Insights into phylogeny, age and evolution of Allium (Amaryllidaceae) based on the whole plastome sequences

Incomplete lineage sorting and gene flow within Allium (Amayllidaceae)

The phylogeny and systematics of the genus Allium have been studied with a variety of diverse data types, including an increasing amount of molecular data. However, strong phylogenetic discordance and high levels of uncertainty have prevented the identification of a consistent phylogeny. The difficulty in establishing phylogenetic consensus and evidence for genealogical discordance make Allium a compelling test case to assess the relative contribution of incomplete lineage sorting (ILS), gene flow and gene tree estimation error on phylogenetic reconstruction. In this study, we obtained 75 transcriptomes of 38 Allium species across 10 subgenera. Whole plastid genome, single copy genes and consensus CDS were generated to estimate phylogenetic trees both using coalescence and concatenation methods. Multiple approaches including coalescence simulation, quartet sampling, reticulate network inference, sequence simulation, theta of ILS and reticulation index were carried out across the CDS gene trees to investigate the degrees of ILS, gene flow and gene tree estimation error. Afterward, a regression analysis was used to test the relative contributions of each of these forms of uncertainty to the final phylogeny. Despite extensive topological discordance among gene trees, we found a fully supported species tree that agrees with the most of well-accepted relationships and establishes monophyly of the genus Allium. We presented clear evidence for substantial ILS across the phylogeny of Allium. Further, we identified two ancient hybridization events for the formation of the second evolutionary line and subg. Butomissa as well as several introgression events between recently diverged species. Our regression analysis revealed that gene tree inference error and gene flow were the two most dominant factors explaining for the overall gene tree variation, with the difficulty in disentangling the effects of ILS and gene tree estimation error due to a positive correlation between them. Based on our efforts to mitigate the methodological errors in reconstructing trees, we believed ILS and gene flow are two principal reasons for the oft-reported phylogenetic heterogeneity of Allium. This study presents a strongly-supported and well-resolved phylogenetic backbone for the sampled Allium species, and exemplifies how to untangle heterogeneity in phylogenetic signal and reconstruct the true evolutionary history of the target taxa.

Identification of a candidate gene for the I locus determining the dominant white bulb color in onion (Allium cepa L.)

KEY MESSAGE

Through a map-based cloning approach, a gene coding for an R2R3-MYB transcription factor was identified as a causal gene for the I locus controlling the dominant white bulb color in onion. White bulb colors in onion (Allium cepa L.) are determined by either the C or I loci. The causal gene for the C locus was previously isolated, but the gene responsible for the I locus has not been identified yet. To identify candidate genes for the I locus, an approximately 7-Mb genomic DNA region harboring the I locus was obtained from onion and bunching onion (A. fistulosum) whole genome sequences using two tightly linked molecular markers. Within this interval, the AcMYB1 gene, known as a positive regulator of anthocyanin production, was identified. No polymorphic sequences were found between white and red AcMYB1 alleles in the 4,860-bp full-length genomic DNA sequences. However, a 4,838-bp LTR-retrotransposon was identified in the white allele, in the 79-bp upstream coding region from the stop codon. The insertion of this LTR-retrotransposon created a premature stop codon, resulting in the replacement of 26 amino acids with seven different residues. A molecular marker was developed based on the insertion of this LTR-retrotransposon to genotype the I locus. A perfect linkage between bulb color phenotypes and marker genotypes was observed among 5,303 individuals of segregating populations. The transcription of AcMYB1 appeared to be normal in both red and white onions, but the transcription of CHS-A, which encodes chalcone synthase and is involved in the first step of the anthocyanin biosynthesis pathway, was inactivated in the white onions. Taken together, an aberrant AcMYB1 protein produced from the mutant allele might be responsible for the dominant white bulb color in onions.

Comparative Analysis of Chloroplast Genome of Meconopsis (Papaveraceae) Provides Insights into Their Genomic Evolution and Adaptation to High Elevation

The Meconopsis species are widely distributed in the Qinghai-Tibet Plateau, Himalayas, and Hengduan Mountains in China, and have high medicinal and ornamental value. The high diversity of plant morphology in this genus poses significant challenges for species identification, given their propensity for highland dwelling, which makes it a question worth exploring how they cope with the harsh surroundings. In this study, we recently generated chloroplast (cp) genomes of two Meconopsis species, Meconopsis paniculata (M. paniculata) and M. pinnatifolia, and compared them with those of ten Meconopsis cp genomes to comprehend cp genomic features, their phylogenetic relationships, and what part they might play in plateau adaptation. These cp genomes shared a great deal of similarities in terms of genome size, structure, gene content, GC content, and codon usage patterns. The cp genomes were between 151,864 bp and 154,997 bp in length, and contain 133 predictive genes. Through sequence divergence analysis, we identified three highly variable regions (trnD-psbD, ccsA-ndhD, and ycf1 genes), which could be used as potential markers or DNA barcodes for phylogenetic analysis. Between 22 and 38 SSRs and some long repeat sequences were identified from 12 Meconopsis species. Our phylogenetic analysis confirmed that 12 species of Meconopsis clustered into a monophyletic clade in Papaveraceae, which corroborated their intrageneric relationships. The results indicated that M. pinnatifolia and M. paniculata are sister species in the phylogenetic tree. In addition, the atpA and ycf2 genes were positively selected in high-altitude species. The functions of these two genes might be involved in adaptation to the extreme environment in the cold and low CO2 concentration conditions at the plateau.

Structural divergence and phylogenetic relationships of Ajania (Asteraceae) from plastomes and ETS

BACKGROUND

Ajania Poljakov, an Asteraceae family member, grows mostly in Asia's arid and semi-desert areas and is a significant commercial and decorative plant. Nevertheless, the genus' classification has been disputed, and the evolutionary connections within the genus have not been thoroughly defined. Hence, we sequenced and analyzed Ajania's plastid genomes and combined them with ETS data to assess their phylogenetic relationships.

RESULTS

We obtained a total of six new Ajania plastid genomes and nine ETS sequences. The whole plastome lengths of the six species sampled ranged from 151,002 bp to 151,115 bp, showing conserved structures. Combined with publicly available data from GenBank, we constructed six datasets to reconstruct the phylogenetic relationships, detecting nucleoplasmic clashes. Our results reveal the affinities of Artemisia, Chrysanthemum and Stilpnolepis to Ajania and validate the early taxonomy reclassification. Some of the plastid genes with low phylogenetic information and gene trees with topological differences may have contributed to the ambiguous phylogenetic results of Ajania. There is extensive evolutionary rate heterogeneity in plastid genes. The psbH and ycf2 genes, which are involved in photosynthesis and ATP transport, are under selective pressure. Plastomes from Ajania species diverged, and structural aspects of plastomes may indicate some of the real evolutionary connections. We suggest the ycf1 gene as a viable plastid DNA barcode because it has significant nucleotide diversity and better reflects evolutionary connections.

CONCLUSION

Our findings validate the early Ajania taxonomy reclassification and show evolutionary rate heterogeneity, genetic variety, and phylogenetic heterogeneity of plastid genes. This research might provide new insights into the taxonomy and evolution of Ajania, as well as provide useful information for germplasm innovation and genetic enhancement in horticultural species.

