Plastid phylogenomic insights into relationships of all flowering plant families

Phylogenomic and morphological evidence supports the reinstatement of the bamboo genus Clavinodum from Oligostachyum (Poaceae: Bambusoideae)

One of the most intractable problems in bamboo systematics concerns the three-branched bamboos of tribe Arundinarieae (Poaceae: Bambusoideae), which are collectively characterized by having three branches per mid-culm node. Previous phylogenetic studies based on double-digest restriction-site associated DNA sequencing (ddRAD-seq) data confirmed that Oligostachyum, a member of this group, is non-monophyletic, and in particular that Oligostachyum oedogonatum is a problematic species deserving further attention, as it appears to be morphologically and phylogenetically distinct from the other three-branched bamboos. Here we aim to define and confirm the phylogenetic position of O. oedogonatum, by including representatives from across its geographic range. We also provide new insights into the overall phylogeny of the three-branched bamboos and closely related genera, using multiple phylogenomic datasets. While a plastid genome-based tree is very poorly supported, phylogenies inferred using two sets of conserved nuclear genes and single nucleotide polymorphism (SNP) data yield generally well-supported and congruent topologies using coalescent-based approaches. The tree inferred from the largest concatenated gene set is the most dissimilar to other inferences. The nuclear-based data sets all recover a major clade that includes all of the three-branched bamboos and four other genera, which can be distinguished from related taxa due to their possession of three stigmas per floret and leptomorph rhizomes. Notably, eight O. oedogonatum samples form a clade that is distantly related to other members of Oligostachyum, including the type species of the genus (Oligostachyum sulcatum). Population genetic approaches and multi-species coalescent-based analysis of the nuclear data sets imply that seven of these populations can be treated as a single species, O. oedogonatum, but that one population from Jinggangshan is likely an intergeneric hybrid between O. oedogonatum and Pleioblastus. Morphologically, O. oedogonatum differs from all other three-branched bamboos, in having strongly asymmetrically swollen supra-nodal ridges, a laterally compressed spikelet, and rachilla segments that disarticulate readily below fertile florets. Because of its morphological distinctiveness and molecular phylogenetic position, we propose that this taxon should be reinstated as Clavinodum oedogonatum. We provide a new description for this monotypic genus here.

Phylogenomic conflict analyses of plastid and mitochondrial genomes of Impatiens (Balsaminaceae) reveal its complex evolutionary history

Impatiens is among the most diverse angiosperm genera, comprising more than 1000 species. The phylogenetic relationship among sections of Impatiens remains unclear. Plastomes and mitogenomes are useful for resolving problematic relationships in plant phylogenetics; however, conflicts between the organellar genomes have been reported. Here, we reconstructed the phylogeny of Impatiens using concatenated and multispecies coalescent (MSC) methods based on coding and noncoding regions of the plastome and coding regions of the mitogenome from 139 species, representing all major clades in Impatiens. Conflict analyses were conducted to test and visualize the incongruences between the organellar genomes and within the plastome. The analyses supported the monophyly of all subgenera and sections and identified a new clade (clade Longlinensis), but the relationships among these sections are inconsistent. There was incongruence between the organellar genome trees regarding the relationships among sect. Semeiocardium, sect. Racemosae and clade Longlinensis. There was also incongruence within the plastome regarding the relationships among sections Fasciculatae, Impatiens, Tuberosae, Scorpioidae, and Uniflorae. Our results show that incongruence between organellar genomes likely results from the complex evolutionary history of the genus, involving mixed inheritance of organellar genomes and hybridization. The incongruence within the plastome may result from the limited phylogenetic signal in plastome data, which could be due to the rapid radiation between 15.07 and 12.93 Ma. Specific genes and regions that led to such incongruence have been identified. By confirming the monophyly of Impatiens sections and detecting phylogenetic conflicts, this study provides a unique plastid and mitogenomic perspective on Impatiens phylogeny.

Phylogenomic Inference Suggests Differential Deep Time Phylogenetic Signals from Nuclear and Organellar Genomes in Gymnosperms

The living gymnosperms include about 1200 species in five major groups: cycads, ginkgo, gnetophytes, Pinaceae (conifers I), and cupressophytes (conifers II). Molecular phylogenetic studies have yet to reach a unanimously agreed-upon relationship among them. Moreover, cytonuclear phylogenetic incongruence has been repeatedly observed in gymnosperms. We collated a comprehensive dataset from available genomes of 17 gymnosperms across the five major groups and added our own high-quality assembly of a species from Podocarpaceae (the second largest conifer family) to increase sampling width. We used these data to infer reconciled nuclear species phylogenies using two separate methods to ensure the robustness of our conclusions. We also reconstructed organelle phylogenomic trees from 42 mitochondrial and 82 plastid genes from 38 and 289 gymnosperm species across the five major groups, respectively. Our nuclear phylogeny consistently recovers the Ginkgo-cycads clade as the first lineage split from other gymnosperm clades and the Pinaceae as sister to gnetophytes (the Gnepines hypothesis). In contrast, the mitochondrial tree places cycads as the earliest lineage in gymnosperms and gnetophytes as sister to cupressophytes (the Gnecup hypothesis) while the plastomic tree supports the Ginkgo-cycads clade and gnetophytes as the sister to cupressophytes. We also examined the effect of mitochondrial RNA editing sites on the gymnosperm phylogeny by manipulating the nucleotide and amino acid sequences at these sites. Only complete removal of editing sites has an effect on phylogenetic inference, leading to a closer congruence between mitogenomic and nuclear phylogenies. This suggests that RNA editing sites carry a phylogenetic signal with distinct evolutionary traits.

Plastid-nuclear coevolution of ribosomal protein genes in papilionoid legumes

In plants, cellular function is orchestrated by three distinct genomes located within the nucleus, mitochondrion, and plastid. These genomes are interdependent, requiring tightly coordinated maintenance and expression. Plastids host several multisubunit protein complexes encoded by both the plastid and nuclear genomes. To investigate plastid-nuclear coevolution, this study focused on plastid ribosomal protein genes that are encoded by both plastid and nuclear genomes from 50 taxa across 15 of the 22 early branching major clades of the legume subfamily Papilionoideae. Comparative analysis of substitution rates was conducted across five gene sets: nuclear-encoded plastid-targeted ribosomal protein genes (NuCpRP), nuclear-encoded cytosol-targeted ribosomal genes (NuCyRP), other nuclear-encoded plastid-targeted genes that are not involved in ribosomes (NuCpOT), plastid-encoded ribosomal protein genes (CpRP) and plastid-encoded photosynthesis genes (CpPS).1 Elevated nonsynonymous substitution rates (dN) and ratios of nonsynonymous to synonymous substitution rates (dN/dS; ω) were observed in both CpRP and NuCpRP compared to the other gene sets. Significant differences in dN for CpRP and NuCpRP were found between the papilionoid 50-kb inversion clade and other legumes. Using coevolution statistics and evolutionary rate covariation, strong signals of cytonuclear coevolution were identified, where nonsynonymous substitutions in CpRP and NuCpRP genes co-occur along the same branches of the Papilionoideae phylogeny. Increased ω in a few CpRP genes was due to intensified positive selection whereas most of the CpRP and NuCpRP increased ω was caused by relaxed purifying selection. This pattern not only underscores the role of cytonuclear incompatibility in driving speciation but also highlights its constraints on the genetic enhancement of papilionoid crop species.

A 24-nt miR9560 modulates the transporter gene BrpHMA2 expression in Brassica parachinensis

MicroRNAs (miRNAs) control gene expression in plant through transcript cleavage and translation inhibition. Recently, 24-nt miRNAs have been shown to direct DNA methylation at target sites, regulating the neighboring gene expression. Our study focused on miR9560, a 24-nt miRNA induced by cadmium (Cd) stress in Brassica rapa ssp. parachinensis (B. parachinensis). Phylogenetic analysis revealed miR9560 predominantly emerged in the Rosanae superorder and was conserved in Brassicaceae, with potential target sites adjacent to transporter family genes HMAs. RNA gel blotting showed that mature miR9560 was only detected in various Brassica crops roots after Cd stress. In B. parachinensis, miR9560's putative target site is upstream of BrpHMA2, an afflux-type Cd transporter. In a transient expression system of B. parachinensis protoplasts, the expression of miR9560 increased the DNA methylation upstream of BrpHMA2, reducing the transcription of BrpHMA2. This regulation was also observed in Arabidopsis wild-type protoplasts but not in the mutants dcl234 and ago4 with impairments in the RNA-dependent DNA methylation (RdDM) pathway. We deduced that miR9560 modulates BrpHMA2 expression via the RdDM pathway, potentially regulating Cd uptake and movement in B. parachinensis. Furthermore, this regulatory mechanism may extend to other Brassica plants. This study enhances our comprehension of 24-nt miRNAs role in regulating Cd accumulation within Brassica plants.

