Asterid Phylogenomics/Phylotranscriptomics Uncover Morphological Evolutionary Histories and Support Phylogenetic Placement for Numerous Whole-Genome Duplications

Pan-genome analysis reveals the evolution and diversity of Malus

Malus Mill., a genus of temperate perennial trees with great agricultural and ecological value, has diversified through hybridization, polyploidy and environmental adaptation. Limited genomic resources for wild Malus species have hindered the understanding of their evolutionary history and genetic diversity. We sequenced and assembled 30 high-quality Malus genomes, representing 20 diploids and 10 polyploids across major evolutionary lineages and geographical regions. Phylogenomic analyses revealed ancient gene duplications and conversions, while six newly defined genome types, including an ancestral type shared by polyploid species, facilitated the detection of strong signals for extensive introgressions. The graph-based pan-genome captured shared and species-specific structural variations, facilitating the development of a molecular marker for apple scab resistance. Our pipeline for analyzing selective sweep identified a mutation in MdMYB5 having reduced cold and disease resistance during domestication. This study advances Malus genomics, uncovering genetic diversity and evolutionary insights while enhancing breeding for desirable traits.

Telomere-to-telomere genome assembly and 3D chromatin architecture of Centella asiatica insight into evolution and genetic basis of triterpenoid saponin biosynthesis

Centella asiatica is renowned for its medicinal properties, particularly due to its triterpenoid saponins, such as asiaticoside and madecassoside, which are in excess demand for the cosmetic industry. However, comprehensive genomic resources for this species are lacking, which impedes the understanding of its biosynthetic pathways. Here, we report a telomere-to-telomere (T2T) C. asiatica genome. The genome size is 438.12 Mb with a contig N50 length of 54.12 Mb. The genome comprises 258.87 Mb of repetitive sequences and 25 200 protein-coding genes. Comparative genomic analyses revealed C. asiatica as an early-diverging genus within the Apiaceae family with a single whole-genome duplication (WGD, Apiaceae-ω) event following the ancient γ-triplication, contrasting with Apiaceae species that exhibit two WGD events (Apiaceae-α and Apiaceae-ω). We further constructed 3D chromatin structures, A/B compartments, and topologically associated domains (TADs) in C. asiatica leaves, elucidating the influence of chromatin organization on expression WGD-derived genes. Additionally, gene family and functional characterization analysis highlight the key role of CasiOSC03 in α-amyrin production while also revealing significant expansion and high expression of CYP716, CYP714, and UGT73 families involved in asiaticoside biosynthesis compared to other Apiaceae species. Notably, a unique and large UGT73 gene cluster, located within the same TAD, is potentially pivotal for enhancing triterpenoid saponin. Weighted gene coexpression network analysis (WGCNA) further highlighted the pathways modulated in response to methyl jasmonate (MeJA), offering insights into the regulatory networks governing saponin biosynthesis. This work not only provides a valuable genomic resource for C. asiatica but also sheds light on the molecular mechanisms driving the biosynthesis of pharmacologically important metabolites.

SOI: robust identification of orthologous synteny with the Orthology Index and broad applications in evolutionary genomics

With the explosive growth of whole-genome datasets, accurate detection of orthologous synteny has become crucial for reconstructing evolutionary history. However, current methods for identifying orthologous synteny face great limitations, particularly in scaling with varied polyploidy histories and accurately removing out-paralogous synteny. In this study, we developed a scalable and robust approach, based on the Orthology Index (OI), to effectively identify orthologous synteny. Our evaluation across a large-scale empirical dataset with diverse polyploidization events demonstrated the high reliability and robustness of the OI method. Simulation-based benchmarks further validated the accuracy of our method, showing its superior performance against existing methods across a wide range of scenarios. Additionally, we explored its broad applications in reconstructing the evolutionary histories of plant genomes, including the inference of polyploidy, identification of reticulation, and phylogenomics. In conclusion, OI offers a robust, interpretable, and scalable approach for identifying orthologous synteny, facilitating more accurate and efficient analyses in plant evolutionary genomics.

Genome assembly of Stewartia sinensis reveals origin and evolution of orphan genes in Theaceae

Orphan genes play crucial roles in diverse biological processes, but the evolutionary trajectories and functional divergence remain largely unexplored. The Theaceae family, including the economically and culturally important tea plant, offers a distinctive model to examine these aspects. Here, we integrated Nanopore long-read sequencing, Illumina short-read sequencing, and Hi-C methods to decode a pseudo-chromosomal genome assembly of Stewartia sinensis, from the earliest-diverging tribe of Theaceae, spanning 2.95 Gb. Comparative genomic analysis revealed the absence of recent whole-genome duplication events in the Theaceae ancestor, highlighting tandem duplications as the predominant mechanism of gene expansion. We identified 31,331 orphan genes, some of which appear to have ancient origins, suggesting early emergence with frequent gains and losses, while others seem more specific and recent. Notably, orphan genes are distinguished by shorter lengths, fewer exons and functional domains compared to genes that originate much earlier, like transcription factors. Moreover, tandem duplication contributes significantly to the adaptive evolution and characteristic diversity of Theaceae, and it is also a major mechanism driving the origination of orphan genes. This study illuminates the evolutionary dynamics of orphan genes, providing a valuable resource for understanding the origin and evolution of tea plant flavor and enhancing genetic breeding efforts.