Comparative and phylogenetic analysis of the complete chloroplast genomes of six Polygonatum species (Asparagaceae)

Polygonatum Miller belongs to the tribe Polygonateae of Asparagaceae. The horizontal creeping fleshy roots of several species in this genus serve as traditional Chinese medicine. Previous studies have mainly reported the size and gene contents of the plastomes, with little information on the comparative analysis of the plastid genomes of this genus. Additionally, there are still some species whose chloroplast genome information has not been reported. In this study, the complete plastomes of six Polygonatum were sequenced and assembled, among them, the chloroplast genome of P. campanulatum was reported for the first time. Comparative and phylogenetic analyses were then conducted with the published plastomes of three related species. Results indicated that the whole plastome length of the Polygonatum species ranged from 154,564 bp (P. multiflorum) to 156,028 bp (P. stenophyllum) having a quadripartite structure of LSC and SSC separated by two IR regions. A total of 113 unique genes were detected in each of the species. Comparative analysis revealed that gene content and total GC content in these species were highly identical. No significant contraction or expansion was observed in the IR boundaries among all the species except P. sibiricum1, in which the rps19 gene was pseudogenized owing to incomplete duplication. Abundant long dispersed repeats and SSRs were detected in each genome. There were five remarkably variable regions and 14 positively selected genes were identified among Polygonatum and Heteropolygonatum. Phylogenetic results based on chloroplast genome strongly supported the placement of P. campanulatum with alternate leaves in sect. Verticillata, a group characterized by whorled leaves. Moreover, P. verticillatum and P. cyrtonema were displayed as paraphyletic. This study revealed that the characters of plastomes in Polygonatum and Heteropolygonatum maintained a high degree of similarity. Five highly variable regions were found to be potential specific DNA barcodes in Polygonatum. Phylogenetic results suggested that leaf arrangement was not suitable as a basis for delimitation of subgeneric groups in Polygonatum and the definitions of P. cyrtonema and P. verticillatum require further study.

Plastid Phylogenomic Analyses Reveal a Cryptic Species of Ligusticopsis (Apiaceae, Angiosperms)

Ligusticopsis litangensis is identified and described as a cryptic species from Sichuan Province, China. Although the distribution of this cryptic species overlaps with that of Ligusticopsis capillacea and Ligusticopsis dielsiana, the morphological boundaries between them are explicit and have obviously distinguishable characters. The main distinguishing features of the cryptic species are as follows: long conical multi-branched roots, very short pedicels in compound umbels, unequal rays, oblong-globose fruits, 1-2 vittae per furrow and 3-4 vittae on the commissure. The above-mentioned features differ somewhat from other species within the genus Ligusticopsis, but generally coincide with the morphological boundaries defined for the genus Ligusticopsis. To determine the taxonomic position of L. litangensis, we sequenced and assembled the plastomes of L. litangensis and compared them with the plastomes of 11 other species of the genus Ligusticopsis. Notably, both phylogenetic analyses based on ITS sequences and the complete chloroplast genome robustly supported that three accessions of L. litangensis are monophyletic clade and then nested in Ligusticopsis genus. Moreover, the plastid genomes of 12 Ligusticopsis species, including the new species, were highly conserved in terms of gene order, gene content, codon bias, IR boundaries and SSR content. Overall, the integration of morphological, comparative genomic and phylogenetic evidence indicates that Ligusticopsis litangensis actually represents a new species.

New insights into the phylogenetic relationships among wild onions (Allium, Amaryllidaceae), with special emphasis on the subgenera Anguinum and Rhizirideum, as revealed by plastomes

The genus Allium, with over 900 species, is one of the largest monocotyledonous genera and is widely accepted with 15 recognized subgenera and 72 sections. The robust subgeneric and sectional relationships within Allium have long been not resolved. Based on 76 species of Allium (a total of 84 accessions), we developed a highly resolved plastome phylogenetic framework by integrating 18 newly sequenced species (20 accessions) in this study and assessed their subgeneric and sectional relationships, with special emphasis on the two subgenera Anguinum and Rhizirideum. We retrieved the three major evolutionary lines within Allium and found that the two subgenera Anguinum and Rhizirideum are monophyletic whereas others are highly polyphyletic (e.g., Allium, Cepa, Polyprason, and Melanocrommyum). Within the subgenus Anguinum, two strongly supported sublineages in East Asian and Eurasian-American were found. Allium tricoccum in North America belonged to the Eurasian clade. The distinct taxonomic status of A. ulleungense and its sister taxon were further determined. In subg. Rhizirideum, the Ulleung Island endemic A. dumebuchum shared its most recent common ancestor with the species from Mongolia and the narrow Korean endemic A. minus. Two Ulleung Island endemics were estimated to originate independently during the Pleistocene. In addition, a separate monotypic sectional treatment of the east Asian A. macrostemon (subg. Allium) and sister relationship between A. condensatum and A. chinense was suggested.

Plastome-based backbone phylogeny of East Asian Phedimus (Subgenus Aizoon: Crassulaceae), with special emphasis on Korean endemics

Although the monophyly of Phedimus has been strongly demonstrated, the species relationships among approximately 20 species of Phedimus have been difficult to determine because of the uniformity of their floral characteristics and extreme variation of their vegetative characters, often accompanied by high polyploid and aneuploid series and diverse habitats. In this study, we assembled 15 complete chloroplast genomes of Phedimus species from East Asia and generated a plastome-based backbone phylogeny of the subgenus Aizoon. As a proxy for nuclear phylogeny, we reconstructed the nuclear ribosomal DNA internal transcribed spacer (nrDNA ITS) phylogeny independently. The 15 plastomes of subg. Aizoon were highly conserved in structure and organization; hence, the complete plastome phylogeny fully resolved the species relationships with strong support. We found that P. aizoon and P. kamtschaticus were polyphyletic and morphologically distinct or ambiguous species, and they most likely evolved from the two species complex. The crown age of subg. Aizoon was estimated to be 27 Ma, suggesting its origin to be in the late Oligocene; however, the major lineages were diversified during the Miocene. The two Korean endemics, P. takesimensis and P. zokuriensis, were inferred to have originated recently during the Pleistocene, whereas the other endemic, P. latiovalifolium, originated in the late Miocene. Several mutation hotspots and seven positively selected chloroplast genes were identified in the subg. Aizoon.

Gradual genome size evolution and polyploidy in Allium from the Qinghai-Tibetan Plateau

BACKGROUND AND AIMS

Genome size is an important plant trait, with substantial interspecies variation. The mechanisms and selective pressures underlying genome size evolution are important topics in evolutionary biology. There is considerable diversity in Allium from the Qinghai-Tibetan Plateau, where genome size variation and related evolutionary mechanisms are poorly understood.

METHODS

We reconstructed the Allium phylogeny using DNA sequences from 71 species. We also estimated genome sizes of 62 species, and determined chromosome numbers in 65 species. We examined the phylogenetic signal associated with genome size variation, and tested how well the data fit different evolutionary models. Correlations between genome size variations and seed mass, altitude and 19 bioclimatic factors were determined.

KEY RESULTS

Allium genome sizes differed substantially between species and within diploids, triploids, tetraploids, hexaploids and octaploids. Size per monoploid genome (1Cx) tended to decrease with increasing ploidy levels. Allium polyploids tended to grow at a higher altitude than diploids. The phylogenetic tree was divided into three evolutionary branches. The genomes in Clade I were mostly close to the ancestral genome (18.781 pg) while those in Clades II and III tended to expand and contract, respectively. A weak phylogenetic signal was detected for Allium genome size. Furthermore, significant positive correlations were detected between genome size and seed mass, as well as between genome size and altitude. However, genome size was not correlated with 19 bioclimatic variables.