Extensive cytonuclear discordance revealed by phylogenomic analyses suggests complex evolutionary history in the holly genus Ilex (Aquifoliaceae)

Ilex L., the exclusive genus of Aquifoliaceae, encompasses over 600 dioecious wood species with a highly irregular distribution, predominantly found in South America and Asia. The phylogeny and classification of this genus remain enigmatic due to significant early extinctions, constrained morphological diversity, recent hybridization/introgression, and conflicting signals from previously utilized markers. This study presents phylogenetic reconstructions based on complete chloroplast genome sequences and single nucleotide polymorphisms (SNPs) derived from genome resequencing data. A total of 116 accessions of Ilex, representing approximately 108 taxa, were included as the ingroup, with five accessions of two species serving as outgroups. Analysis of the chloroplast genome and nuclear SNP data individually resulted in two robust phylogenetic trees, revealing substantial discrepancies between the chloroplast genome and nuclear SNP phylogenies at both the species and clade levels. The chloroplast genome sequences successfully resolved relationships within this genus into eight strongly supported major clades, while the nuclear SNPs resolved relationships into seven highly supported major clades. Our nuclear SNP phylogenetic tree, in comparison to the chloroplast genome tree, aligns more closely with the recently updated classification of Ilex in multiple instances. The extensive cytonuclear discordance identified may be attributed to recent hybridization events and incomplete lineage sorting (ILS).

Phylogenomics of angiosperms based on mitochondrial genes: insights into deep node relationships

BACKGROUND

Angiosperms are the largest plant group and play an essential role in the biosphere. Phylogenetic relationships of many families and orders remain contentious, and, in an attempt to address these, we performed the most extensive sampling of mitochondrial genes to date.

RESULTS

We reconstructed a seed plant phylogenetic framework based on 41 mitochondrial protein-coding sequences (mtCDSs), representing 335 families and 63 orders with 481 angiosperm species. The results for major clades of angiosperms produced moderate to strong support (> 70% bootstrap) for more than 80% of nodes and strong support for most orders. Eight major nodes were supported, including the three paraphyletic ANA orders (Amborellales, Nymphaeales, and Austrobaileyales) and five major core-angiosperm clades. Chloranthales and Ceratophyllales are sister to the eudicots, whereas the monocots are sister to the magnoliids. Although well-supported, relationships within the asterids and rosids were in some cases unresolved or weakly supported, due to the low levels of variability detected in these genes.

CONCLUSIONS

Our results indicated that mitochondrial genomic data were effective at resolving deep node relationships of angiosperm phylogeny and thus represent an important resource for phylogenetics and evolutionary studies of angiosperm.

Two complete chloroplast genomes of Ceratophyllum, an aquatic genus with unresolved phylogenetic position

Ceratophyllum is an aquatic genus noted for its enigmatic position in the angiosperm phylogenetic tree. In this study, we assembled and annotated the chloroplast genomes of two species. The chloroplast genome length of Ceratophyllum platyacanthum subsp. oryzetorum (Kom.) (V.Komarov, 1988) and Ceratophyllum submersum L. (Carl Linnaeus, 1763) is 156,168 bp and 156,554 bp, respectively. The chloroplast genomes of Ceratophyllum encode 113 unique genes, including 79 protein-coding genes, four rRNA genes, and 30 tRNA genes. The assembly of these two chloroplast genomes not only contributes to our understanding of the genome of Ceratophyllum but also provides valuable insights for the evolutionary study of angiosperms.

Comparative analysis of the complete chloroplast genome of seven Wikstroemia taxa (Thymelaeaceae) provides insights into the genome structure and phylogenetic relationships

MAIN CONCLUSION

New insights into the phylogeny of species in the family Thymelaeaceae and support of the recognition of D. genkwa and D. aurantiaca as species in the genus Wikstroemia are provided. Wikstroemia (Thymelaeaceae) is an economically important genus because some of its species are used in traditional medicine and also contribute to pulp production. The morphological characteristics of Wikstroemia species exhibit continuous natural variation, posing a challenge in accurately distinguishing this genus from its sister genera solely based on morphological traits. Consequently, the classification of, and phylogenetic relationships between, Wikstroemia and its sister genera, as inferred from morphological characteristics, remain contentious. Chloroplast genome information has proven to be a valuable tool in plant phylogeny. Here, we performed a comparative analysis of the chloroplast genomes of 15 species in the genus Wikstroemia, all of which exhibited typical quadripartite structures, with sizes ranging from 150,054 bp to 175,898bp. These genomes encoded 122-143 genes, including 79-95 protein-coding genes, 36-40 tRNA genes, and 8 rRNA genes. The overall GC content displayed minimal variation, ranging from 36.6% to 37.47%. The distributions of SSRs and codon bias exhibited similarities among Wikstroemia species. High variability hotspots were found in 15 intergenic spacers and 5 genes. Phylogenetic analyses consistently grouped all Wikstroemia species into a single clade. Notably, Daphne genkwa and D. aurantiaca were found to be nested within Wikstroemia, rather than being closely related to other Daphne species. Furthermore, phylogenetic analyses suggested that Wikstroemia is paraphyletic relative to Stellera chamaejasme. These findings provide new insights into the phylogeny of Wikstroemia and Daphne within the Thymelaeaceae, contributing to improved species identification and increasing the taxonomic and phylogenetic resolution of Wikstroemia.

Modeling compositional heterogeneity resolves deep phylogeny of flowering plants

Angiosperms experienced one of the most remarkable radiations of land plants and are now the dominant autotrophs in terrestrial ecosystems. Recent phylogenomic studies based on large-scale data from plastid, mitochondrial, or nuclear transcriptomes/genomes and increased taxon sampling have provided unprecedent resolution into the phylogeny of flowering plants. However, owing to ancient rapid radiations, the interrelationships among the five lineages of Mesangiospermae, the vast majority of angiosperms, remain contentious. Here we show that, although plastid and mitochondrial genomes lack sufficient phylogenetic signal for resolving deeper phylogeny, the relationships among five mesangiosperm lineages can be confidently resolved under better-fitting models using genome-scale data. According to our Bayesian cross-validation and model test in a maximum likelihood framework, site-heterogeneous models (e.g., CAT-GTR + G4, LG + C20 + F + G) outperform site-homogeneous or partition models often used in previous studies. Under site-heterogeneous models, the approximately unbiased test favored our preferred tree recovered from various datasets: Ceratophyllales (coontails) are robustly recovered as sister to monocots, and they together are sister to the clade comprising magnoliids, Chloranthales, and eudicots. Our phylogenomic analyses resolve the last enigma of the deeper phylogeny of angiosperms and emphasize the efficacy of modeling compositional heterogeneity in resolving rapid radiations of plants.

Toward a phylogenomic classification of magnoliids

PREMISE

Magnoliids are a strongly supported clade of angiosperms. Previous phylogenetic studies based primarily on analyses of a limited number of mostly plastid markers have led to the current classification of magnoliids into four orders and 18 families. However, uncertainty remains regarding the placement of several families.

METHODS

For the first comprehensive phylogenomic analysis of magnoliids as a whole, we sampled 235 species from 199 (74%) genera and representing all families and most subfamilies and tribes. We analyzed newly generated data from the Angiosperms353 probe set using both coalescent and concatenation analyses and testing the impact of multiple filtering and alignment strategies.

RESULTS

While our results generally provide further support for previously established phylogenetic relationships in both magnoliids as a whole and large families including Annonaceae and Lauraceae, they also provide new evidence for previously ambiguous relationships. In particular, we found support for the position of Hydnoraceae as sister to the remainder of Piperales, though evidence was conflicting, and resolved the backbone of relationships among most genera of Myristicaceae. Different analytical strategies tended to have rather small effects on branch support and topology.

CONCLUSIONS

Although some of our results are limited by low gene recovery for a number of taxa and significant gene tree conflict for some relationships, this study represents a significant step toward reconstructing the evolutionary history of a major lineage of angiosperms. Based on these results, we present an updated phylogenetic classification for magnoliids, recognizing 21 families, summarizing previously established subfamilies and tribes, and describing new tribes for Myristicaceae.