Tracing the path from conservation to expansion evolutionary insights into NLR genes in oleaceae

The Oleaceae family, encompassing key genera such as Fraxinus (ash trees), Olea (olives), Jasminum (jasmine), Syringa (lilac), and Forsythia, plays a crucial ecological and economic role. Despite their importance, the evolutionary dynamics and immune system adaptations of their NLR (Nucleotide binding leucine-rich repeats) gene family remain largely unexplored. This study employs high-throughput comparative genomics to investigate NLR gene evolution across the Oleaceae family. The genus Fraxinus is widely distributed across both the New and Old Worlds, with 23 distinct species analyzed in this study. Our results reveal a predominant strategy of gene conservation in the evolution of the NLR gene family across these species. Geographical adaptation has played a significant role, particularly in Old World ash tree species, which exhibit dynamic patterns of gene expansion and contraction within the last 50 million years. Notably, genes acquired from an ancient whole genome duplication event (~ 35 Mya) have been retained across Fraxinus lineages. In contrast, the genus Olea (olives) has undergone extensive gene expansion driven by recent duplications and significant birth of novel NLR gene families. These differences in NLR gene evolution likely enhance Olea's ability to recognize diverse pathogens through recent expansions, while Fraxinus maintains specialized immune responses through conserved genes, with potential trade-offs in pathogen adaptation and energy efficiency. In terms of NLR distribution, all species of the Oleaceae family show an enhanced pseudogenization of TIR-NLRs and expansion in CCG10-NLR. However, the comparative RNA-seq expression analysis in olive suggests that partial NLR genes, despite their incomplete structure, have significant expression and may play important roles in plant immune responses. This study provides a comprehensive analysis of NLR gene evolution within the Oleaceae family, offering insights into the adaptive mechanisms of immune response evolution across diverse genera.

Structure and evolution of the Forsythieae genome elucidated by chromosome-level genome comparison of Abeliophyllum distichum and Forsythia ovata (Oleaceae)

Abeliophyllum distichum and Forsythia ovata are two closely related ornamental species of the tribe Forsythieae (Oleaceae) native to Korea. Here we report their genomic characteristics, highlighting genetic differences contributing to variations in corolla coloration, genomic variations associated with heterostyly, and the reconstruction of their ancestral karyotypes. Genome comparison revealed that A. distichum had a more compact organization of gene space than F. ovata. Centromeres of both species were enriched in Forsythieae-specific satellite repeats, hAT-Ac and MuLE-MuDR DNA transposons, and OTA-Athila Ty3/Gypsy retrotransposons. Transcriptome analysis revealed spatially differential expression of carotenoid biosynthesis-related genes in A. distichum, with downregulation in the white lobe and upregulation in the yellow base. Genome-wide analysis of structural variation in A. distichum identified retrotransposon insertions in the promoter region of an AGAMOUS homolog in the thrum plant, which showed significant downregulation of the gene compared to the pin plant. Evolutionary analyses suggested that the Oleaceae genomes evolved from 13 ancestral karyotypes via lineage-specific genomic events, including chromosome recombination, rearrangement, and whole-genome duplication followed by diploidization. The divergence of A. distichum and F. ovata was estimated to have occurred 13.87 million years ago during the Miocene epoch.

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.

Exploring Structural Plastome Evolution in Asterales: Insights from Off-Target Hybrid Enrichment Data on the Small Single-Copy Region

The massive increase in the amount of plastid genome data have allowed researchers to address a variety of evolutionary questions within a wide range of plant groups. While plastome structure is generally conserved, some angiosperm lineages exhibit structural changes. Such is the case of the megadiverse order Asterales, where rearrangements in plastome structure have been documented. This study investigates the possibility of recovering plastid loci from off-target reads obtained through hybrid enrichment techniques. Our sampling includes 63 species from the eleven currently recognized families in Asterales derived from previously published studies. We assembled and annotated complete and partial plastomes using custom pipelines and estimate phylogenomic relationships. We retrieved plastid information from 60 of the 63 sampled species including a complete plastome from Tithonia tubaeformis (Asteraceae), circular partial (with gaps) plastomes from seven species, and non-circular partial plastomes from other 52 species. We focused on the small single-copy region because it could be recovered for over 29 species. Within the small single-copy region, we assessed intron losses and presence of putative pseudogenes. Comparative genomics revealed a relocated fragment of ~ 6500 bp in two Campanulaceae lineages (i. e. subfamily Lobelioideae and Pseudonemacladus oppositifolium), involving the genes rbcL, atpB, atpE, trnM-CAU, and trnV-UAC. Obtained phylogenetic hypotheses were congruent across the applied methods and consistent with previously published results. Our study demonstrates the feasibility of recovering plastid information, both complete and partial, from off-target hybrid enrichment data and provides insights on the structural plastome changes that have occurred throughout the evolution of the order Asterales.

Yerba mate (Ilex paraguariensis) genome provides new insights into convergent evolution of caffeine biosynthesis

Yerba mate (YM, Ilex paraguariensis) is an economically important crop marketed for the elaboration of mate, the third-most widely consumed caffeine-containing infusion worldwide. Here, we report the first genome assembly of this species, which has a total length of 1.06 Gb and contains 53,390 protein-coding genes. Comparative analyses revealed that the large YM genome size is partly due to a whole-genome duplication (Ip-α) during the early evolutionary history of Ilex, in addition to the hexaploidization event (γ) shared by core eudicots. Characterization of the genome allowed us to clone the genes encoding methyltransferase enzymes that catalyse multiple reactions required for caffeine production. To our surprise, this species has converged upon a different biochemical pathway compared to that of coffee and tea. In order to gain insight into the structural basis for the convergent enzyme activities, we obtained a crystal structure for the terminal enzyme in the pathway that forms caffeine. The structure reveals that convergent solutions have evolved for substrate positioning because different amino acid residues facilitate a different substrate orientation such that efficient methylation occurs in the independently evolved enzymes in YM and coffee. While our results show phylogenomic constraint limits the genes coopted for convergence of caffeine biosynthesis, the X-ray diffraction data suggest structural constraints are minimal for the convergent evolution of individual reactions.

AMIR: a multi-omics data platform for Asteraceae plants genetics and breeding research

As the largest family of dicotyledon, the Asteraceae family comprises a variety of economically important crops, ornamental plants and numerous medicinal herbs. Advancements in genomics and transcriptomic have revolutionized research in Asteraceae species, generating extensive omics data that necessitate an efficient platform for data integration and analysis. However, existing databases face challenges in mining genes with specific functions and supporting cross-species studies. To address these gaps, we introduce the Asteraceae Multi-omics Information Resource (AMIR; https://yanglab.hzau.edu.cn/AMIR/), a multi-omics hub for the Asteraceae plant community. AMIR integrates diverse omics data from 74 species, encompassing 132 genomes, 4 408 432 genes annotated across seven different perspectives, 3897 transcriptome sequencing samples spanning 131 organs, tissues and stimuli, 42 765 290 unique variants and 15 662 metabolites genes. Leveraging these data, AMIR establishes the first pan-genome, comparative genomics and transcriptome system for the Asteraceae family. Furthermore, AMIR offers user-friendly tools designed to facilitate extensive customized bioinformatics analyses. Two case studies demonstrate AMIR's capability to provide rapid, reproducible and reliable analysis results. In summary, by integrating multi-omics data of Asteraceae species and developing powerful analytical tools, AMIR significantly advances functional genomics research and contributes to breeding practices of Asteraceae.