CONCLUSIONS

Allium genome size shows gradual evolution, followed by subsequent adaptive radiation. The three well-supported Allium clades are consistent with previous studies. The evolutionary patterns in different Allium clades revealed genome contraction, expansion and relative stasis. The Allium species in Clade II may follow adaptive radiation. The genome contraction in Clade III may be due to DNA loss after polyploidization. Allium genome size might be influenced by selective pressure due to the conditions on the Qinghai-Tibetan Plateau (low temperature, high UV irradiation and abundant phosphate in the soil).

Phylogeny and adaptive evolution of subgenus Rhizirideum (Amaryllidaceae, Allium) based on plastid genomes

The subgenus Rhizirideum in the genus Allium consists of 38 species worldwide and forms five sections (A. sect. Rhizomatosa, A. sect. Tenuissima, A. sect. Rhizirideum, A. sect. Eduardia, and A. sect. Caespitosoprason), A. sect. Caespitosoprason being merged into A. sect. Rhizomatosa recently. Previous studies on this subgenus mainly focused on separate sections. To investigate the inter-section and inter-subgenera phylogenetic relationships and adaptive evolution of A. subg. Rhizirideum, we selected thirteen representative species, which cover five sections of this subgenus and can represent four typical phenotypes of it. We conducted the comparative plastome analysis with our thirteen plastomes. And phylogenetic inferences with CDSs and complete sequences of plastomes of our thirteen species and another fifty-four related species were also performed. As a result, the A. subg. Rhizirideum plastomes were relatively conservative in structure, IR/SC borders, codon usage, and repeat sequence. In phylogenetic results, the inter-subgenera relationships among A. subg. Rhizirideum and other genus Allium subgenera were generally similar to the previous reports. In contrast, the inter-section relationships within our subgenus A. subg. Rhizirideum were newly resolved in this study. A. sect. Rhizomatosa and A. sect. Tenuissima were sister branches, which were then clustered with A. sect. Rhizirideum and A. sect. Eduardia successively. However, Allium Polyrhizum Turcz. ex Regel, type species of A. sect. Caespitosoprason, was resolved as the basal taxon of A. subg. Rhizirideum. Allium siphonanthum J. M. Xu was also found in clade A. subg. Cyathophora instead of clade A. subg. Rhizirideum. The selective pressure analysis was also conducted, and most protein-coding genes were under purifying selection. At the same time, just one gene, ycf2, was found under positive selection, and another three genes (rbcL, ycf1a, ycf1b) presented relaxed selection, which were all involved in the photosynthesis. The low temperature, dry climate, and high altitude of the extreme habitats where A. subg. Rhizirideum species grow might impose intense natural selection forces on their plastome genes for photosynthesis. In summary, our research provides new insights into the phylogeny and adaptive evolution of A. subg. Rhizirideum. Moreover, we suggest that the positions of the A. subg. Rhizirideum species A. polyrhizum and A. siphonanthum should be reconsidered.

The plastid genome of twenty-two species from Ferula, Talassia, and Soranthus: comparative analysis, phylogenetic implications, and adaptive evolution

BACKGROUND

The Ferula genus encompasses 180-185 species and is one of the largest genera in Apiaceae, with many of Ferula species possessing important medical value. The previous studies provided more information for Ferula, but its infrageneric relationships are still confusing. In addition, its genetic basis of its adaptive evolution remains poorly understood. Plastid genomes with more variable sites have the potential to reconstruct robust phylogeny in plants and investigate the adaptive evolution of plants. Although chloroplast genomes have been reported within the Ferula genus, few studies have been conducted using chloroplast genomes, especially for endemic species in China.

RESULTS

Comprehensively comparative analyses of 22 newly sequenced and assembled plastomes indicated that these plastomes had highly conserved genome structure, gene number, codon usage, and repeats type and distribution, but varied in plastomes size, GC content, and the SC/IR boundaries. Thirteen mutation hotspot regions were detected and they would serve as the promising DNA barcodes candidates for species identification in Ferula and related genera. Phylogenomic analyses with high supports and resolutions showed that Talassia transiliensis and Soranthus meyeri were nested in the Ferula genus, and thus they should be transferred into the Ferula genus. Our phylogenies also indicated the monophyly of subgenera Sinoferula and subgenera Narthex in Ferula genus. Twelve genes with significant posterior probabilities for codon sites were identified in the positively selective analysis, and their function may relate to the photosystem II, ATP subunit, and NADH dehydrogenase. Most of them might play an important role to help Ferula species adapt to high-temperatures, strong-light, and drought habitats.

CONCLUSION

Plastome data is powerful and efficient to improve the support and resolution of the complicated Ferula phylogeny. Twelve genes with significant posterior probabilities for codon sites were helpful for Ferula to adapt to the harsh environment. Overall, our study supplies a new perspective for comprehending the phylogeny and evolution of Ferula.

Plastome phylogenomics provide new perspective into the phylogeny and evolution of Betulaceae (Fagales)

BACKGROUND

Betulaceae is a relatively small but morphologically diverse family, with many species having important economic and ecological values. Although plastome structure of Betulaceae has been reported sporadically, a comprehensive exploration for plastome evolution is still lacking. Besides, previous phylogenies had been constructed based on limited gene fragments, generating unrobust phylogenetic framework and hindering further studies on divergence ages, biogeography and character evolution. Here, 109 plastomes (sixteen newly assembled and 93 previously published) were subject to comparative genomic and phylogenomic analyses to reconstruct a robust phylogeny and trace the diversification history of Betulaceae.

RESULTS

All Betulaceae plastomes were highly conserved in genome size, gene order, and structure, although specific variations such as gene loss and IR boundary shifts were revealed. Ten divergent hotspots, including five coding regions (P_i > 0.02) and five noncoding regions (P_i > 0.035), were identified as candidate DNA barcodes for phylogenetic analysis and species delimitation. Phylogenomic analyses yielded high-resolution topology that supported reciprocal monophyly between Betula and Alnus within Betuloideae, and successive divergence of Corylus, Ostryopsis, and Carpinus-Ostrya within Coryloideae. Incomplete lineage sorting and hybridization may be responsible for the mutual paraphyly between Ostrya and Carpinus. Betulaceae ancestors originated from East Asia during the upper Cretaceous; dispersals and subsequent vicariance accompanied by historical environment changes contributed to its diversification and intercontinental disjunction. Ancestral state reconstruction indicated the acquisition of many taxonomic characters was actually the results of parallel or reversal evolution.

CONCLUSIONS

Our research represents the most comprehensive taxon-sampled and plastome-level phylogenetic inference for Betulaceae to date. The results clearly document global patterns of plastome structural evolution, and established a well-supported phylogeny of Betulaceae. The robust phylogenetic framework not only provides new insights into the intergeneric relationships, but also contributes to a perspective on the diversification history and evolution of the family.