Photosynthetic demands on translational machinery drive retention of redundant tRNA metabolism in plant organelles

Eukaryotic nuclear genomes often encode distinct sets of translation machinery for function in the cytosol vs. organelles (mitochondria and plastids). This raises questions about why multiple translation systems are maintained even though they are capable of comparable functions and whether they evolve differently depending on the compartment where they operate. These questions are particularly interesting in plants because translation machinery, including aminoacyl-transfer RNA (tRNA) synthetases (aaRS), is often dual-targeted to the plastids and mitochondria. These organelles have different functions, with much higher rates of translation in plastids to supply the abundant, rapid-turnover proteins required for photosynthesis. Previous studies have indicated that plant organellar aaRS evolve more slowly compared to mitochondrial aaRS in eukaryotes that lack plastids. Thus, we investigated the evolution of nuclear-encoded organellar and cytosolic aaRS and tRNA maturation enzymes across a broad sampling of angiosperms, including nonphotosynthetic (heterotrophic) plant species with reduced plastid gene expression, to test the hypothesis that translational demands associated with photosynthesis constrain the evolution of enzymes involved in organellar tRNA metabolism. Remarkably, heterotrophic plants exhibited wholesale loss of many organelle-targeted aaRS and other enzymes, even though translation still occurs in their mitochondria and plastids. These losses were often accompanied by apparent retargeting of cytosolic enzymes and tRNAs to the organelles, sometimes preserving aaRS-tRNA charging relationships but other times creating surprising mismatches between cytosolic aaRS and mitochondrial tRNA substrates. Our findings indicate that the presence of a photosynthetic plastid drives the retention of specialized systems for organellar tRNA metabolism.

De Novo Sequencing of Drymaria villosa and Comparative Analysis of Plastome in Caryophyllaceae Across 23 Species

Plant plastome are well studied due to their essential roles in photosynthesis and plant development. Comparative studies among plastome of closely related genera or families are limited, hindering our understanding of evolutionary changes and adaptation. This study presents a comparative analysis of 23 Caryophyllaceae plastome revealing a dynamic interplay of conserved and variable features. The genome size exhibited a moderate coefficient of variation (CV) of 2.58%. The large single-copy (LSC) and small single-copy (SSC) regions were highly conserved, with CVs of 2.55% and 2.00%, respectively. In contrast, the inverted repeat (IR) regions displayed greater variability, with a CV of 4.23%, indicating dynamic evolutionary processes. Exon counts varied significantly (CV 17.20%), while intron counts showed some variability (CV 7.79%), reflecting diverse gene structures. Coding sequences had moderate variability (CV 3.67%), while non-coding sequences varied more (CV 5.05%). tRNA counts were slightly variable (CV 2.67%), and GC content was notably consistent (CV 0.40%). This study includes the newly sequenced plastome of Drymaria villosa (GenBank accession OR790517), confirming its placement within Caryophyllaceae with significant diversification through phylogenetic analysis. Correlations (> 0.6) among plastome components and genome size reflect their tight evolutionary linkage, enhancing our understanding of plastome evolution in Caryophyllaceae and aiding future investigations into the ecological and medicinal potential of D. villosa and related species.

Comparative case study of evolutionary insights and floral complexity in key early-diverging eudicot Ranunculales models

Famously referred to as "Darwin's abominable mystery," the rapid diversification of angiosperms over the last ~140 million years presents a fascinating enigma. This diversification is underpinned by complex genetic pathways that evolve and rewire to produce diverse and sometimes novel floral forms. Morphological innovations in flowers are shaped not only by genetics but also by evolutionary constraints and ecological dynamics. The importance of model organisms in addressing the long-standing scientific questions related to diverse floral forms cannot be overstated. In plant biology, Arabidopsis thaliana, a core eudicot, has emerged as a premier model system, with its genome being the first plant genome to be fully sequenced. Similarly, model systems derived from crop plants such as Oryza sativa (rice) and Zea mays (maize) have been invaluable, particularly for crop improvement. However, despite their substantial utility, these model systems have limitations, especially when it comes to exploring the evolution of diverse and novel floral forms. The order Ranunculales is the earliest-diverging lineage of eudicots, situated phylogenetically between core eudicots and monocots. This group is characterized by its exceptional floral diversity, showcasing a wide range of floral morphologies and adaptations that offer valuable insights into the evolutionary processes of flowering plants. Over the past two decades, the development of at least five model systems including, Aquilegia, Thalictrum, Nigella, Delphinium and Eschscholzia within the Ranunculales order has significantly advanced our understanding of floral evolution. This review highlights the conservation and divergence of floral organ identity programs observed among these models and discusses their importance in advancing research within the field. The review also delves into elaborate petal morphology observed in Aquilegia, Nigella, and Delphinium genera, and further discusses the contributions, limitations, and future research directions for Ranunculales model systems. Integrating these diverse models from the early-diverging eudicot order has enhanced our understanding of the complex evolutionary pathways that shape floral diversity in angiosperms, bridging the knowledge gaps essential for a comprehensive understanding of floral evolution.

The adaptive evolution of Quercus section Ilex using the chloroplast genomes of two threatened species

Chloroplast (cp) genome sequences have been extensively used for phylogenetic and evolutionary analyses, as many have been sequenced in recent years. Identification of Quercus is challenging because many species overlap phenotypically owing to interspecific hybridization, introgression, and incomplete lineage sorting. Therefore, we wanted to gain a better understanding of this genus at the level of the maternally inherited chloroplast genome. Here, we sequenced, assembled, and annotated the cp genomes of the threatened Quercus marlipoensis (160,995 bp) and Q. kingiana (161,167 bp), and mined these genomes for repeat sequences and codon usage bias. Comparative genomic analyses, phylogenomics, and selection pressure analysis were also performed in these two threatened species along with other species of Quercus. We found that the guanine and cytosine content of the two cp genomes were similar. All 131 annotated genes, including 86 protein-coding genes, 37 transfer RNA genes, and 8 ribosomal RNA genes, had the same order in the two species. A strong A/T bias was detected in the base composition of simple sequence repeats. Among the 59 synonymous codons, the codon usage pattern of the cp genomes in these two species was more inclined toward the A/U ending. Comparative genomic analyses indicated that the cp genomes of Quercus section Ilex are highly conserved. We detected eight highly variable regions that could be used as molecular markers for species identification. The cp genome structure was consistent and different within and among the sections of Quercus. The phylogenetic analysis showed that section Ilex was not monophyletic and was divided into two groups, which were respectively nested with section Cerris and section Cyclobalanopsis. The two threatened species sequenced in this study were grouped into the section Cyclobalanopsis. In conclusion, the analyses of cp genomes of Q. marlipoensis and Q. kingiana promote further study of the taxonomy, phylogeny and evolution of these two threatened species and Quercus.

The chromosome-level genome assembly of Cananga odorata provides insights into its evolution and terpenoid biosynthesis

Cananga odorata is known as a natural perfume tree of the Annonaceae family in Magnoliales. However, its phylogenetic position and the molecular mechanisms involved in the biosynthesis of the floral volatile organic compounds (VOCs) remain unclear. Here, by combining a variety of sequencing platforms, we present a telomere-to-telomere (T2T) genome of C. odorata with 735.83 Mb, which represents the highest integrity and assembly quality of genome in magnoliid plants reported to date. Phylogenetic analysis based on multiple datasets and approaches showed that C. odorata, as a member of magnoliids, is sister to eudicots, after their divergence from monocots. Metabolomic of VOCs in the essential oil and flowers scent showed that sesquiterpenes, especially β-caryophyllene, were the major compounds. Two CoTPS21 homologues derived from tandem duplication events were highly expressed during flower development and were identified as the key sesquiterpene synthases for the production of β-caryophyllene. In addition, CoSPL3 and CoSPL9 were considered as potential transcription factors for activating the expression of CoTPS21 homologues. Our results shed light on the molecular mechanisms underlying the biosynthesis of the unique floral fragrance in C. odorata and provide new insights into the phylogenetic position of magnoliids.