A chromosome-level genome of Lobelia seguinii provides insights into the evolution of Campanulaceae and the lobeline biosynthesis

Lobelia seguinii is a plant with great ecological and medicinal value and belongs to Campanulaceae. Lobelia contains lobeline, a well-known compound used to treat respiratory diseases. Nevertheless, lobeline biosynthesis needs further exploration. Moreover, whole-genome duplication (WGD) and karyotype evolution within Campanulaceae still need to be better understood. In this study, we obtained a chromosome-level genome of L. seguinii with a size of 1.4 Gb and 38253 protein-coding genes. Analyses revealed two WGDs within Campanulaceae, one at the most recent common ancestor (MRCA) of Campanula and Adenophora, and another at the MRCA of Lobelioideae. Analyses further revealed that the karyotype of Platycodon grandiflorus represents the ancient type within Asterales. We proposed eight enzymes involved in the lobeline biosynthesis pathway of L. seguinii. Molecular cloning and heterologous expression of phenylalanine ammonia-lyase (PAL), a candidate enzyme involved in the first step of lobeline biosynthesis, verified its function to catalyze the deamination of phenylalanine to cinnamic acid. This study sheds light on the evolution of Campanulaceae and lobeline biosynthesis.

Insights from the first chromosome-level genome assembly of the alpine gentian Gentiana straminea Maxim

Gentiana straminea Maxim. is a perennial herb and mainly distributed in the Qinghai-Tibetan Plateau. To adapt to the extreme environment, it has developed particular morphological, physiological, and genetic structures. Also, rich in iridoids, it is one of the original plants of traditional Chinese herb 'Qinjiao'. Herein, we present its first chromosome-level genome sequence assembly and compare it with the genomes of other Gentiana species to facilitate the analysis of genomic characteristics. The assembled genome size of G. straminea was 1.25 Gb, with a contig N50 of 7.5 Mb. A total of 96.08% of the genome sequences was anchored on 13 pseudochromosomes, with a scaffold N50 of 92.70 Mb. A total of 54,310 protein-coding genes were predicted, 80.25% of which were functionally annotated. Comparative genomic analyses indicated that G. straminea experienced two whole-genome duplication events after the γ whole-genome triplication with other eudicots, and it diverged from other Gentiana species at ~3.2 Mya. A total of 142 enzyme-coding genes related to iridoid biosynthesis were identified in its genome. Additionally, we identified differences in the number and expression patterns of iridoid biosynthetic pathway genes in G. straminea compared with two other Gentiana species by integrating whole-genome sequence and transcriptomic analyses.

The genomes of seven economic Caesalpinioideae trees provide insights into polyploidization history and secondary metabolite biosynthesis

The Caesalpinioideae subfamily contains many well-known trees that are important for economic sustainability and human health, but a lack of genomic resources has hindered their breeding and utilization. Here, we present chromosome-level reference genomes for the two food and industrial trees Gleditsia sinensis (921 Mb) and Biancaea sappan (872 Mb), the three shade and ornamental trees Albizia julibrissin (705 Mb), Delonix regia (580 Mb), and Acacia confusa (566 Mb), and the two pioneer and hedgerow trees Leucaena leucocephala (1338 Mb) and Mimosa bimucronata (641 Mb). Phylogenetic inference shows that the mimosoid clade has a much higher evolutionary rate than the other clades of Caesalpinioideae. Macrosynteny comparison suggests that the fusion and breakage of an unstable chromosome are responsible for the difference in basic chromosome number (13 or 14) for Caesalpinioideae. After an ancient whole-genome duplication (WGD) shared by all Caesalpinioideae species (CWGD, ∼72.0 million years ago [MYA]), there were two recent successive WGD events, LWGD-1 (16.2-19.5 MYA) and LWGD-2 (7.1-9.5 MYA), in L. leucocephala. Thereafter, ∼40% gene loss and genome-size contraction have occurred during the diploidization process in L. leucocephala. To investigate secondary metabolites, we identified all gene copies involved in mimosine metabolism in these species and found that the abundance of mimosine biosynthesis genes in L. leucocephala largely explains its high mimosine production. We also identified the set of all potential genes involved in triterpenoid saponin biosynthesis in G. sinensis, which is more complete than that based on previous transcriptome-derived unigenes. Our results and genomic resources will facilitate biological studies of Caesalpinioideae and promote the utilization of valuable secondary metabolites.

The long and tortuous path towards improving photosynthesis by engineering elevated mesophyll conductance

The growing demand for global food production is likely to be a defining issue facing humanity over the next 50 years. To tackle this challenge, there is a desire to bioengineer crops with higher photosynthetic efficiencies, to increase yields. Recently, there has been a growing interest in engineering leaves with higher mesophyll conductance (gm), which would allow CO2 to move more efficiently from the substomatal cavities to the chloroplast stroma. However, if crop yield gains are to be realised through this approach, it is essential that the methodological limitations associated with estimating gm are fully appreciated. In this review, we summarise these limitations, and outline the uncertainties and assumptions that can affect the final estimation of gm. Furthermore, we critically assess the predicted quantitative effect that elevating gm will have on assimilation rates in crop species. We highlight the need for more theoretical modelling to determine whether altering gm is truly a viable route to improve crop performance. Finally, we offer suggestions to guide future research on gm, which will help mitigate the uncertainty inherently associated with estimating this parameter.

Complete plastome genomes of three medicinal heliotropiaceae species: comparative analyses and phylogenetic relationships

BACKGROUND

Heliotropiaceae is a family of the order Boraginales and has over 450 species. The members of the family Heliotropiaceae have been widely reported to be used in traditional medicine Over time, the classification of Heliotropiaceae has remained uncertain and has moved from family to subfamily, or conversely.