Comparative and phylogenetic analysis of the complete chloroplast genome sequences of Allium mongolicum

Allium mongolicum Regel is a wild and sandy vegetable with unique flavours. In this study, a complete chloroplast (cp) genome of A. mongolicum was obtained (Genbank accession number: OM630416), and contained 153,609 base pairs with the GC ratio as 36.8%. 130 genes were annotated including 84 protein-coding genes, 38 tRNA, and 8 rRNA genes. The large single-copy (LSC) region was 82,644 bp, and a small single-copy (SSC) region was 18,049 bp, which were separated by two inverted repeats (IRs, including IRa and IRb) of 26,458 bp. Comparative genome analyses of 55 Allium species suggested that genomic structure of genus Allium was conserved, and LSC and SSC regions were outstanding with high variability. Among them, more divergent loci were in the SSC region covering ycf1-rrn4.5 and ndhF-ccsA. Phylogenetic analysis on cp genomes of 55 Allium determined that all members were clustered into 13 clades, and A. mongolicum had close relationship with A. senescens. Corresponding analyses of four protein-coding genes (ycf1, ndhF, rpl32, and ccsA) in aforementioned divergent loci confirmed that ycf1 was finally chosen as the candidate gene for species identification and evolutionary classification of genus Allium. These data provide valuable genetic resources for future research on Allium.

Allium sulaimanicum: A new Allium species and section from Pakistan

A new species, Allium sulaimanicum, is described from northern Balochistan and southern Khyber Pakhtunkhwa in Pakistan based on morphological, molecular, and cytological studies. The new species is characterised by long runner-like cylindrical rhizomes of adult plants, cylindrical bulbs, linear leaves with minute soft hairs along veins, campanulate perigonium, and white to creamy white, ovate to elliptical, 4.5-5-mm-long acute tepals, with brownish to purplish nerves, stamens as long as to slightly longer than tepals, yellow to brick red anthers, hexagonal ovary, and white and papillate/warty along angles. The presence of long herbaceous rhizomes indicated serious isolation of the new species; hence, a new section Sulaimanicum is proposed to accommodate the new species. The new species is diploid with a chromosome number of 2n = 16. Detailed morphological description, illustrations, phylogenetic analyses based on sequences of plastid spacers (rpl32-trnL (UAG) and trnQ-rps16) and nuclear ITS, karyotype features, and a distribution map of the new species are provided.

The phylogeny of Seseli (Apiaceae, Apioideae): insights from molecular and morphological data

BACKGROUND

The genus Seseli L., which consists of 125-140 species distributed in the Old World from western Europe and northwestern Africa to China and Japan, is one of the largest and most taxonomically difficult genera of Apiaceae Lindl. Although several previous studies have been conducted on Seseli based on limited morphological characteristics and molecular fragments, a robust and comprehensive phylogeny of Seseli remains elusive. Plastomes provide abundant genetic information and have been widely used in studying plant phylogeny and evolution. Consequently, we newly generated the complete plastomes of eleven Seseli taxa. We combined plastome data and morphological characteristics to investigate the phylogeny of Seseli.

RESULTS

In our study, we observed that the genome length, gene numbers, IR/SC borders, and repeat composition of the eleven Seseli plastomes were variable. Several appropriate mutation hotspot regions may be developed as candidate DNA barcodes for evolution, phylogeny, and species identification of Seseli. The phylogenetic results identified that Seseli was not a monophyletic group. Moreover, the eleven newly sequenced Seseli taxa did not cluster with S. tortuosum (the type species of Seseli, belonging to the tribe Selineae), where S. delavayi clustered with Eriocycla belonging to the tribe Echinophoreae and the other ten belonged to Selineae. The comparative plastome and morphological characteristics analyses confirmed the reliability of the phylogenetic analyses and implied the complex evolution of Seseli.

CONCLUSION

Combining molecular and morphological data is efficient and useful for studying the phylogeny of Seseli. We suggest that "a narrow sense" of Seseli will be meaningful for further study and the current taxonomic system of Seseli needs to be revised. In summary, our study can provide new insights into the phylogenetic relationships and taxonomic framework of Seseli.

A Multi-Considered Seed Coat Pattern Classification of Allium L. Using Unsupervised Machine Learning

The seed coat sculpture is one of the most important taxonomic distinguishing features. The objective of this study is to classify coat patterns of Allium L. seeds into new groups using scanning electron microscopy unsupervised machine learning. Selected images of seed coat patterns from more than 100 Allium species described in literature and data from our samples were classified into seven types of anticlinal (irregular curved, irregular curved to nearly straight, straight, S, U, U to Ω, and Ω) and five types of periclinal walls (granule, small verrucae, large verrucae, marginal verrucae, and verrucate verrucae). We used five unsupervised machine learning approaches: K-means, K-means++, Minibatch K-means, Spectral, and Birch. The elbow and silhouette approaches were then used to determine the number of clusters required. Thereafter, we compared human- and machine-based results and proposed a new clustering. We then separated the data into six target clusters: SI, SS, SM, NS, PS, and PD. The proposed strongly identical grouping is distinct from the other groups in that the results are exactly the same, but PD is unrelated to the others. Thus, unsupervised machine learning has been shown to support the development of new groups in the Allium seed coat pattern.

Plastid phylogenomic insights into relationships, divergence, and evolution of Apiales

Members of Apiales are monophyletic and radiated in the Late Cretaceous. Fruit morphologies are critical for Apiales evolution and negative selection and mutation pressure play important roles in environmental adaptation. Apiales include many foods, spices, medicinal, and ornamental plants, but the phylogenetic relationships, origin and divergence, and adaptive evolution remain poorly understood. Here, we reconstructed Apiales phylogeny based on 72 plastid genes from 280 species plastid genomes representing six of seven families of this order. Highly supported phylogenetic relationships were detected, which revealed that each family of Apiales is monophyletic and confirmed that Pennanticeae is a member of Apiales. Genera Centella and Dickinsia are members of Apiaceae, and the genus Hydrocotyle previously classified into Apiaceae is confirmed to belong to Araliaceae. Besides, coalescent phylogenetic analysis and gene trees cluster revealed ten genes that can be used for distinguishing species among families of Apiales. Molecular dating suggested that the Apiales originated during the mid-Cretaceous (109.51 Ma), with the families' radiation occurring in the Late Cretaceous. Apiaceae species exhibit higher differentiation compared to other families. Ancestral trait reconstruction suggested that fruit morphological evolution may be related to shifts in plant types (herbaceous or woody), which in turn is related to the distribution areas and species numbers. Codon bias and positive selection analyses suggest that negative selection and mutation pressure may play important roles in environmental adaptation of Apiales members. Our results improve the phylogenetic framework of Apiales and provide insights into the origin, divergence, and adaptive evolution of this order and its members.

Complete chloroplast genomes and comparative analyses of Hippeastrum ‘milady’, Hippeastrum albertii and Hippeastrum reticulatum (Amaryllidaceae)

Hippeastrum is a genus of ornamental plants with large, brightly colored flowers. Due to the very high seed-setting rate of the hybridization of Hippeastrum, the large population of hybrid progeny and the existence of superparent inheritance, it is difficult to trace the origin of the varieties collected from the market during breeding. In this study, we analyzed the chloroplast genomes of Hippeastrum ‘Milady’, H. alberti, and H. reticulatum using the Illumina NovaSeq sequencing platform and generated full-length sequences of 158,067, 158,067, and 158,522 bp, respectively. All three genomes had the typical tetrad structure. The large single copy, small single copy, and inverted repeat regions of H. reticulatum were observed to be respectively 277, 138, and 20 bp longer than the corresponding regions of H. ‘Milady’ and H. alberti. The results of comparative analysis of simple sequence repeats (SSRs), Ka/Ks ratios, codon preferences, and complete sequences of chloroplasts of these three taxa and 14 other plant species were as follows. First, the chloroplast genomes of H. ‘Milady’, H. alberti, and H. reticulatum contain 209, 209, and 211 SSR sites, respectively, most of which (123, 123, and 122, respectively) are single nucleotide repeats. Second, leucine, arginine, and serine are the most frequently used amino acids in the three chloroplast genomes. Third, H. ‘Milady’, H. alberti, and H. reticulatum are more closely related to Lycoris and Narcissus than to Allium and Agapanthus. Our results will provide information on the study of origins or relatedness of native species, and the identification of cultivars.