Comparative analysis of 12 water lily plastid genomes reveals genomic divergence and evolutionary relationships in early flowering plants

The aquatic plant Nymphaea, a model genus of the early flowering plant lineage Nymphaeales and family Nymphaeaceae, has been extensively studied. However, the availability of chloroplast genome data for this genus is incomplete, and phylogenetic relationships within the order Nymphaeales remain controversial. In this study, 12 chloroplast genomes of Nymphaea were assembled and analyzed for the first time. These genomes were 158,290-160,042 bp in size and contained 113 non-repeat genes, including 79 protein-coding genes, 30 tRNA genes, and four rRNA genes. We also report on codon usage, RNA editing sites, microsatellite structures, and new repetitive sequences in this genus. Comparative genomics revealed that expansion and contraction of IR regions can lead to changes in the gene numbers. Additionally, it was observed that the highly variable regions of the chloroplast genome were mainly located in intergenic regions. Furthermore, the phylogenetic tree showed the order Nymphaeales was divided into three families, and the genus Nymphaea can be divided into five (or three) subgenera, with the subgenus Nymphaea being the oldest. The divergence times of nymphaealean taxa were analyzed, with origins of the order Nymphaeales and family Nymphaeaceae being about 194 and 131 million years, respectively. The results of the phylogenetic analysis and estimated divergence times will be useful for future evolutionary studies of basal angiosperm lineages.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42995-024-00242-0.

Genetic factors explaining anthocyanin pigmentation differences

BACKGROUND

Anthocyanins are important contributors to coloration across a wide phylogenetic range of plants. Biological functions of anthocyanins span from reproduction to protection against biotic and abiotic stressors. Owing to a clearly visible phenotype of mutants, the anthocyanin biosynthesis and its sophisticated regulation have been studied in numerous plant species. Genes encoding the anthocyanin biosynthesis enzymes are regulated by a transcription factor complex comprising MYB, bHLH and WD40 proteins.

RESULTS

A systematic comparison of anthocyanin-pigmented vs. non-pigmented varieties was performed within numerous plant species covering the taxonomic diversity of flowering plants. The literature was screened for cases in which genetic factors causing anthocyanin loss were reported. Additionally, transcriptomic data sets from four previous studies were reanalyzed to determine the genes possibly responsible for color variation based on their expression pattern. The contribution of different structural and regulatory genes to the intraspecific pigmentation differences was quantified. Differences concerning transcription factors are by far the most frequent explanation for pigmentation differences observed between two varieties of the same species. Among the transcription factors in the analyzed cases, MYB genes are significantly more prone to account for pigmentation differences compared to bHLH or WD40 genes. Among the structural genes, DFR genes are most often associated with anthocyanin loss.

CONCLUSIONS

These findings support previous assumptions about the susceptibility of transcriptional regulation to evolutionary changes and its importance for the evolution of novel coloration phenotypes. Our findings underline the particular significance of MYBs and their apparent prevalent role in the specificity of the MBW complex.

Assembly and comparative analysis of the first complete mitochondrial genome of the invasive water hyacinth, Eichhornia crassipes

Eichhornia crassipes is an aquatic plant in tropical and subtropical regions, renowned for its notorious invasive tendencies. In this study, we assembled the complete mitogenome of E. crassipes into a single circle molecule of 397,361 bp. The mitogenome has 58 unique genes, including 37 protein-coding genes (PCGs), 18 tRNA genes, three rRNA genes, and 47 % GC content. Sixteen (6.93 %) homologous fragments, ranging from 31 bp to 8548 bp, were identified, indicating the transfer of genetic material from chloroplasts to mitochondria. In addition, we detected positive selection in six PCGs (ccmB, ccmC, ccmFC, nad3, nad4 and sdh4), along with the identification of 782 RNA editing sites across 37 mt-PCGs. These findings suggest a potential contribution to the robust adaptation of this invasive plant to the stressful environment. Lastly, we inferred that phylogenetic conflicts of E. crassipes between the plastome and mitogenome may be attributed to the difference in nucleotide substitution rates between the two organelle genomes. In conclusion, our study provided vital genomic resources for further understanding the invasive mechanism of this species and exploring the dynamic evolution of mitogenomes within the monocot clade.

The chloroplast genome sequences of Ipomoea alba and I. obscura (Convolvulaceae): genome comparison and phylogenetic analysis

Ipomoea species have diverse uses as ornamentals, food, and medicine. However, their genomic information is limited; I. alba and I. obscura were sequenced and assembled. Their chloroplast genomes were 161,353 bp and 159,691 bp, respectively. Both genomes exhibited a quadripartite structure, consisting of a pair of inverted repeat (IR) regions, which are separated by the large single-copy (LSC) and small single-copy (SSC) regions. The overall GC content was 37.5% for both genomes. A total of 104 and 93 simple sequence repeats, 50 large repeats, and 30 and 22 short tandem repeats were identified in the two chloroplast genomes, respectively. G and T were more preferred than C and A at the third base position based on the Parity Rule 2 plot analysis, and the neutrality plot revealed correlation coefficients of 0.126 and 0.105, indicating the influence of natural selection in shaping the codon usage bias in most protein-coding genes (CDS). Genome comparative analyses using 31 selected Ipomoea taxa from Thailand showed that their chloroplast genomes are rather conserved, but the presence of expansion or contraction of the IR region was identified in some of these Ipomoea taxa. A total of five highly divergent regions were identified, including the CDS genes accD, ndhA, and ndhF, as well as the intergenic spacer regions psbI-atpA and rpl32-ccsA. Phylogenetic analysis based on both the complete chloroplast genome sequence and CDS datasets of 31 Ipomoea taxa showed that I. alba is resolved as a group member for series (ser.) Quamoclit, which contains seven other taxa, including I. hederacea, I. imperati, I. indica, I. nil, I. purpurea, I. quamoclit, and I. × sloteri, while I. obscura is grouped with I. tiliifolia, both of which are under ser. Obscura, and is closely related to I. biflora of ser. Pes-tigridis. Divergence time estimation using the complete chloroplast genome sequence dataset indicated that the mean age of the divergence for Ipomoeeae, Argyreiinae, and Astripomoeinae, was approximately 29.99 Mya, 19.81 Mya, and 13.40 Mya, respectively. The node indicating the divergence of I. alba from the other members of Ipomoea was around 10.06 Mya, and the split between I. obscura and I. tiliifolia is thought to have happened around 17.13 Mya. The split between the I. obscura accessions from Thailand and Taiwan is thought to have taken place around 0.86 Mya.

Genomic incongruence accompanies the evolution of flower symmetry in Eudicots: a case study in the poppy family (Papaveraceae, Ranunculales)

Reconstructing evolutionary trajectories and transitions that have shaped floral diversity relies heavily on the phylogenetic framework on which traits are modelled. In this study, we focus on the angiosperm order Ranunculales, sister to all other eudicots, to unravel higher-level relationships, especially those tied to evolutionary transitions in flower symmetry within the family Papaveraceae. This family presents an astonishing array of floral diversity, with actinomorphic, disymmetric (two perpendicular symmetry axes), and zygomorphic flowers. We generated nuclear and plastid datasets using the Angiosperms353 universal probe set for target capture sequencing (of 353 single-copy nuclear ortholog genes), together with publicly available transcriptome and plastome data mined from open-access online repositories. We relied on the fossil record of the order Ranunculales to date our phylogenies and to establish a timeline of events. Our phylogenomic workflow shows that nuclear-plastid incongruence accompanies topological uncertainties in Ranunculales. A cocktail of incomplete lineage sorting, post-hybridization introgression, and extinction following rapid speciation most likely explain the observed knots in the topology. These knots coincide with major floral symmetry transitions and thus obscure the order of evolutionary events.

Nuclear phylogenomics of Asteraceae with increased sampling provides new insights into convergent morphological and molecular evolution

Convergent morphological evolution is widespread in flowering plants, and understanding this phenomenon relies on well-resolved phylogenies. Nuclear phylogenetic reconstruction using transcriptome datasets has been successful in various angiosperm groups, but it is limited to taxa with available fresh materials. Asteraceae, which are one of the two largest angiosperm families and are important for both ecosystems and human livelihood, show multiple examples of convergent evolution. Nuclear Asteraceae phylogenies have resolved relationships among most subfamilies and many tribes, but many phylogenetic and evolutionary questions regarding subtribes and genera remain, owing to limited sampling. Here, we increased the sampling for Asteraceae phylogenetic reconstruction using transcriptomes and genome-skimming datasets and produced nuclear phylogenetic trees with 706 species representing two-thirds of recognized subtribes. Ancestral character reconstruction supports multiple convergent evolutionary events in Asteraceae, with gains and losses of bilateral floral symmetry correlated with diversification of some subfamilies and smaller groups, respectively. Presence of the calyx-related pappus may have been especially important for the success of some subtribes and genera. Molecular evolutionary analyses support the likely contribution of duplications of MADS-box and TCP floral regulatory genes to innovations in floral morphology, including capitulum inflorescences and bilaterally symmetric flowers, potentially promoting the diversification of Asteraceae. Subsequent divergences and reductions in CYC2 gene expression are related to the gain and loss of zygomorphic flowers. This phylogenomic work with greater taxon sampling through inclusion of genome-skimming datasets reveals the feasibility of expanded evolutionary analyses using DNA samples for understanding convergent evolution.