RESULTS

In the present study, we sequenced, analyzed, and compared the complete plastomes of Euploca strigosa, Heliotropium arbainense, and Heliotropium longiflorum with the genomes of related taxa. The lengths of the plastomes of E. strigosa, H. arbainense, and H. longiflorum were 155,174 bp, 154,709 bp, and 154,496 bp, respectively. Each plastome consisted of 114 genes: 80 protein-coding genes, 4 ribosomal RNA genes, and 30 transfer RNA genes. The long repeats analysis indicated that reverse, palindromic, complement and forward repeats were all found in the three plastomes. The simple repeats analysis showed that the plastomes of E. strigosa, H. arbainense, and H. longiflorum contained 158, 165, and 151 microsatellites, respectively. The phylogenetic analysis confirmed two major clades in the Boraginales: clade I comprised Boraginaceae, while clade II included Heliotropiaceae, Ehretiaceae, Lennoaceae, and Cordiaceae. Inside the family Heliotropiaceae, E. strigosa is nested within the Heliotropium genus.

CONCLUSIONS

This study expands our knowledge of the evolutionary relationships within Heliotropiaceae and offers useful genetic resources.

Chromosome-level genome assembly of Helwingia omeiensis: the first genome in the family Helwingiaceae

Helwingia, a shrub of the monotypic cosmopolitan family Helwingiaceae, is distinguished by its inflorescence, in which flowers are borne on the midrib of the leaf-a trait not commonly observed in related plant families. Previous studies have investigated the development of this unusual structure using comparative anatomical methods. However, the scarcity of genomic data has hindered our understanding of the origins and evolutionary history of this uncommon trait at the molecular level. Here, we report the first high-quality genome of the family Helwingiaceae. Assembled using HiFi sequencing and Hi-C technologies, the genome of H. omeiensis is anchored to 19 chromosomes, with a total length of 2.75 Gb and a contig N50 length of 6.78 Mb. The BUSCO completeness score of the assembled genome was 98.2%. 53,951 genes were identified, of which 99.7% were annotated in at least one protein database. The high-quality reference genome of H. omeiensis provides an essential genetic resource and sheds light on the phylogeny and evolution of specific traits in the family Helwingiaceae.

Phylogenomic analysis and molecular identification of true fruit flies

The family Tephritidae in the order Diptera, known as true fruit flies, are agriculturally important insect pests. However, the phylogenetic relationships of true fruit flies, remain controversial. Moreover, rapid identification of important invasive true fruit flies is essential for plant quarantine but is still challenging. To this end, we sequenced the genome of 16 true fruit fly species at coverage of 47-228×. Together with the previously reported genomes of nine species, we reconstructed phylogenetic trees of the Tephritidae using benchmarking universal single-copy ortholog (BUSCO), ultraconserved element (UCE) and anchored hybrid enrichment (AHE) gene sets, respectively. The resulting trees of 50% taxon-occupancy dataset for each marker type were generally congruent at 88% nodes for both concatenation and coalescent analyses. At the subfamily level, both Dacinae and Trypetinae are monophyletic. At the species level, Bactrocera dorsalis is more closely related to Bactrocera latifrons than Bactrocera tryoni. This is inconsistent with previous conclusions based on mitochondrial genes but consistent with recent studies based on nuclear data. By analyzing these genome data, we screened ten pairs of species-specific primers for molecular identification of ten invasive fruit flies, which PCR validated. In summary, our work provides draft genome data of 16 true fruit fly species, addressing the long-standing taxonomic controversies and providing species-specific primers for molecular identification of invasive fruit flies.

Probing of plant transcriptomes reveals the hidden genetic diversity of the family Secoviridae

Secoviruses are single-stranded RNA viruses that infect plants. In the present study, we identified 61 putative novel secoviral genomes in various plant species by mining publicly available plant transcriptome data. These viral sequences represent the genomes of 13 monopartite and 48 bipartite secovirids. The genome sequences of 52 secovirids were coding-complete, and nine were partial. Except for small open reading frames (ORFs) determined in waikaviral genomes and RNA2 of torradoviruses, all of the recovered genomes/genome segments contained a large ORF encoding a polyprotein. Based on genome organization and phylogeny, all but three of the novel secoviruses were assigned to different genera. The genome organization of two identified waika-like viruses resembled that of the recently identified waika-like virus Triticum aestivum secovirus. Phylogenetic analysis revealed a pattern of host-virus co-evolution in a few waika- and waika-like viruses and increased phylogenetic diversity of nepoviruses. The study provides a basis for further investigation of the biological properties of these novel secoviruses.

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.

A hemizygous supergene controls homomorphic and heteromorphic self-incompatibility systems in Oleaceae

Self-incompatibility (SI) has evolved independently multiple times and prevents self-fertilization in hermaphrodite angiosperms. Several groups of Oleaceae such as jasmines exhibit distylous flowers, with two compatibility groups each associated with a specific floral morph.1 Other Oleaceae species in the olive tribe have two compatibility groups without associated morphological variation.2,3,4,5 The genetic basis of both homomorphic and dimorphic SI systems in Oleaceae is unknown. By comparing genomic sequences of three olive subspecies (Olea europaea) belonging to the two compatibility groups, we first locate the genetic determinants of SI within a 700-kb hemizygous region present only in one compatibility group. We then demonstrate that the homologous hemizygous region also controls distyly in jasmine. Phylogenetic analyses support a common origin of both systems, following a segmental genomic duplication in a common ancestor. Examination of the gene content of the hemizygous region in different jasmine and olive species suggests that the mechanisms determining compatibility groups and floral phenotypes (whether homomorphic or dimorphic) in Oleaceae rely on the presence/absence of two genes involved in gibberellin and brassinosteroid regulation.

Decoding Evolution of Rubioideae: Plastomes Reveal Sweet Secrets of Codon Usage, Diagnostides, and Superbarcoding

Galium genus belongs to the Rubiaceae family, which consists of approximately 14,000 species. In comparison to its well-known relatives, the plastomes of the Galium genus have not been explored so far. The plastomes of this genus have a typical, quadripartite structure, but differ in gene content, since the infA gene is missing in Galium palustre and Galium trfidum. An evaluation of the effectiveness of using entire chloroplast genome sequences as superbarcodes for accurate plant species identification revealed the high potential of this method for molecular delimitation within the genus and tribe. The trnE-UUC-psbD region showed the biggest number of diagnostides (diagnostic nucleotides) which might be new potential barcodes, not only in Galium, but also in other closely related genera. Relative synonymous codon usage (RSCU) appeared to be connected with the phylogeny of the Rubiaceae family, showing that during evolution, plants started preferring specific codons over others.