Comparative Analysis of the Complete Chloroplast Genomes in Allium Section Bromatorrhiza Species (Amaryllidaceae): Phylogenetic Relationship and Adaptive Evolution

With the development of molecular sequencing approaches, many taxonomic and phylogenetic problems of the genus Allium L. have been solved; however, the phylogenetic relationships of some subgenera or sections, such as section Bromatorrhiza, remain unresolved, which has greatly impeded our full understanding of the species relationships among the major clades of Allium. In this study, the complete chloroplast (cp) genomes of nine species in the Allium sect. Bromatorrhiza were determined using the Illumina paired-end sequencing, the NOVOPlasty de novo assembly strategy, and the PGA annotation method. The results showed that the cp genome exhibited high conservation and revealed a typical circular tetrad structure. Among the sect. Bromatorrhiza species, the gene content, SSRs, codon usage, and RNA editing site were similar. The genome structure and IR regions’ fluctuation were investigated while genes, CDSs, and non-coding regions were extracted for phylogeny reconstruction. Evolutionary rates (Ka/Ks values) were calculated, and positive selection analysis was further performed using the branch-site model. Five hypervariable regions were identified as candidate molecular markers for species authentication. A clear relationship among the sect. Bromatorrhiza species were detected based on concatenated genes and CDSs, respectively, which suggested that sect. Bromatorrhiza is monophyly. In addition, there were three genes with higher Ka/Ks values (rps2, ycf1, and ycf2), and four genes (rpoC2, atpF, atpI, and rpl14) were further revealed to own positive selected sites. These results provide new insights into the plastome component, phylogeny, and evolution of Allium species.

Seed macro- and micromorphology in Allium (Amaryllidaceae) and its phylogenetic significance

BACKGROUND AND AIMS

Macro- and micromorphology of seeds are diagnostic characteristics of importance in delimiting taxa in Allium (Amaryllidaceae). However, there is no consensus on the phylogenetic significance of testa cell characteristics and whether they reflect the different evolutionary levels recognized in Allium.

METHODS

Seeds of 95 species (98 samples) representing 14 subgenera and 58 sections of Allium were examined using scanning electron microscopy (SEM) for such traits as periclinal wall surface area of ten testa cells, distance between testa cells (macromorphology), testa cell shapes, and arrangement and structure of anticlinal and periclinal walls (micromorphology). The data matrix was subjected to cladistic analysis. The produced phylogenetic tree was examined against the molecular tree obtained from publically available ITS sequences.

KEY RESULTS

The periclinal wall surface area of ten testa cells and the distance between them, examined for the first time, were found useful for delimitation of species in Allium. Based on seed macro- and micromorphology, we present a taxonomic key and a hypothetical reconstruction of the migration routes during the early stages of evolution of Allium.

CONCLUSIONS

The ancestors of Allium originated in an area bounded by the Caucasus, Central Asia and Iran. The seed testa morphology-based evolutionary state of a species is determined by two parameters: the shape of the periclinal walls and curvature of the anticlinal walls.

Biosynthesis and Metabolism of Garlic Odor Compounds in Cultivated Chinese Chives (Allium tuberosum) and Wild Chinese Chives (Allium hookeri)

Chinese chives is a popular herb vegetable and medicine in Asian countries. Southwest China is one of the centers of origin, and the mountainous areas in this region are rich in wild germplasm. In this study, we collected four samples of germplasm from different altitudes: a land race of cultivated Chinese chives (Allium tuberosum), wide-leaf chives and extra-wide-leaf chives (Allium hookeri), and ovoid-leaf chives (Allium funckiaefolium). Leaf metabolites were detected and compared between A. tuberosum and A. hookeri. A total of 158 differentially accumulated metabolites (DAM) were identified by Gas Chromatography—Mass Spectrometry (GC-MS) and Liquid Chromatography—Mass Spectrometry (LC-MS), among which there was a wide range of garlic odor compounds, free amino acids, and sugars. A. hookeri contains a higher content of fructose, garlic odor compounds, and amino acids than A. tuberosum, which is supported by the higher expression level of biosynthetic genes revealed by transcriptome analysis. A. hookeri accumulates the same garlic odor compound precursors that A. tuberosum does (mainly methiin and alliin). We isolated full-length gene sequences of phytochelatin synthase (PCS), γ-glutamyltranspeptidases (GGT), flavin-containing monooxygenase (FMO), and alliinase (ALN). These sequences showed closer relations in phylogenetic analysis between A. hookeri and A. tuberosum (with sequence identities ranging from 86% to 90%) than with Allium cepa or Allium sativum (which had a lower sequence identity ranging from 76% to 88%). Among these assayed genes, ALN, the critical gene controlling the conversion of odorless precursors into odor compounds, was undetected in leaves, bulbs, and roots of A. tuberosum, which could account for its weaker garlic smell. Moreover, we identified a distinct FMO1 gene in extra-wide-leaf A. hookeri that is due to a CDS-deletion and frameshift mutation. These results above reveal the molecular and metabolomic basis of impressive strong odor in wild Chinese chives.

Allium pallasii and A. caricifolium—Surprisingly Diverse Old Steppe Species, Showing a Clear Geographical Barrier in the Area of Lake Zaysan

Polymorph Allium pallasii s.l. from monotypic A. sect. Pallasia was studied using a wide spectrum of methods and divided into two clearly morphologically, geographically, cytologically and genetically isolated species: A. pallasii s. str.—North-East Kazakhstan, Western Siberia, and the Altai Mountains; A. caricifolium—Kyrgyzstan, Northwest China, South-East Kazakhstan until Zaysan Lake in the east. Despite serious genetic differences, both species are sisters and are related to species of the A. sect. Codonoprasum (Subg. Allium). Allium caricifolium differs from A. pallasii s. str. by taller stems, dense inflorescence, and with filaments longer than perianth. The possible phylogenetic reasons for the separation of these species are discussed. A nomenclature analysis of synonyms was carried out.

Comparative Plastome Analysis of Three Amaryllidaceae Subfamilies: Insights into Variation of Genome Characteristics, Phylogeny, and Adaptive Evolution

In the latest APG IV classification system, Amaryllidaceae is placed under the order of Asparagus and includes three subfamilies: Agapanthoideae, Allioideae, and Amaryllidoideae, which include many economically important crops. With the development of molecular phylogeny, research on the phylogenetic relationship of Amaryllidaceae has become more convenient. However, the current comparative analysis of Amaryllidaceae at the whole chloroplast genome level is still lacking. In this study, we sequenced 18 Allioideae plastomes and combined them with publicly available data (a total of 41 plastomes), including 21 Allioideae species, 1 Agapanthoideae species, 14 Amaryllidoideae species, and 5 Asparagaceae species. Comparative analyses were performed including basic characteristics of genome structure, codon usage, repeat elements, IR boundary, and genome divergence. Phylogenetic relationships were detected using single-copy genes (SCGs) and ribosomal internal transcribed spacer sequences (ITS), and the branch-site model was also employed to conduct the positive selection analysis. The results indicated that all Amaryllidaceae species showed a highly conserved typical tetrad structure. The GC content and five codon usage indexes in Allioideae species were lower than those in the other two subfamilies. Comparison analysis of Bayesian and ML phylogeny based on SCGs strongly supports the monophyly of three subfamilies and the sisterhood among them. Besides, positively selected genes (PSGs) were detected in each of the three subfamilies. Almost all genes with significant posterior probabilities for codon sites were associated with self-replication and photosynthesis. Our study investigated the three subfamilies of Amaryllidaceae at the whole chloroplast genome level and suggested the key role of selective pressure in the adaptation and evolution of Amaryllidaceae.