AcMYB266, a key regulator of the red coloration in pineapple peel: a case of subfunctionalization in tandem duplicated genes

Red fruit peel is an attractive target for pineapple breeding. Various pineapple accessions with distinct red coloration patterns exist; however, the precise molecular mechanism accounting for these differences remains unknown, which hinders the pineapple breeding process from combining high fruit quality with red peel. In this study, we characterized a transcription factor, AcMYB266, which is preferentially expressed in pineapple peel and positively regulates anthocyanin accumulation. Transgenic pineapple, Arabidopsis, and tobacco plants overexpressing AcMYB266 exhibited significant anthocyanin accumulation. Conversely, transient silencing of this gene led to decreased anthocyanin accumulation in pineapple red bracts. In-depth analysis indicated that variations of AcMYB266 sequences in the promoter instead of the protein-coding region seem to contribute to different red coloration patterns in peels of three representative pineapple varieties. In addition, we found that AcMYB266 was located in a cluster of four MYB genes exclusive to and conserved in Ananas species. Of this cluster, each was proved to regulate anthocyanin synthesis in different pineapple tissues, illustrating an interesting case of gene subfunctionalization after tandem duplication. In summary, we have characterized AcMYB266 as a key regulator of pineapple red fruit peel and identified an MYB cluster whose members were subfunctionalized to specifically regulate the red coloration of different pineapple tissues. The present study will assist in establishing a theoretical mechanism for pineapple breeding for red fruit peel and provide an interesting case for the investigation of gene subfunctionalization in plants.

Refining the phylogeny and taxonomy of the apple tribe Maleae (Rosaceae): insights from phylogenomic analyses of 563 plastomes and a taxonomic synopsis of Photinia and its allies in the Old World

This study addresses the longstanding absence of a comprehensive phylogenetic backbone for the apple tribe Maleae, a deficiency attributed to limited taxon and marker sampling. We conducted an extensive taxon sampling, incorporating 563 plastomes from a diverse range of 370 species encompassing 26 presently recognized genera. Employing a range of phylogenetic inference methods, including RAxML and IQ-TREE2 for Maximum Likelihood (ML) analyses, we established a robust phylogenetic framework for the Maleae tribe. Our phylogenomic investigations provided compelling support for three major clades within Maleae. By integrating nuclear phylogenetic data with morphological and chromosomal evidence, we propose an updated infra-tribal taxonomic system, comprising subtribe Malinae Reveal, subtribe Lindleyinae Reveal, and subtribe Vauqueliniinae B.B.Liu (subtr. nov.). Plastid phylogenetic analysis also confirmed the monophyly of most genera, except for Amelanchier, Malus, Sorbus sensu lato, and Stranvaesia. In addition, we present a comprehensive taxonomic synopsis of Photinia and its morphological allies in the Old World, recognizing 27 species and ten varieties within Photinia, three species and two varieties within Stranvaesia, and two species and three varieties within Weniomeles. Furthermore, we also lectotypified 12 names and made two new combinations, Photiniamicrophylla (J.E.Vidal) B.B.Liu and Weniomelesatropurpurea (P.L.Chiu ex Z.H.Chen & X.F.Jin) B.B.Liu.

Phylogenomics and the rise of the angiosperms

Angiosperms are the cornerstone of most terrestrial ecosystems and human livelihoods1,2. A robust understanding of angiosperm evolution is required to explain their rise to ecological dominance. So far, the angiosperm tree of life has been determined primarily by means of analyses of the plastid genome3,4. Many studies have drawn on this foundational work, such as classification and first insights into angiosperm diversification since their Mesozoic origins5-7. However, the limited and biased sampling of both taxa and genomes undermines confidence in the tree and its implications. Here, we build the tree of life for almost 8,000 (about 60%) angiosperm genera using a standardized set of 353 nuclear genes8. This 15-fold increase in genus-level sampling relative to comparable nuclear studies9 provides a critical test of earlier results and brings notable change to key groups, especially in rosids, while substantiating many previously predicted relationships. Scaling this tree to time using 200 fossils, we discovered that early angiosperm evolution was characterized by high gene tree conflict and explosive diversification, giving rise to more than 80% of extant angiosperm orders. Steady diversification ensued through the remaining Mesozoic Era until rates resurged in the Cenozoic Era, concurrent with decreasing global temperatures and tightly linked with gene tree conflict. Taken together, our extensive sampling combined with advanced phylogenomic methods shows the deep history and full complexity in the evolution of a megadiverse clade.

Unprecedented variation pattern of plastid genomes and the potential role in adaptive evolution in Poales

BACKGROUND

The plastid is the photosynthetic organelle in plant cell, and the plastid genomes (plastomes) are generally conserved in evolution. As one of the most economically and ecologically important order of angiosperms, Poales was previously documented to exhibit great plastomic variation as an order of photoautotrophic plants.

RESULTS

We acquired 93 plastomes, representing all the 16 families and 5 major clades of Poales to reveal the extent of their variation and evolutionary pattern. Extensive variation including the largest one in monocots with 225,293 bp in size, heterogeneous GC content, and a wide variety of gene duplication and loss were revealed. Moreover, rare occurrences of three inverted repeat (IR) copies in angiosperms and one IR loss were observed, accompanied by short IR (sIR) and small direct repeat (DR). Widespread structural heteroplasmy, diversified inversions, and unusual genomic rearrangements all appeared in Poales, occasionally within a single species. Extensive repeats in the plastomes were found to be positively correlated with the observed inversions and rearrangements. The variation all showed a "small-large-moderate" trend along the evolution of Poales, as well as for the sequence substitution rate. Finally, we found some positively selected genes, mainly in C4 lineages, while the closely related lineages of those experiencing gene loss tended to have undergone more relaxed purifying selection.

CONCLUSIONS

The variation of plastomes in Poales may be related to its successful diversification into diverse habitats and multiple photosynthetic pathway transitions. Our order-scale analyses revealed unusual evolutionary scenarios for plastomes in the photoautotrophic order of Poales and provided new insights into the plastome evolution in angiosperms as a whole.

Plastid phylogenomics and fossil evidence provide new insights into the evolutionary complexity of the 'woody clade' in Saxifragales

BACKGROUND

The "woody clade" in Saxifragales (WCS), encompassing four woody families (Altingiaceae, Cercidiphyllaceae, Daphniphyllaceae, and Hamamelidaceae), is a phylogenetically recalcitrant node in the angiosperm tree of life, as the interfamilial relationships of the WCS remain contentious. Based on a comprehensive sampling of WCS genera, this study aims to recover a robust maternal backbone phylogeny of the WCS by analyzing plastid genome (plastome) sequence data using Bayesian inference (BI), maximum likelihood (ML), and maximum parsimony (MP) methods, and to explore the possible causes of the phylogenetic recalcitrance with respect to deep relationships within the WCS, in combination with molecular and fossil evidence.

RESULTS

Although the four WCS families were identically resolved as monophyletic, the MP analysis recovered different tree topologies for the relationships among Altingiaceae, Cercidiphyllaceae, and Daphniphyllaceae from the ML and BI phylogenies. The fossil-calibrated plastome phylogeny showed that the WCS underwent a rapid divergence of crown groups in the early Cretaceous (between 104.79 and 100.23 Ma), leading to the origin of the stem lineage ancestors of Altingiaceae, Cercidiphyllaceae, Daphniphyllaceae, and Hamamelidaceae within a very short time span (∼4.56 Ma). Compared with the tree topology recovered in a previous study based on nuclear genome data, cytonuclear discordance regarding the interfamilial relationships of the WCS was detected.

CONCLUSIONS

Molecular and fossil evidence imply that the early divergence of the WCS might have experienced radiative diversification of crown groups, extensive extinctions at the genus and species levels around the Cretaceous/Paleocene boundary, and ancient hybridization. Such evolutionarily complex events may introduce biases in topological estimations within the WCS due to incomplete lineage sorting, cytonuclear discordance, and long-branch attraction, potentially impacting the accurate reconstruction of deep relationships.