Phylogenomic profiles of whole-genome duplications in Poaceae and landscape of differential duplicate retention and losses among major Poaceae lineages

Poaceae members shared a whole-genome duplication called rho. However, little is known about the evolutionary pattern of the rho-derived duplicates among Poaceae lineages and implications in adaptive evolution. Here we present phylogenomic/phylotranscriptomic analyses of 363 grasses covering all 12 subfamilies and report nine previously unknown whole-genome duplications. Furthermore, duplications from a single whole-genome duplication were mapped to multiple nodes on the species phylogeny; a whole-genome duplication was likely shared by woody bamboos with possible gene flow from herbaceous bamboos; and recent paralogues of a tetraploid Oryza are implicated in tolerance of seawater submergence. Moreover, rho duplicates showing differential retention among subfamilies include those with functions in environmental adaptations or morphogenesis, including ACOT for aquatic environments (Oryzoideae), CK2β for cold responses (Pooideae), SPIRAL1 for rapid cell elongation (Bambusoideae), and PAI1 for drought/cold responses (Panicoideae). This study presents a Poaceae whole-genome duplication profile with evidence for multiple evolutionary mechanisms that contribute to gene retention and losses.

Development and evolution of the Asteraceae capitulum

Asteraceae represent one of the largest and most diverse families of plants. The evolutionary success of this family has largely been contributed to their unique inflorescences, capitula that mimic solitary flowers but are typically aggregates of multiple florets. Here, we summarize the recent molecular and genetic level studies that have promoted our understanding of the development and evolution of capitula. We focus on new results on patterning of the enlarged meristem resulting in the iconic phyllotactic arrangement of florets in Fibonacci numbers of spirals. We also summarize the current understanding of the genetic networks regulating the characteristic reproductive traits in the family such as floral dimorphism and differentiation of highly specialized floral organs. So far, developmental studies in Asteraceae are still limited to a very narrow selection of model species. Along with the recent advancements in genomics and phylogenomics, Asteraceae and its relatives provide an outstanding model clade for extended evo-devo studies to exploit the morphological diversity and the underlying molecular networks and to translate this knowledge to the breeding of the key crops in the family.

Influence of sample preparation methods on FTIR spectra for taxonomic identification of tropical trees in the Atlantic forest

The Atlantic forest is one of the world's major tropical biomes due to its rich biodiversity. Its vast diversity of plant species poses challenges in floristic surveys. Fourier transform infrared spectroscopy (FTIR) enables rapid and residue-free data collection, providing diverse applications in organic sample analysis. FTIR spectra quality depends on the sample preparation methodology. However, no research on FTIR spectroscopy methodology for taxonomy has been conducted with tropical tree species. Hence, this study addresses the sample preparation influence on FTIR spectra for the taxonomic classification of 12 tree species collected in the Serra do Mar State Park (PESM) - Cunha Nucleus - São Paulo State, Brazil. Spectra were obtained from intact fresh (FL), intact dried (DL), and heat-dried ground (GL) leaves. The spectra were evaluated through chemometrics using Principal Component Analysis (PCA), Hierarchical Cluster Analysis (HCA), and Linear Discriminant Analysis (LDA) with validation by LDA-PCA. The results demonstrate that sample preparation directly influences tropical species FTIR spectra categorization capability. The best taxonomic classification result for all techniques, validated by LDA-PCA, was obtained from GL. FTIR spectra evaluation through PCA, HCA, and LDA allow for the observation of phylogenetic relationships among the species. FTIR spectroscopy proves to be a viable technique for taxonomic evaluation of tree species in floristic exploration of tropical biomes which can complement traditional tools used for taxonomic studies.

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.

Whole Genome Duplication Events Likely Contributed to the Aquatic Adaptive Evolution of Parkerioideae

As the only aquatic lineage of Pteridaceae, Parkerioideae is distinct from many xeric-adapted species of the family and consists of the freshwater Ceratopteris species and the only mangrove ferns from the genus Acrostichum. Previous studies have shown that whole genome duplication (WGD) has occurred in Parkerioideae at least once and may have played a role in their adaptive evolution; however, more in-depth research regarding this is still required. In this study, comparative and evolutionary transcriptomics analyses were carried out to identify WGDs and explore their roles in the environmental adaptation of Parkerioideae. Three putative WGD events were identified within Parkerioideae, two of which were specific to Ceratopteris and Acrostichum, respectively. The functional enrichment analysis indicated that the lineage-specific WGD events have played a role in the adaptation of Parkerioideae to the low oxygen concentrations of aquatic habitats, as well as different aquatic environments of Ceratopteris and Acrostichum, such as the adaptation of Ceratopteris to reduced light levels and the adaptation of Acrostichum to high salinity. Positive selection analysis further provided evidence that the putative WGD events may have facilitated the adaptation of Parkerioideae to changes in habitat. Moreover, the gene family analysis indicated that the plasma membrane H+-ATPase (AHA), vacuolar H+-ATPase (VHA), and suppressor of K+ transport growth defect 1 (SKD1) may have been involved in the high salinity adaptation of Acrostichum. Our study provides new insights into the evolution and adaptations of Parkerioideae in different aquatic environments.