Alliumheterophyllum (Amaryllidaceae), a new species from Henan, China

Alliumheterophyllum D.F.Xie & X.J.He, sp. nov. (Amaryllidaceae), is a new species from Henan, China and is described based on morphological and molecular evidence. It is morphologically most similar to A.dumebuchum in the rhomboid scape in cross-section. However, distinctive differences were detected in perianth color, leaf shape and cross-section, flowers' density as well as flowering season. Similarly, the karyotype of A.heterophyllum is 2n = 2x = 16 and in A.dumebuchum is 2n = 4x = 32. Phylogenetic analysis based on nuclear ribosomal Internal Transcribed Spacers (ITS) and three cpDNA regions strongly supports that A.heterophyllum is a member of Allium section Rhizirideum and sister to the other species of this section (e.g. A.senescens, A.spirale, and A.prostratum). Currently, only one population and approximately 120 individuals were discovered; the development of scenic spots in this region may affect its growth and threaten this population. Therefore, this new species is preliminarily considered as Near Threatened (NT) according to criteria of the IUCN Red List.

Phylogeny, Age, and Evolution of Tribe Lilieae (Liliaceae) Based on Whole Plastid Genomes

Tribe Lilieae, encompassing Lilium, Notholirion, Cardiocrinum, and Fritillaria, includes economically important crops with a horticultural and medicinal value. It is considered to be a core lineage of Liliaceae, but phylogenetic relationships within it, and the timing of the origin of individual clades, remain incompletely resolved. To address these issues, we reconstructed the evolutionary history of the tribe. We sequenced 45 Liliaceae plastomes and combined them with publicly available data (for a total of 139 plastomes) to explore the systematics, origin, divergence, and evolution of Lilieae. Our taxon sampling covers all ten sections of Lilium, all Cardiocrinum species, three Notholirion species, and major phylogenetic clades of Fritillaria. Our phylogenetic analysis confirms the monophyly of major sections/subgenera of Lilium and Fritillaria with strong support. We dated the origin of Lilieae to the Eocene, with genera and species radiations inferred to have occurred in the Miocene. The reconstruction of the ancestral area implies that Lilieae may have originated from the Qinghai-Tibet Plateau (QTP): the Himalayas and Hengduan Mountains and uplifting of the QTP likely promoted divergence within the tribe. Ancestral-state reconstructions of the bulb component number (including bulblets and scales) show a strong correlation with the genus-level phylogenetic diversity in Lilieae. They also predict that the most recent common ancestor of Lilieae had bulbs with numerous bulblets. Based on these observations, we predicted that climatic oscillations associated with the QTP uplift played an important role in the evolution of the Lilieae bulb. Our findings provide a well-supported picture of evolutionary relationships and a useful framework for understanding the pathway of bulb evolution within Lilieae, contributing to a better understanding of the evolutionary history of lilies.

Comparative genomics and phylogenetic relationships of two endemic and endangered species (Handeliodendron bodinieri and Eurycorymbus cavaleriei) of two monotypic genera within Sapindales

BACKGROUND

Handeliodendron Rehder and Eurycorymbus Hand.-Mazz. are the monotypic genera in the Sapindaceae family. The phylogenetic relationship of these endangered species Handeliodendron bodinieri (Lévl.) Rehd. and Eurycorymbus cavaleriei (Lévl.) Rehd. et Hand.-Mazz. with other members of Sapindaceae s.l. is not well resolved. A previous study concluded that the genus Aesculus might be paraphyletic because Handeliodendron was nested within it based on small DNA fragments. Thus, their chloroplast genomic information and comparative genomic analysis with other Sapindaceae species are necessary and crucial to understand the circumscription and plastome evolution of this family.

RESULTS

The chloroplast genome sizes of Handeliodendron bodinieri and Eurycorymbus cavaleriei are 151,271 and 158,690 bp, respectively. Results showed that a total of 114 unique genes were annotated in H. bodinieri and E. cavaleriei, and the ycf1 gene contained abundant SSRs in both genomes. Comparative analysis revealed that gene content, PCGs, and total GC content were remarkably similar or identical within 13 genera from Sapindaceae, and the chloroplast genome size of four genera was generally smaller within the family, including Acer, Dipteronia, Aesculus, and Handeliodendron. IR boundaries of the H. bodinieri showed a significant contraction, whereas it presented a notable expansion in E. cavaleriei cp genome. Ycf1, ndhC-trnV-UAC, and rpl32-trnL-UAG-ccsA were remarkably divergent regions in the Sapindaceae species. Analysis of selection pressure showed that there are a few positively selected genes. Phylogenetic analysis based on different datasets, including whole chloroplast genome sequences, coding sequences, large single-copy, small single-copy, and inverted repeat regions, consistently demonstrated that H. bodinieri was sister to the clade consisting of Aesculus chinensis and A. wangii and strongly support Eurycorymbus cavaleriei as sister to Dodonaea viscosa.

CONCLUSION

This study revealed that the cp genome size of the Hippocastanoideae was generally smaller compared to the other subfamilies within Sapindaceae, and three highly divergent regions could be used as the specific DNA barcodes within Sapindaceae. Phylogenetic results strongly support that the subdivision of four subfamilies within Sapindaceae, and Handeliodendron is not nested within the genus Aesculus.

High-Throughput Genomic Data Reveal Complex Phylogenetic Relationships in Stylosanthes Sw (Leguminosae)

Allopolyploidy is widely present across plant lineages. Though estimating the correct phylogenetic relationships and origin of allopolyploids may sometimes become a hard task. In the genus Stylosanthes Sw. (Leguminosae), an important legume crop, allopolyploidy is a key speciation force. This makes difficult adequate species recognition and breeding efforts on the genus. Based on comparative analysis of nine high-throughput sequencing (HTS) samples, including three allopolyploids (S. capitata Vogel cv. “Campo Grande,” S. capitata “RS024” and S. scabra Vogel) and six diploids (S. hamata Taub, S. viscosa (L.) Sw., S. macrocephala M. B. Ferreira and Sousa Costa, S. guianensis (Aubl.) Sw., S. pilosa M. B. Ferreira and Sousa Costa and S. seabrana B. L. Maass & 't Mannetje) we provide a working pipeline to identify organelle and nuclear genome signatures that allowed us to trace the origin and parental genome recognition of allopolyploids. First, organelle genomes were de novo assembled and used to identify maternal genome donors by alignment-based phylogenies and synteny analysis. Second, nuclear-derived reads were subjected to repetitive DNA identification with RepeatExplorer2. Identified repeats were compared based on abundance and presence on diploids in relation to allopolyploids by comparative repeat analysis. Third, reads were extracted and grouped based on the following groups: chloroplast, mitochondrial, satellite DNA, ribosomal DNA, repeat clustered- and total genomic reads. These sets of reads were then subjected to alignment and assembly free phylogenetic analyses and were compared to classical alignment-based phylogenetic methods. Comparative analysis of shared and unique satellite repeats also allowed the tracing of allopolyploid origin in Stylosanthes, especially those with high abundance such as the StyloSat1 in the Scabra complex. This satellite was in situ mapped in the proximal region of the chromosomes and made it possible to identify its previously proposed parents. Hence, with simple genome skimming data we were able to provide evidence for the recognition of parental genomes and understand genome evolution of two Stylosanthes allopolyploids.