Advances in pharmacology, biosynthesis, and metabolic engineering of Scutellaria-specialized metabolites

Scutellaria Linn., which belongs to the family Lamiaceae, is a commonly used medicinal plant for heat clearing and detoxification. In particular, the roots of S. baicalensis and the entire herb of S. barbata have been widely used in traditional medicine for thousands of years. The main active components of Scutellaria, including: baicalein, wogonin, norwogonin, scutellarein, and their glycosides have potential or existing drug usage. However, the wild resources of Scutellaria plants have been overexploited, and degenerated germplasm resources cannot fulfill the requirements of chemical extraction and clinical usage. Metabolic engineering and green production via microorganisms provide alternative strategies for greater efficiency in the production of natural products. Here, we review the progress of: pharmacological investigations, multi-omics, biosynthetic pathways, and metabolic engineering of various Scutellaria species and their active compounds. In addition, based on multi-omics data, we systematically analyze the phylogenetic relationships of Scutellaria and predict candidate transcription factors related to the regulation of active flavonoids. Finally, we propose the prospects of directed evolution of core enzymes and genome-assisted breeding to alleviate the shortage of plant resources of Scutellaria. This review provides important insights into the sustainable utilization and development of Scutellaria resources.

ORPA: a fast and efficient phylogenetic analysis method for constructing genome-wide alignments of organelle genomes

Creating a multi-gene alignment matrix for phylogenetic analysis using organelle genomes involves aligning single-gene datasets manually, a process that can be time-consuming and prone to errors. The HomBlocks pipeline has been created to eliminate the inaccuracies arising from manual operations. The processing of a large number of sequences, however, remains a time-consuming task. To conquer this challenge, we develop a speedy and efficient method called Organelle Genomes for Phylogenetic Analysis (ORPA). ORPA can quickly generate multiple sequence alignments for whole-genome comparisons by parsing the result files of NCBI BLAST, completing the task just in 1 min. With increasing data volume, the efficiency of ORPA is even more pronounced, over 300 times faster than HomBlocks in aligning 60 high-plant chloroplast genomes. The phylogenetic tree outputs from ORPA are equivalent to HomBlocks, indicating its outstanding efficiency. Due to its speed and accuracy, ORPA can identify species-level evolutionary conflicts, providing valuable insights into evolutionary cognition.

Intraspecific differentiation of Lindera obtusiloba as revealed by comparative plastomic and evolutionary analyses

Lindera obtusiloba Blume is the northernmost tree species in the family Lauraceae, and it is a key species in understanding the evolutionary history of this family. The species of L. obtusiloba in East Asia has diverged into the Northern and Southern populations, which are geographically separated by an arid belt. Though the morphological differences between populations have been observed and well documented, intraspecific variations at the plastomic level have not been systematically investigated to date. Here, ten chloroplast genomes of L. obtusiloba individuals were sequenced and analyzed along with three publicly available plastomes. Comparative plastomic analysis suggests that both the Northern and the Southern populations share similar overall structure, gene order, and GC content in their plastomes although the size of the plasome and the level of intraspecific variability do vary between the two populations. The Northern have relatively larger plastomes while the Southern population possesses higher intraspecific variability, which could be attributed to the complexity of the geological environments in the South. Phylogenomic analyses also support the split of the Northern and Southern clades among L. obtusiloba individuals. However, there is no obvious species boundary between var. obtusiloba and var. heterophylla in the Southern population, indicating that gene flow could still occur between these two varieties, and this could be used as a good example of reticulate evolution. It is also found that a few photosynthesis-related genes are under positive selection, which is mainly related to the geological and environmental differences between the Northern and the Southern regions. Our results provide a reference for phylogenetic analysis within species and suggest that phylogenomic analyses with a sufficient number of nuclear and chloroplast genomic target loci from widely distributed individuals could provide a deeper understanding of the population evolution of the widespread species.

Nuclear phylogenomics of angiosperms and insights into their relationships and evolution

Angiosperms (flowering plants) are by far the most diverse land plant group with over 300,000 species. The sudden appearance of diverse angiosperms in the fossil record was referred to by Darwin as the "abominable mystery," hence contributing to the heightened interest in angiosperm evolution. Angiosperms display wide ranges of morphological, physiological, and ecological characters, some of which have probably influenced their species richness. The evolutionary analyses of these characteristics help to address questions of angiosperm diversification and require well resolved phylogeny. Following the great successes of phylogenetic analyses using plastid sequences, dozens to thousands of nuclear genes from next-generation sequencing have been used in angiosperm phylogenomic analyses, providing well resolved phylogenies and new insights into the evolution of angiosperms. In this review we focus on recent nuclear phylogenomic analyses of large angiosperm clades, orders, families, and subdivisions of some families and provide a summarized Nuclear Phylogenetic Tree of Angiosperm Families. The newly established nuclear phylogenetic relationships are highlighted and compared with previous phylogenetic results. The sequenced genomes of Amborella, Nymphaea, Chloranthus, Ceratophyllum, and species of monocots, Magnoliids, and basal eudicots, have facilitated the phylogenomics of relationships among five major angiosperms clades. All but one of the 64 angiosperm orders were included in nuclear phylogenomics with well resolved relationships except the placements of several orders. Most families have been included with robust and highly supported placements, especially for relationships within several large and important orders and families. Additionally, we examine the divergence time estimation and biogeographic analyses of angiosperm on the basis of the nuclear phylogenomic frameworks and discuss the differences compared with previous analyses. Furthermore, we discuss the implications of nuclear phylogenomic analyses on ancestral reconstruction of morphological, physiological, and ecological characters of angiosperm groups, limitations of current nuclear phylogenomic studies, and the taxa that require future attention.

Complete Chloroplast Genomes of Four Oaks from the Section Cyclobalanopsis Improve the Phylogenetic Analysis and Understanding of Evolutionary Processes in the Genus Quercus

Quercus is a valuable genus ecologically, economically, and culturally. They are keystone species in many ecosystems. Species delimitation and phylogenetic studies of this genus are difficult owing to frequent hybridization. With an increasing number of genetic resources, we will gain a deeper understanding of this genus. In the present study, we collected four Quercus section Cyclobalanopsis species (Q. poilanei, Q. helferiana, Q. camusiae, and Q. semiserrata) distributed in Southeast Asia and sequenced their complete genomes. Following analysis, we compared the results with those of other species in the genus Quercus. These four chloroplast genomes ranged from 160,784 bp (Q. poilanei) to 161,632 bp (Q. camusiae) in length, with an overall guanine and cytosine (GC) content of 36.9%. Their chloroplast genomic organization and order, as well as their GC content, were similar to those of other Quercus species. We identified seven regions with relatively high variability (rps16, ndhk, accD, ycf1, psbZ-trnG-GCC, rbcL-accD, and rpl32-trnL-UAG) which could potentially serve as plastid markers for further taxonomic and phylogenetic studies within Quercus. Our phylogenetic tree supported the idea that the genus Quercus forms two well-differentiated lineages (corresponding to the subgenera Quercus and Cerris). Of the three sections in the subgenus Cerris, the section Ilex was split into two clusters, each nested in the other two sections. Moreover, Q. camusiae and Q. semiserrata detected in this study diverged first in the section Cyclobalanopsis and mixed with Q. engleriana in the section Ilex. In particular, 11 protein coding genes (atpF, ndhA, ndhD, ndhF, ndhK, petB, petD, rbcL, rpl22, ycf1, and ycf3) were subjected to positive selection pressure. Overall, this study enriches the chloroplast genome resources of Quercus, which will facilitate further analyses of phylogenetic relationships in this ecologically important tree genus.

Rapid in situ diversification rates in Rhamnaceae explain the parallel evolution of high diversity in temperate biomes from global to local scales

The macroevolutionary processes that have shaped biodiversity across the temperate realm remain poorly understood and may have resulted from evolutionary dynamics related to diversification rates, dispersal rates, and colonization times, closely coupled with Cenozoic climate change. We integrated phylogenomic, environmental ordination, and macroevolutionary analyses for the cosmopolitan angiosperm family Rhamnaceae to disentangle the evolutionary processes that have contributed to high species diversity within and across temperate biomes. Our results show independent colonization of environmentally similar but geographically separated temperate regions mainly during the Oligocene, consistent with the global expansion of temperate biomes. High global, regional, and local temperate diversity was the result of high in situ diversification rates, rather than high immigration rates or accumulation time, except for Southern China, which was colonized much earlier than the other regions. The relatively common lineage dispersals out of temperate hotspots highlight strong source-sink dynamics across the cosmopolitan distribution of Rhamnaceae. The proliferation of temperate environments since the Oligocene may have provided the ecological opportunity for rapid in situ diversification of Rhamnaceae across the temperate realm. Our study illustrates the importance of high in situ diversification rates for the establishment of modern temperate biomes and biodiversity hotspots across spatial scales.