Angiosperm-wide analysis of fruit and ovary evolution aided by a new nuclear phylogeny supports association of the same ovary type with both dry and fleshy fruits

Fruit functions in seed protection and dispersal and belongs to many dry and fleshy types, yet their evolutionary pattern remains unclear in part due to uncertainties in the phylogenetic relationships among several orders and families. Thus we used nuclear genes of 502 angiosperm species representing 231 families to reconstruct a well supported phylogeny, with resolved relationships for orders and families with previously uncertain placements. Using this phylogeny as a framework, molecular dating supports a Triassic origin of the crown angiosperms, followed by the emergence of most orders in the Jurassic and Cretaceous and their rise to ecological dominance during the Cretaceous Terrestrial Revolution. The robust phylogeny allowed an examination of the evolutionary pattern of fruit and ovary types, revealing a trend of parallel carpel fusions during early diversifications in eudicots, monocots, and magnoliids. Moreover, taxa in the same order or family with the same ovary type can develop either dry or fleshy fruits with strong correlations between specific types of dry and fleshy fruits; such associations of ovary, dry and fleshy fruits define several ovary-fruit "modules" each found in multiple families. One of the frequent modules has an ovary containing multiple ovules, capsules and berries, and another with an ovary having one or two ovules, achenes (or other single-seeded dry fruits) and drupes. This new perspective of relationships among fruit types highlights the closeness of specific dry and fleshy fruit types, such as capsule and berry, that develop from the same ovary type and belong to the same module relative to dry and fleshy fruits of other modules (such as achenes and drupes). Further analyses of gene families containing known genes for ovary and fruit development identified phylogenetic nodes with multiple gene duplications, supporting a possible role of whole-genome duplications, in combination with climate changes and animal behaviors, in angiosperm fruit and ovary diversification.

High quality genomes produced from single MinION flow cells clarify polyploid and demographic histories of critically endangered Fraxinus (ash) species

With populations of threatened and endangered species declining worldwide, efforts are being made to generate high quality genomic records of these species before they are lost forever. Here, we demonstrate that data from single Oxford Nanopore Technologies (ONT) MinION flow cells can, even in the absence of highly accurate short DNA-read polishing, produce high quality de novo plant genome assemblies adequate for downstream analyses, such as synteny and ploidy evaluations, paleodemographic analyses, and phylogenomics. This study focuses on three North American ash tree species in the genus Fraxinus (Oleaceae) that were recently added to the International Union for Conservation of Nature (IUCN) Red List as critically endangered. Our results support a hexaploidy event at the base of the Oleaceae as well as a subsequent whole genome duplication shared by Syringa, Osmanthus, Olea, and Fraxinus. Finally, we demonstrate the use of ONT long-read sequencing data to reveal patterns in demographic history.

Draft genome assemblies for two species of Escallonia (Escalloniales)

OBJECTIVES

Escallonia (Escalloniaceae) belongs to the Escalloniales, a diverse clade of flowering plants with unclear placement in the tree of life. Escallonia species show impressive morphological and ecological diversity and are widely distributed across three hotspots of biodiversity in the Neotropics. To shed light on the genomic substrate of this radiation and the phylogenetic placement of Escalloniales as well as to generate useful data for comparative evolutionary genomics across flowering plants, we produced and annotated draft genomes for two species of Escallonia.

DATA DESCRIPTION

Genomic DNA from E. rubra and E. herrerae was sequenced with Oxford Nanopore sequencing chemistry, generating 3.4 and 12 million sequence reads with an average read length of 9.4 and 9.1 Kb (approximately 31 and 111 Gb of sequence data), respectively. In addition, we generated Illumina 100-bp paired-end short read data for E. rubra (approximately 75 Gb of sequence data). The Escallonia rubra genome was 566 Mb, with 3,233 contigs and an N50 of 285 Kb. The assembled genome for E. herrerae was 994 Mp, with 5,760 contigs and an N50 of 317 Kb. The genome sequences were annotated with 31,038 (E. rubra) and 47,905 (E. herrerea) protein-coding gene models supported by transcriptome/protein evidence and/or Pfam domain content. BUSCO assessments indicated completeness levels of approximately 98% for the genome assemblies and 88% for the genome annotations.

Novel Tri-Segmented Rhabdoviruses: A Data Mining Expedition Unveils the Cryptic Diversity of Cytorhabdoviruses

Cytorhabdoviruses (genus Cytorhabdovirus, family Rhabdoviridae) are plant-infecting viruses with enveloped, bacilliform virions. Established members of the genus Cytorhabdovirus have unsegmented single-stranded negative-sense RNA genomes (ca. 10-16 kb) which encode four to ten proteins. Here, by exploring large publicly available metatranscriptomics datasets, we report the identification and genomic characterization of 93 novel viruses with genetic and evolutionary cues of cytorhabdoviruses. Strikingly, five unprecedented viruses with tri-segmented genomes were also identified. This finding represents the first tri-segmented viruses in the family Rhabdoviridae, and they should be classified in a novel genus within this family for which we suggest the name "Trirhavirus". Interestingly, the nucleocapsid and polymerase were the only typical rhabdoviral proteins encoded by those tri-segmented viruses, whereas in three of them, a protein similar to the emaravirus (family Fimoviridae) silencing suppressor was found, while the other predicted proteins had no matches in any sequence databases. Genetic distance and evolutionary insights suggest that all these novel viruses may represent members of novel species. Phylogenetic analyses, of both novel and previously classified plant rhabdoviruses, provide compelling support for the division of the genus Cytorhabdovirus into three distinct genera. This proposed reclassification not only enhances our understanding of the evolutionary dynamics within this group of plant rhabdoviruses but also illuminates the remarkable genomic diversity they encompass. This study not only represents a significant expansion of the genomics of cytorhabdoviruses that will enable future research on the evolutionary peculiarity of this genus but also shows the plasticity in the rhabdovirus genome organization with the discovery of tri-segmented members with a unique evolutionary trajectory.

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.

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.

Phylotranscriptomic analyses reveal deep gene tree discordance in Camellia (Theaceae)

Gene tree discordance is a significant legacy of biological evolution. Multiple factors can result in incongruence among genes, such as introgression, incomplete lineage sorting (ILS), gene duplication or loss. Resolving the background of gene tree discordance is a critical way to uncover the process of species diversification. Camellia, the largest genus in Theaceae, has controversial taxonomy and systematics due in part to a complex evolutionary history. We used 60 transcriptomes of 55 species, which represented 15 sections of Camellia to investigate its phylogeny and the possible causes of gene tree discordance. We conducted gene tree discordance analysis based on 1,617 orthologous low-copy nuclear genes, primarily using coalescent species trees and polytomy tests to distinguish hard and soft conflict. A selective pressure analysis was also performed to assess the impact of selection on phylogenetic topology reconstruction. Our results detected different levels of gene tree discordance in the backbone of Camellia, and recovered rapid diversification as one of the possible causes of gene tree discordance. Furthermore, we confirmed that none of the currently proposed sections of Camellia was monophyletic. Comparisons among datasets partitioned under different selective pressure regimes showed that integrating all orthologous genes provided the best phylogenetic resolution of the species tree of Camellia. The findings of this study reveal rapid diversification as a major source of gene tree discordance in Camellia and will facilitate future investigation of reticulate relationships at the species level in this important plant genus.