Centromere size scales with genome size across Eukaryotes

Previous studies on grass species suggested that the total centromere size (sum of all centromere sizes in a cell) may be determined by the genome size, possibly because stable scaling is important for proper cell division. However, it is unclear whether this relationship is universal. Here we analyze the total centromere size using the CenH3-immunofluorescence area as a proxy in 130 taxa including plants, animals, fungi, and protists. We verified the reliability of our methodological approach by comparing our measurements with available ChIP-seq-based measurements of the size of CenH3-binding domains. Data based on these two independent methods showed the same positive relationship between the total centromere size and genome size. Our results demonstrate that the genome size is a strong predictor (R-squared = 0.964) of the total centromere size universally across Eukaryotes. We also show that this relationship is independent of phylogenetic relatedness and centromere type (monocentric, metapolycentric, and holocentric), implying a common mechanism maintaining stable total centromere size in Eukaryotes.

Comparative Chloroplast Genomes of Four Lycoris Species (Amaryllidaceae) Provides New Insight into Interspecific Relationship and Phylogeny

The genus Lycoris (Amaryllidaceae) consists of about 20 species, which is endemic to East Asia. Although the Lycoris species is of great horticultural and medical importance, challenges in accurate species identification persist due to frequent natural hybridization and large-scale intraspecific variation. In this study, we sequenced chloroplast genomes of four Lycoris species and retrieved seven published chloroplast (cp) genome sequences in this genus for comparative genomic and phylogenetic analyses. The cp genomes of these four newly sequenced species were found to be 158,405-158,498 bp with the same GC content of 37.8%. The structure of the genomes exhibited the typical quadripartite structure with conserved gene order and content. A total of 113 genes (20 duplicated) were identified, including 79 protein-coding genes (PCGs), 30 tRNAs, and 4 rRNAs. Phylogenetic analysis showed that the 11 species were clustered into three main groups, and L. sprengeri locate at the base of Lycoriss. The L. radiata was suggested to be the female donor of the L. incarnata, L. shaanxiensis, and L. squamigera. The L. straminea and L. houdyshelii may be derived from L. anhuiensis, L. chinensis, or L. longituba. These results could not only offer a genome-scale platform for identification and utilization of Lycoris but also provide a phylogenomic framework for future studies in this genus.

Gene Loss, Pseudogenization in Plastomes of Genus Allium (Amaryllidaceae), and Putative Selection for Adaptation to Environmental Conditions

Amaryllidaceae is a large family with more than 1,600 species, belonging to 75 genera. The largest genus—Allium—is vast, comprising about a thousand species. Allium species (as well as other members of the Amaryllidaceae) are widespread and diversified, they are adapted to a wide range of habitats from shady forests to open habitats like meadows, steppes, and deserts. The genes present in chloroplast genomes (plastomes) play fundamental roles for the photosynthetic plants. Plastome traits could thus be associated with geophysical abiotic characteristics of habitats. Most chloroplast genes are highly conserved and are used as phylogenetic markers for many families of vascular plants. Nevertheless, some studies revealed signatures of positive selection in chloroplast genes of many plant families including Amaryllidaceae. We have sequenced plastomes of the following nine Allium (tribe Allieae of Allioideae) species: A. zebdanense, A. moly, A. victorialis, A. macleanii, A. nutans, A. obliquum, A. schoenoprasum, A. pskemense, A. platyspathum, A. fistulosum, A. semenovii, and Nothoscordum bivalve (tribe Leucocoryneae of Allioideae). We compared our data with previously published plastomes and provided our interpretation of Allium plastome genes’ annotations because we found some noteworthy inconsistencies with annotations previously reported. For Allium species we estimated the integral evolutionary rate, counted SNPs and indels per nucleotide position as well as compared pseudogenization events in species of three main phylogenetic lines of genus Allium to estimate whether they are potentially important for plant physiology or just follow the phylogenetic pattern. During examination of the 38 species of Allium and the 11 of other Amaryllidaceae species we found that rps16, rps2, infA, ccsA genes have lost their functionality multiple times in different species (regularly evolutionary events), while the pseudogenization of other genes was stochastic events. We found that the “normal” or “pseudo” state of rps16, rps2, infA, ccsA genes correlates well with the evolutionary line of genus the species belongs to. The positive selection in various NADH dehydrogenase (ndh) genes as well as in matK, accD, and some others were found. Taking into account known mechanisms of coping with excessive light by cyclic electron transport, we can hypothesize that adaptive evolution in genes, coding subunits of NADH-plastoquinone oxidoreductase could be driven by abiotic factors of alpine habitats, especially by intensive light and UV radiation.

Phylogenetics and comparative plastome genomics of two of the largest genera of angiosperms, Piper and Peperomia (Piperaceae)

Biological radiations provide unique opportunities to understand the evolution of biodiversity. One such radiation is the pepper plant family Piperaceae, an early-diverging and mega-diverse lineage that could serve as a model to study the diversification of angiosperms. However, traditional genetic markers lack sufficient variation for such studies, and testing hypotheses on poorly resolved phylogenetic frameworks becomes challenging. Limited genomic data is available for Piperaceae, which contains two of the largest genera of angiosperms, Piper (>2100 species) and Peperomia (>1300 species). To address this gap, we used genome skimming to assemble and annotate whole plastomes (152-161kbp) and >5kbp nuclear ribosomal DNA region from representatives of Piper and Peperomia. We conducted phylogenetic and comparative genomic analyses to study plastome evolution and investigate the role of hybridization in this group. Plastome phylogenetic trees were well resolved and highly supported, with a hard incongruence observed between plastome and nuclear phylogenetic trees suggesting hybridization in Piper. While all plastomes of Piper and Peperomia had the same gene content and order, there were informative structural differences between them. First, ycf1 was more variable and longer in Piper than Peperomia, extending well into the small single copy region by thousands of base pairs. We also discovered previously unknown structural variation in 14 out of 25 Piper taxa, tandem duplication of the trnH-GUG gene resulting in an expanded large single copy region. Other early-diverging angiosperms have a duplicated trnH-GUG, but the specific rearrangement we found is unique to Piper and serves to refine knowledge of relationships among early-diverging angiosperms. Our study demonstrates that genome skimming is an efficient approach to produce plastome assemblies for comparative genomics and robust phylogenies of species-rich plant genera.