Insights into the Superrosids phylogeny and flavonoid synthesis from the telomere-to-telomere gap-free genome assembly of Penthorum chinense Pursh

The completion of the first telomere-to-telomere (T2T) genome assembly of Penthorum chinense Pursh (PC), a prominent medicinal plant in China, represents a significant achievement. This assembly spans a length of 257.5 Mb and consists of nine chromosomes. PC's notably smaller genome size in Saxifragales, compared to that of Paeonia ostii, can be attributed to the low abundance of transposable elements. By utilizing single-copy genes from 30 species, including 28 other Superrosids species, we successfully resolved a previously debated Superrosids phylogeny. Our findings unveiled Saxifragales as the sister group to the core rosids, with both being the sister group to Vitales. Utilizing previously characterized cytochrome P450 (CYP) genes, we predicted the compound classes that most CYP genes of PC are involved in synthesizing, providing insight into PC's potential metabolic diversity. Metabolomic and transcriptomic data revealed that the richest sources of the three most noteworthy medicinal components in PC are young leaves and flowers. We also observed higher activity of upstream genes in the flavonoid synthesis pathway in these plant parts. Additionally, through weighted gene co-expression network analysis, we identified gene regulatory networks associated with the three medicinal components. Overall, these findings deepen our understanding of PC, opening new avenues for further research and exploration.

The complete chloroplast genome of Meconopsis bella Prain 1894 (Papaveraceae), a high-altitude plant distributed on the Qinghai-Tibet plateau

Meconopsis bella Prain 1894 (M. bella) is a rare herb within the family Papaveraceae of which unique and gorgeous purple flowers are blooming in the flowering phase. In this study, we reported the complete chloroplast (cp) genome of M. bella, which was mainly distributed on the Qinghai-Tibet plateau. The complete chloroplast genome sequence of M. bella was 153,073 bp in size and was characterized by a typical quadripartite structure consisting of a large single-copy (LSC) region of 83,562 bp, a small single-copy (SSC) region of 178,33 bp and two identical inverted repeats (IR) regions of 25,839 bp. The genome contained 133 genes, including 88 protein-encoding genes, eight ribosomal RNA genes, and 37 transfer RNA genes. Phylogenetic analysis based on the maximum-likelihood (ML) method showed that M. bella was closely related to M. paniculate and M. pinnatifolia within the genus Meconopsis.

The first mitogenome of Lauraceae (Cinnamomum chekiangense)

•The first reported mitochondrial genome (Cinnamomum chekiangense) of the Lauraceae family.•The mitogenome of C. chekiangense retains almost all of the ancestral protein-coding genes and has the highest RNA editing number in angiosperms.•Both of the plastid and mitochondrial phylogenetic trees support the magnoliids as a sister group of monocots and eudicots.

Evolution of the Araliaceae family involved rapid diversification of the Asian Palmate group and Hydrocotyle specific mutational pressure

The Araliaceae contain many valuable species in medicinal and industrial aspects. We performed intensive phylogenomics using the plastid genome (plastome) and 45S nuclear ribosomal DNA sequences. A total of 66 plastome sequences were used, 13 of which were newly assembled in this study, 12 from new sequences, and one from existing data. While Araliaceae plastomes showed conserved genome structure, phylogenetic reconstructions based on four different plastome datasets revealed phylogenetic discordance within the Asian Palmate group. The divergence time estimation revealed that splits in two Araliaceae subfamilies and the clades exhibiting phylogenetic discordances in the Asian Palmate group occurred at two climatic optima, suggesting that global warming events triggered species divergence, particularly the rapid diversification of the Asian Palmate group during the Middle Miocene. Nucleotide substitution analyses indicated that the Hydrocotyloideae plastomes have undergone accelerated AT-biased mutations (C-to-T transitions) compared with the Aralioideae plastomes, and the acceleration may occur in their mitochondrial and nuclear genomes as well. This implies that members of the genus Hydrocotyle, the only aquatic plants in the Araliaceae, have experienced a distinct evolutionary history from the other species. We also discussed the intercontinental disjunction in the genus Panax and proposed a hypothesis to complement the previously proposed hypothesis. Our results provide the evolutionary trajectory of Araliaceae and advance our current understanding of the evolution of Araliaceae species.

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.

Comparative analyses of eight complete plastid genomes of two hemiparasitic Cassytha vines in the family Lauraceae

Cassytha is the sole genus of hemiparasitic vines (ca. 20 spp.) belonging to the Cassytheae tribe of the Lauraceae family. It is extensively distributed in tropical and subtropical regions. In this study, we determined the complete plastid genome sequences of C. filiformis and C. larsenii, which do not possess the typical quadripartite structure. The length of C. filiformis plastomes ranged from 114,215 to 114,618 bp, whereas that of C. larsenii plastomes ranged from 114,900 to 114,988 bp. Comparative genomic analysis revealed 1,013 mutation sites, four large intragenomic deletions, and five highly variable regions in the eight plastome sequences. Phylogenetic analyses based on 61 complete plastomes of Laurales species, 19 ITS sequences, and trnK barcodes from 91 individuals of Cassytha spp. confirmed a non-basal group comprising individuals of C. filiformis, C. larsenii, and C. pubescens in the family Lauraceae and proposed a sister relationship between C. filiformis and C. larsenii. Further morphological comparisons indicated that the presence or absence of hairs on the haustoria and the shape or size of fruits were useful traits for differentiating C. filiformis and C. larsenii.

Nightmare or delight: Taxonomic circumscription meets reticulate evolution in the phylogenomic era

Phylogenetic studies in the phylogenomics era have demonstrated that reticulate evolution greatly impedes the accuracy of phylogenetic inference, and consequently can obscure taxonomic treatments. However, the systematics community lacks a broadly applicable strategy for taxonomic delimitation in groups characterized by pervasive reticulate evolution. The red-fruit genus, Stranvaesia, provides an ideal model to examine the influence of reticulation on generic circumscription, particularly where hybridization and allopolyploidy dominate the evolutionary history. In this study, we conducted phylogenomic analyses integrating data from hundreds of single-copy nuclear (SCN) genes and plastomes, and interrogated nuclear paralogs to clarify the inter/intra-generic relationship of Stranvaesia and its allies in the framework of Maleae. Analyses of phylogenomic discord and phylogenetic networks showed that allopolyploidization and introgression promoted the origin and diversification of the Stranvaesia clade, a conclusion further bolstered by cytonuclear and gene tree discordance. With a well-inferred phylogenetic backbone, we propose an updated generic delimitation of Stranvaesia and introduce a new genus, Weniomeles. This new genus is distinguished by its purple-black fruits, thorns trunk and/or branches, and a distinctive fruit core anatomy characterized by multilocular separated by a layer of sclereids and a cluster of sclereids at the top of the locules. Through this study, we highlight a broadly-applicable workflow that underscores the significance of reticulate evolution analyses in shaping taxonomic revisions from phylogenomic data.

Two haplotype-resolved genomes reveal important flower traits in bigleaf hydrangea (Hydrangea macrophylla) and insights into Asterid evolution

The Hydrangea genus belongs to the Hydrangeaceae family, in the Cornales order of flowering plants, which early diverged among the Asterids, and includes several species that are commonly used ornamental plants. Of them, Hydrangea macrophylla is one of the most valuable species in the nursery trade, yet few genomic resources are available for this crop or closely related Asterid species. Two high-quality haplotype-resolved reference genomes of hydrangea cultivars 'Veitchii' and 'Endless Summer' [highest quality at 2.22 gigabase pairs (Gb), 396 contigs, N50 22.8 megabase pairs (Mb)] were assembled and scaffolded into the expected 18 pseudochromosomes. Utilizing the newly developed high-quality reference genomes along with high-quality genomes of other related flowering plants, nuclear data were found to support a single divergence point in the Asterids clade where both the Cornales and Ericales diverged from the euasterids. Genetic mapping with an F1 hybrid population demonstrated the power of linkage mapping combined with the new genomic resources to identify the gene for inflorescence shape, CYP78A5 located on chromosome 4, and a novel gene, BAM3 located on chromosome 17, for causing double flower. Resources developed in this study will not only help to accelerate hydrangea genetic improvement but also contribute to understanding the largest group of flowering plants, the Asterids.