Phylogenomic Analyses Reveal an Allopolyploid Origin of Core Didymocarpinae (Gesneriaceae) Followed by Rapid Radiation

Allopolyploid plants have long been regarded as possessing genetic advantages under certain circumstances due to the combined effects of their hybrid origins and duplicated genomes. However, the evolutionary consequences of allopolyploidy in lineage diversification remain to be fully understood. Here, we investigate the evolutionary consequences of allopolyploidy using 138 transcriptomic sequences of Gesneriaceae, including 124 newly sequenced, focusing particularly on the largest subtribe Didymocarpinae. We estimated the phylogeny of Gesneriaceae using concatenated and coalescent-based methods based on five different nuclear matrices and 27 plastid genes, focusing on relationships among major clades. To better understand the evolutionary affinities in this family, we applied a range of approaches to characterize the extent and cause of phylogenetic incongruence. We found that extensive conflicts between nuclear and chloroplast genomes and among nuclear genes were caused by both incomplete lineage sorting (ILS) and reticulation, and we found evidence of widespread ancient hybridization and introgression. Using the most highly supported phylogenomic framework, we revealed multiple bursts of gene duplication throughout the evolutionary history of Gesneriaceae. By incorporating molecular dating and analyses of diversification dynamics, our study shows that an ancient allopolyploidization event occurred around the Oligocene-Miocene boundary, which may have driven the rapid radiation of core Didymocarpinae.

Phylogenomic and syntenic data demonstrate complex evolutionary processes in early radiation of the rosids

Some of the most vexing problems of deep level relationship that remain in angiosperms involve the superrosids. The superrosid clade contains a quarter of all angiosperm species, with 18 orders in three subclades (Vitales, Saxifragales and core rosids) exhibiting remarkable morphological and ecological diversity. To help resolve deep-level relationships, we constructed a high-quality chromosome-level genome assembly for Tiarella polyphylla (Saxifragaceae) thus providing broader genomic representation of Saxifragales. Whole genome microsynteny analysis of superrosids showed that Saxifragales shared more synteny clusters with core rosids than Vitales, further supporting Saxifragales as more closely related with core rosids. To resolve the ordinal phylogeny of superrosids, we screened 122 single copy nuclear genes from genomes of 36 species, representing all 18 superrosid orders. Vitales were recovered as sister to all other superrosids (Saxifragales + core rosids). Our data suggest dramatic differences in relationships compared to earlier studies within core rosids. Fabids should be restricted to the nitrogen-fixing clade, while Picramniales, the Celastrales-Malpighiales (CM) clade, Huerteales, Oxalidales, Sapindales, Malvales and Brassicales formed an "expanded" malvid clade. The Celastrales-Oxalidales-Malpighiales (COM) clade (sensu APG IV) was not monophyletic. Crossosomatales, Geraniales, Myrtales and Zygophyllales did not belong to either of our well-supported malvids or fabids. There is strong discordance between nuclear and plastid phylogenetic hypotheses for superrosid relationships; we show that this is best explained by a combination of incomplete lineage sorting and ancient reticulation.

A high-quality Bougainvillea genome provides new insights into evolutionary history and pigment biosynthetic pathways in the Caryophyllales

Bougainvillea is a perennial ornamental shrub that is highly regarded in ornamental horticulture around the world. However, the absence of genome data limits our understanding of the pathways involved in bract coloration and breeding. Here, we report a chromosome-level assembly of the giga-genome of Bougainvillea × buttiana 'Mrs Butt', a cultivar thought to be the origin of many other Bougainvillea cultivars. The assembled genome is ~5 Gb with a scaffold N50 of 151 756 278 bp and contains 86 572 genes which have undergone recent whole-genome duplication. We confirmed that multiple rounds of whole-genome multiplication have occurred in the evolutionary history of the Caryophyllales, reconstructed the relationship in the Caryophyllales at whole genome level, and found discordance between species and gene trees as the result of complex introgression events. We investigated betalain and anthocyanin biosynthetic pathways and found instances of independent evolutionary innovations in the nine different Caryophyllales species. To explore the potential formation mechanism of diverse bract colors in Bougainvillea, we analyzed the genes involved in betalain and anthocyanin biosynthesis and found extremely low expression of ANS and DFR genes in all cultivars, which may limit anthocyanin biosynthesis. Our findings indicate that the expression pattern of the betalain biosynthetic pathway did not directly correlate with bract color, and a higher expression level in the betalain biosynthetic pathway is required for colored bracts. This improved understanding of the correlation between gene expression and bract color allows plant breeding outcomes to be predicted with greater certainty.

Chromosome-level genome assemblies from two sandalwood species provide insights into the evolution of the Santalales

Sandalwood is one of the most expensive woods in the world and is well known for its long-lasting and distinctive aroma. In our study, chromosome-level genome assemblies for two sandalwood species (Santalum album and Santalum yasi) were constructed by integrating NGS short reads, RNA-seq, and Hi-C libraries with PacBio HiFi long reads. The S. album and S. yasi genomes were both assembled into 10 pseudochromosomes with a length of 229.59 Mb and 232.64 Mb, containing 21,673 and 22,816 predicted genes and a repeat content of 28.93% and 29.54% of the total genomes, respectively. Further analyses resolved a Santalum-specific whole-genome triplication event after divergence from ancestors of the Santalales lineage Malania, yet due to dramatic differences in transposon content, the Santalum genomes were only one-sixth the size of the Malania oleifera genome. Examination of RNA-seq data revealed a suite of genes that are differentially expressed in haustoria and might be involved in host hemiparasite interactions. The two genomes presented here not only provide an important comparative dataset for studying genome evolution in early diverging eudicots and hemiparasitic plants but will also hasten the application of conservation genomics for a lineage of trees recovering from decades of overexploitation.

