera and 530 named and proposed named species. We explored the impact of parameters such as sample age, DNA concentration and quality, read depth and fragment length on plastid assembly error. We also tested the efficacy of DNA sequence information for identifying plant samples using 45 specimens recently collected in the Pilbara.

RESULTS

Genome skimming was effective at producing genomic information at large scale. Substantial sequence information on the chloroplast genome was obtained from 96.1% of samples, and complete or near-complete sequences of the nuclear ribosomal RNA gene repeat were obtained from 93.3% of samples. We were able to extract sequences for the core DNA barcode regions rbcL and matK from 96 to 93.3% of samples, respectively. Read quality and DNA fragment length had significant effects on sequencing outcomes and error correction of reads proved essential. Assembly problems were specific to certain taxa with low GC and high repeat content (Goodenia, Scaevola, Cyperus, Bulbostylis, Fimbristylis) suggesting biological rather than technical explanations. The structure of related genomes was needed to guide the assembly of repeats that exceeded the read length. DNA-based matching proved highly effective and showed that the efficacy for species identification declined in the order cpDNA >> rDNA > matK >> rbcL.

CONCLUSIONS

We showed that a large-scale approach to genome sequencing using herbarium specimens produces high-quality complete cpDNA and rDNA sequences as a source of data for DNA barcoding and phylogenomics.

Intra-individual heteroplasmy in the Gentiana tongolensis plastid genome (Gentianaceae)

Chloroplasts are typically inherited from the female parent and are haploid in most angiosperms, but rare intra-individual heteroplasmy in plastid genomes has been reported in plants. Here, we report an example of plastome heteroplasmy and its characteristics in Gentiana tongolensis (Gentianaceae). The plastid genome of G. tongolensis is 145,757 bp in size and is missing parts of petD gene when compared with other Gentiana species. A total of 112 single nucleotide polymorphisms (SNPs) and 31 indels with frequencies of more than 2% were detected in the plastid genome, and most were located in protein coding regions. Most sites with SNP frequencies of more than 10% were located in six genes in the LSC region. After verification via cloning and Sanger sequencing at three loci, heteroplasmy was identified in different individuals. The cause of heteroplasmy at the nucleotide level in plastome of G. tongolensis is unclear from the present data, although biparental plastid inheritance and transfer of plastid DNA seem to be most likely. This study implies that botanists should reconsider the heredity and evolution of chloroplasts and be cautious with using chloroplasts as genetic markers, especially in Gentiana.

The complete plastid genome of Iris domestica: a traditional Chinese medicine

Iris domestica has been used as Chinese traditional medicine to treat inflammation and throat disorders for many centuries. In this study, the complete plastid genome of I. domestica was first reported and characterized. The complete plastid genome is a typical quadripartite circular molecule of 153,729 bp in length, including a large single copy (LSC) region of 83,136 bp and a small single copy (SSC) region of 18,165 bp separated by two inverted repeat (IR) regions of 26,214 bp. A total of 132 genes including 86 protein-coding genes, 38 tRNA genes, and eight rRNA genes were identified. The phylogenetic analysis revealed that I. domestica was closer to I. gatesii.

Complete chloroplast genome of the tiny marine diatom Nanofrustulum shiloi (Bacillariophyta) from the Adriatic Sea

We report the chloroplast genome sequence of Nanofrustulum shiloi, a tiny araphid pennate diatom collected from the Adriatic Sea. The 160,994-bp N. shiloi genome displays a quadripartite structure and its gene repertoire resembles those of other diatom chloroplast genomes. Besides the genes located in the inverted repeat, psbY is duplicated. A gene-poor region in the large single-copy region contains multiple ORFs sharing sequence similarities with plasmids and chloroplast ORFs found in other diatom species. The genome features a single intron, a group II intron in petB. Phylogenomic analysis identified N. shiloi at a basal position within the araphid 2 clade.

Extensive plastome reduction and loss of photosynthesis genes in Diphelypaea coccinea, a holoparasitic plant of the family Orobanchaceae

BACKGROUND

Parasitic plants have the ability to obtain nutrients from their hosts and are less dependent on their own photosynthesis or completely lose this capacity. The reduction in plastid genome size and gene content in parasitic plants predominantly results from loss of photosynthetic genes. Plants from the family Orobanchaceae are used as models for studying plastid genome evolution in the transition from an autotrophic to parasitic lifestyle. Diphelypaea is a poorly studied genus of the Orobanchaceae, comprising two species of non-photosynthetic root holoparasites. In this study, we sequenced the plastid genome of Diphelypaea coccinea and compared it with other Orobanchaceae, to elucidate patterns of plastid genome evolution. In addition, we used plastid genome data to define the phylogenetic position of Diphelypaea spp.

METHODS

The complete nucleotide sequence of the plastid genome of D. coccinea was obtained from total plant DNA, using pyrosequencing technology.

RESULTS

The D. coccinea plastome is only 66,616 bp in length, and is highly rearranged; however, it retains a quadripartite structure. It contains only four rRNA genes, 25 tRNA genes and 25 protein-coding genes, being one of the most highly reduced plastomes among the parasitic Orobanchaceae. All genes related to photosynthesis, including the ATP synthase genes, had been lost, whereas most housekeeping genes remain intact. The plastome contains two divergent, but probably intact clpP genes. Intron loss had occurred in some protein-coding and tRNA genes. Phylogenetic analysis yielded a fully resolved tree for the Orobanchaceae, with Diphelypaea being a sister group to Orobanche sect. Orobanche.

Plastome of Quercus xanthoclada and comparison of genomic diversity amongst selected Quercus species using genome skimming

The genus Quercus L. contains several of the most economically important species for timber production in the Northern Hemisphere. It was one of the first genera described, but genetic diversity at a global scale within and amongst oak species remains unclear, despite numerous regional or species-specific assessments. To evaluate global plastid diversity in oaks, we sequenced the complete chloroplast of Quercus xanthoclada and compared its sequence with those available from other main taxonomic groups in Quercus. We quantify genomic divergence amongst oaks and performed a sliding window analysis to detect the most variable regions amongst members of the various clades, as well as divergent regions occurring in specific pairs of species. We identified private and shared SNPs amongst oaks species and sections and stress the need for a large global assessment of genetic diversity in this economically and ecologically important genus.