Macroevolutionary trends of the Neotropical genus Ameroglossum (Linderniaceae) in rocky outcrop environments

Ameroglossum is a rare plant genus endemic to northeastern of Brazil, initially monospecific (A. pernambucense) and recently expanded by the description of eight new species and two related genera. The genus was initially placed in the family Scrophulariaceae, but this has never been phylogenetically tested. This group is ecologically restricted to rocky inselberg habitats that function as island-like systems (ILS) with spatial fragmentation, limited area, environmental heterogeneity, temporal isolation and low connectivity. Here we use a phylogenetic perspective to test the hypothesis that Ameroglossum diversification was related to island-like radiation in inselbergs. Our results support that Ameroglossum is monophyletic only with the inclusion of Catimbaua and Isabelcristinia (named here as Ameroglossum sensu lato) and this group was well-supported in the family Linderniaceae. Biogeographic analyses suggest that the ancestral of Ameroglossum and related genus arrived in South America c.a. 15 million years ago by long-distance dispersal, given the ancestral distribution of Linderniaceae in Africa. In rocky outcrop habitats, Ameroglossum s.l. developed floral morphological specialization associated with pollinating hummingbirds, compatible with an island-like model. However, no increase in speciation rate was detected, which may be related to high extinction rates and/or slow diversification rate in this ecologically restrictive environment. Altogether, in Ameroglossum key innovations involving flowers seem to have offered opportunities for evolution of greater phenotypic diversity and occupation of new niches in rocky outcrop environments.

Dispersal modes affect Rhamnaceae diversification rates in a differentiated manner

The evolution of dispersal modes has been proposed to promote the diversification of angiosperms. However, little is known about the relative impact of different dispersal modes on plant diversification. We test the association between dispersal modes and diversification rates using Rhamnaceae, the cosmopolitan buckthorn family, as a model. We found that species with diplochory have the highest diversification rates followed by those with myrmecochory and ballistic dispersal, while lineages dispersed by vertebrates and wind have relatively low diversification rates. The difference in diversification rates may be closely linked to the difference in dispersal distance and ecological interactions implied by each dispersal mode. Species which disperse over larger geographical distances may have much higher speciation rates due to the increased chance of establishing isolated populations due to geological barriers or habitat fragmentation. However, long-distance dispersal may also increase the chance of extinction. By contrast, species with short-distance dispersal modes may have low speciation rates. Complex interactions with the surrounding environment may, however, impact diversification rates positively by increasing plant survival and reproductive success.

Complete Plastid Genomes of Nine Species of Ranunculeae (Ranunculaceae) and Their Phylogenetic Inferences

The tribe Ranunculeae, Ranunculaceae, comprising 19 genera widely distributed all over the world. Although a large number of Sanger sequencing-based molecular phylogenetic studies have been published, very few studies have been performed on using genomic data to infer phylogenetic relationships within Ranunculeae. In this study, the complete plastid genomes of nine species (eleven samples) from Ceratocephala, Halerpestes, and Ranunculus were de novo assembled using a next-generation sequencing method. Previously published plastomes of Oxygraphis and other related genera of the family were downloaded from GenBank for comparative analysis. The complete plastome of each Ranunculeae species has 112 genes in total, including 78 protein-coding genes, 30 transfer RNA genes, and four ribosomal RNA genes. The plastome structure of Ranunculeae samples is conserved in gene order and arrangement. There are no inverted repeat (IR) region expansions and only one IR contraction was found in the tested samples. This study also compared plastome sequences across all the samples in gene collinearity, codon usage, RNA editing sites, nucleotide variability, simple sequence repeats, and positive selection sites. Phylogeny of the available Ranunculeae species was inferred by the plastome data using maximum-likelihood and Bayesian inference methods, and data partitioning strategies were tested. The phylogenetic relationships were better resolved compared to previous studies based on Sanger sequencing methods, showing the potential value of the plastome data in inferring the phylogeny of the tribe.

Complete plastid genome structure of 13 Asian Justicia (Acanthaceae) species: comparative genomics and phylogenetic analyses

BACKGROUND

Justicia L. is the largest genus in Acanthaceae Juss. and widely distributed in tropical and subtropical regions of the world. Previous phylogenetic studies have proposed a general phylogenetic framework for Justicia based on several molecular markers. However, their studies were mainly focused on resolution of phylogenetic issues of Justicia in Africa, Australia and South America due to limited sampling from Asia. Additionally, although Justicia plants are of high medical and ornamental values, little research on its genetics was reported. Therefore, to improve the understanding of its genomic structure and relationships among Asian Justicia plants, we sequenced complete chloroplast (cp.) genomes of 12 Asian plants and combined with the previously published cp. genome of Justicia leptostachya Hemsl. for further comparative genomics and phylogenetic analyses.

RESULTS

All the cp. genomes exhibit a typical quadripartite structure without genomic rearrangement and gene loss. Their sizes range from 148,374 to 151,739 bp, including a large single copy (LSC, 81,434-83,676 bp), a small single copy (SSC, 16,833-17,507 bp) and two inverted repeats (IR, 24,947-25,549 bp). GC contents range from 38.1 to 38.4%. All the plastomes contain 114 genes, including 80 protein-coding genes, 30 tRNAs and 4 rRNAs. IR variation and repetitive sequences analyses both indicated that Justicia grossa C. B. Clarke is different from other Justicia species because its lengths of ndhF and ycf1 in IRs are shorter than others and it is richest in SSRs and dispersed repeats. The ycf1 gene was identified as the candidate DNA barcode for the genus Justicia. Our phylogenetic results showed that Justicia is a polyphyletic group, which is consistent with previous studies. Among them, J. grossa belongs to subtribe Tetramerinae of tribe Justicieae while the other Justicia members belong to subtribe Justiciinae. Therefore, based on morphological and molecular evidence, J. grossa should be undoubtedly recognized as a new genus. Interestingly, the evolutionary history of Justicia was discovered to be congruent with the morphology evolution.

CONCLUSION

Our study not only elucidates basic features of Justicia whole plastomes, but also sheds light on interspecific relationships of Asian Justicia plants for the first time.

First record of the genus Camptotheca (Nyssaceae) in Vietnam and the lectotypification of C.acuminata

As a primary source of anticancer camptothecin, Camptotheca (Nyssaceae) is an economically valuable genus and has long been recorded as endemic to China. Here, Camptotheca is reported as a new record to the flora of Vietnam with the discovery of a wild population of C.acuminata from Lai Chau Province of northern Vietnam. Based on the consultation of relevant literature and type specimens of C.acuminata, a lectotype of the species is designated. Photographic illustrations, morphological description and a distribution map of C.acuminata is provided, and a key to all known species of Nyssaceae in Vietnam is presented, too.

A comprehensive evaluation of flowering plant diversity and conservation priority for national park planning in China

Establishment of a national park protection system in China, including the latest target proposed to protect at least 30% of the land area, calls for a comprehensive exploration of conservation priorities incorporating multiple diversity facets. We herein evaluate the spatial distribution of Chinese flowering plants from the perspectives of richness, uniqueness, vulnerability, and evolutionary history, by integrating three mega-phylogenies and comprehensive distribution data. We detect significantly high consistency among hotspots of different diversity measures for Chinese flowering plants, suggesting that multiple facets of evolutionary diversity are concentrically distributed in China. Affording legal protection to these areas is expected to maximize positive conservation outcomes. We propose two integrative diversity indices by incorporating three richness-based and three phylogeny-based measures, respectively. Both methods identify areas with high species richness, but the integrative phylogeny-based index also locates key areas with ancient and unique evolutionary histories (e.g., Ailao-Wuliang Mts, Dabie Mts, Hainan rainforest, Karst area of Yunnan-Guizhou-Guangxi, Nanling Mts, and southeast coastal regions). Of all the diversity indices explored, phylogenetic endemism maximizes the incidental protection of other indices in most cases, emphasizing its significance for conservation planning. Finally, 42 priority areas are identified by combining the 5%-criterion hotspots of two integrative indices and the minimum area to protect all threatened species analyzed. These priorities cover only 13.3% of China's land area, but host 97.1% of species richness (23,394/24,095), 96.5% of endemic species (11,841/12,274), 100% of threatened species (2,613/2,613), and 99.3% of phylogenetic diversity for flowering plants involved in this study. These frameworks provide a solid scientific basis for national park planning in China.