Out of the Qinghai-Tibetan Plateau and rapid radiation across Eurasia for Allium section Daghestanica (Amaryllidaceae)

The disjunctive distribution (Europe-Caucasus-Asia) and species diversification across Eurasia for the genus Allium sect. Daghestanica has fascinating attractions for researchers aiming to understanding the development and history of modern Eurasia flora. However, no any studies have been carried out to address the evolutionary history of this section. Based on the nrITS and cpDNA fragments (trnL-trnF and rpl32-trnL), the evolutionary history of the third evolutionary line (EL3) of the genus Allium was reconstructed and we further elucidated the evolutionary line of sect. Daghestanica under this background. Our molecular phylogeny recovered two highly supported clades in sect. Daghestanica: the Clade I includes Caucasian-European species and Asian A. maowenense, A. xinlongense and A. carolinianum collected in Qinghai; the Clade II comprises Asian yellowish tepal species, A. chrysanthum, A. chrysocephalum, A. herderianum, A. rude and A. xichuanense. The divergence time estimation and biogeography inference indicated that Asian ancestor located in the Qinghai-Tibetan Plateau (QTP) and the adjacent region could have migrated to Caucasus and Europe distributions around the Late Miocene and resulted in further divergence and speciation; Asian ancestor underwent the rapid radiation in the QTP and the adjacent region most likely due to the heterogeneous ecology of the QTP resulted from the orogeneses around 4-3 million years ago (Mya). Our study provides a picture to understand the origin and species diversification across Eurasia for sect. Daghestanica.

Backbone phylogeny and evolution of Apioideae (Apiaceae): New insights from phylogenomic analyses of plastome data

Traditional phylogenies inferred from chloroplast DNA fragments have not obtained a well-resolved evolutionary history for the backbone of Apioideae, the largest subfamily of Apiaceae. In this study, we applied the genome skimming approach of next-generation sequencing to address whether the lack of resolution at the tip of the Apioideae phylogenetic tree is due to limited information loci or the footprint of ancient radiation. A total of 90 complete chloroplast genomes (including 23 newly sequenced genomes and covering 20 major clades of Apioideae) were analyzed (RAxML and MrBayes) to provide a phylogenomic reconstruction of Apioideae. Dating analysis was also implemented using BEAST to estimate the origin and divergence time of the major clades. As a result, the early divergences of Apioideae have been clarified but the relationship among its distally branching clades (Group A) was only partially resolved, with short internal branches pointing to an ancient radiation scenario. Four major clades, Tordyliinae I, Pimpinelleae I, Apieae and Coriandreae, were hypothesized to have originated from chloroplast capture events induced by early hybridization according to the incongruence between chloroplast-based and nrDNA-based phylogenetic trees. Furthermore, the variable and nested distribution of junction positions of LSC (Large single copy region) and IR_B (inverted repeat region B) in Group A may reflect incomplete lineage sorting within this group, which possibly contributed to the unclear phylogenetic relationships among these clades inferred from plastome data. Molecular clock analysis revealed the chloroplast capture events mainly occurred during the middle to late Miocene, providing a geological and climate context for the evolution of Apioideae.

Complete chloroplast genomes shed light on phylogenetic relationships, divergence time, and biogeography of Allioideae (Amaryllidaceae)

Allioideae includes economically important bulb crops such as garlic, onion, leeks, and some ornamental plants in Amaryllidaceae. Here, we reported the complete chloroplast genome (cpDNA) sequences of 17 species of Allioideae, five of Amaryllidoideae, and one of Agapanthoideae. These cpDNA sequences represent 80 protein-coding, 30 tRNA, and four rRNA genes, and range from 151,808 to 159,998 bp in length. Loss and pseudogenization of multiple genes (i.e., rps2, infA, and rpl22) appear to have occurred multiple times during the evolution of Alloideae. Additionally, eight mutation hotspots, including rps15-ycf1, rps16-trnQ-UUG, petG-trnW-CCA, psbA upstream, rpl32-trnL-UAG, ycf1, rpl22, matK, and ndhF, were identified in the studied Allium species. Additionally, we present the first phylogenomic analysis among the four tribes of Allioideae based on 74 cpDNA coding regions of 21 species of Allioideae, five species of Amaryllidoideae, one species of Agapanthoideae, and five species representing selected members of Asparagales. Our molecular phylogenomic results strongly support the monophyly of Allioideae, which is sister to Amaryllioideae. Within Allioideae, Tulbaghieae was sister to Gilliesieae-Leucocoryneae whereas Allieae was sister to the clade of Tulbaghieae- Gilliesieae-Leucocoryneae. Molecular dating analyses revealed the crown age of Allioideae in the Eocene (40.1 mya) followed by differentiation of Allieae in the early Miocene (21.3 mya). The split of Gilliesieae from Leucocoryneae was estimated at 16.5 mya. Biogeographic reconstruction suggests an African origin for Allioideae and subsequent spread to Eurasia during the middle Eocene. Cool and arid conditions during the late Eocene led to isolation between African and Eurasian species. African Allioideae may have diverged to South American taxa in the late Oligocene. Rather than vicariance, long-distance dispersal is the most likely explanation for intercontinental distribution of African and South American Allioideae species.

Plastomes of eight Ligusticum species: characterization, genome evolution, and phylogenetic relationships

BACKGROUND

The genus Ligusticum consists of approximately 60 species distributed in the Northern Hemisphere. It is one of the most taxonomically difficult taxa within Apiaceae, largely due to the varied morphological characteristics. To investigate the plastome evolution and phylogenetic relationships of Ligusticum, we determined the complete plastome sequences of eight Ligusticum species using a de novo assembly approach.

RESULTS

Through a comprehensive comparative analysis, we found that the eight plastomes were similar in terms of repeat sequence, SSR, codon usage, and RNA editing site. However, compared with the other seven species, L. delavayi exhibited striking differences in genome size, gene number, IR/SC borders, and sequence identity. Most of the genes remained under the purifying selection, whereas four genes showed relaxed selection, namely ccsA, rpoA, ycf1, and ycf2. Non-monophyly of Ligusticum species was inferred from the plastomes and internal transcribed spacer (ITS) sequences phylogenetic analyses.

CONCLUSION

The plastome tree and ITS tree produced incongruent tree topologies, which may be attributed to the hybridization and incomplete lineage sorting. Our study highlighted the advantage of plastome with mass informative sites in resolving phylogenetic relationships. Moreover, combined with the previous studies, we considered that the current taxonomy system of Ligusticum needs to be improved and revised. In summary, our study provides new insights into the plastome evolution, phylogeny, and taxonomy of Ligusticum species.

Complete Chloroplast Genomes and Comparative Analyses of L. chinensis, L. anhuiensis, and L. aurea (Amaryllidaceae)

The genus Lycoris (about 20 species) includes important medicinal and ornamental plants. Due to the similar morphological features and insufficient genomic resources, germplasm identification and molecular phylogeny analysis are very limited. Here, we sequenced the complete chloroplast genomes of L. chinensis, L. anhuiensis, and L. aurea; they have very similar morphological traits that make it difficult to identify. The full length of their cp genomes was nearly 158k bp with the same guanine-cytosine content of 37.8%. A total of 137 genes were annotated, including 87 protein-coding genes, 42 tRNAs, and eight rRNAs. A comparative analysis revealed the conservation in sequence size, GC content, and gene content. Some variations were observed in repeat structures, gene expansion on the IR-SC (Inverted Repeat-Single-Copy) boundary regions. Together with the cpSSR (chloroplast simple sequence repeats), these genetic variations are useful to develop molecular markers for germplasm identification. Phylogenetic analysis showed that seven Lycoris species were clustered into a monophyletic group, and closed to Narcissus in Amaryllidaceae. L. chinensis, L. anhuiensis, and L. longituba were clustered together, suggesting that they were very likely to be derived from one species, and had the same ancestor with L. squamigera. Our results provided information on the study of genetic diversity, origins or relatedness of native species, and the identification of cultivars.