Phylogenomic analyses of Camellia support reticulate evolution among major clades

Camellia (Theaceae) is a morphologically highly diverse genus of flowering plants and includes many famous species with high economic value, and the phylogeny of this genus is not fully resolved. We used 95 transcriptomes from 87 Camellia species and identified 1481 low-copy genes to conduct a detailed analysis of the phylogeny of this genus according to various data-screening criteria. The results show that, very different from the two existing classification systems of Camellia, 87 species are grouped into 8 main clades and two independent species, and that all 8 clades except Clade 8 were strongly supported by almost all the coalescent or concatenated trees using different gene subsets. However, the relationships among these clades were weakly supported and different from analyses using different gene subsets; furthermore, they do not agree with the phylogeny from chloroplast genomes of Camellia. Additional analyses support reticulate evolution (probably resulting from introgression or hybridization) among some major Camellia lineages, providing explanation for extensive gene tree conflicts. Furthermore, we inferred that together with the formation of East Asian subtropical evergreen broad-leaved forests, Camellia underwent a radiative divergence of major clades at 23 ∼ 19 Ma in the late Miocene then had a subsequent species burst at 10 ∼ 5 Ma. Principal component and cluster analyses provides new insights into morphological changes underlying the evolution of Camellia and a reference to further clarify subgenus and sections of this genus. The comprehensive study here including a nuclear phylogeny and other analyses reveal the rapid evolutionary history of Camellia.

The phylogeny and global biogeography of Primulaceae based on high-throughput DNA sequence data

The angiosperm family Primulaceae is morphologically diverse and distributed nearly worldwide. However, phylogenetic uncertainty has obstructed the identification of major morphological and biogeographic transitions within the clade. We used target capture sequencing with the Angiosperms353 probes, taxon-sampling encompassing nearly all genera of the family, tree-based sequence curation, and multiple phylogenetic approaches to investigate the major clades of Primulaceae and their relationship to other Ericales. We generated dated phylogenetic trees and conducted broad-scale biogeographic analyses as well as stochastic character mapping of growth habit. We show that Ardisia, a pantropical genus and the largest in the family, is not monophyletic, with at least 19 smaller genera nested within it. Neotropical members of Ardisia and several smaller genera form a clade, an ancestor of which arrived in the Neotropics and began diversifying about 20 Ma. This Neotropical clade is most closely related to Elingamita and Tapeinosperma, which are most diverse on islands of the Pacific. Both Androsace and Primula are non-monophyletic by the inclusion of smaller genera. Ancestral state reconstructions revealed that there have either been parallel transitions to an herbaceous habit in Primuloideae, Samolus, and at least three lineages of Myrsinoideae, or a common ancestor of nearly all Primulaceae was herbaceous. Our results provide a robust estimate of phylogenetic relationships across Primulaceae and show that a revised classification of Myrsinoideae and several other clades within the family is necessary to render all genera monophyletic.

Deep reticulation: the long legacy of hybridization in vascular plant evolution

Hybridization has long been recognized as a fundamental evolutionary process in plants but, until recently, our understanding of its phylogenetic distribution and biological significance across deep evolutionary scales has been largely obscure. Over the past decade, genomic and phylogenomic datasets have revealed, perhaps not surprisingly, that hybridization, often associated with polyploidy, has been common throughout the evolutionary history of plants, particularly in various lineages of flowering plants. However, phylogenomic studies have also highlighted the challenges of disentangling signals of ancient hybridization from other sources of genomic conflict (in particular, incomplete lineage sorting). Here, we provide a critical review of ancient hybridization in vascular plants, outlining well-documented cases of ancient hybridization across plant phylogeny, as well as the challenges unique to documenting ancient versus recent hybridization. We provide a definition for ancient hybridization, which, to our knowledge, has not been explicitly attempted before. Further documenting the extent of deep reticulation in plants should remain an important research focus, especially because published examples likely represent the tip of the iceberg in terms of the total extent of ancient hybridization. However, future research should increasingly explore the macroevolutionary significance of this process, in terms of its impact on evolutionary trajectories (e.g. how does hybridization influence trait evolution or the generation of biodiversity over long time scales?), as well as how life history and ecological factors shape, or have shaped, the frequency of hybridization across geologic time and plant phylogeny. Finally, we consider the implications of ubiquitous ancient hybridization for how we conceptualize, analyze, and classify plant phylogeny. Networks, as opposed to bifurcating trees, represent more accurate representations of evolutionary history in many cases, although our ability to infer, visualize, and use networks for comparative analyses is highly limited. Developing improved methods for the generation, visualization, and use of networks represents a critical future direction for plant biology. Current classification systems also do not generally allow for the recognition of reticulate lineages, and our classifications themselves are largely based on evidence from the chloroplast genome. Updating plant classification to better reflect nuclear phylogenies, as well as considering whether and how to recognize hybridization in classification systems, will represent an important challenge for the plant systematics community.

Chromosomal-Scale Genome Assemblies of Two Coastal Plant Species, Scaevola taccada and S. hainanensis-Insight into Adaptation Outside of the Common Range

While most of the species in Goodeniaceae family, excluding the Scaevola genus, are endemic to Australasia, S. taccada and S. hainanensis have expanded their distribution range to the tropical coastlines of the Atlantic and Indian Oceans. S. taccada appears to be highly adapted to coastal sandy lands and cliffs, and it has become invasive in places. S. hainanensis is found mainly in salt marshes near mangrove forests, and is at risk of extinction. These two species provide a good system to investigate adaptive evolution outside the common distribution range of this taxonomic group. Here, we report their chromosomal-scale genome assemblies with the objective of probing their genomic mechanisms related to divergent adaptation after leaving Australasia. The scaffolds were assembled into eight chromosome-scale pseudomolecules, which covered 90.12% and 89.46% of the whole genome assembly for S. taccada and S. hainanensis, respectively. Interestingly, unlike many mangroves, neither species has undergone whole-genome duplication. We show that private genes, specifically copy-number expanded genes are essential for stress response, photosynthesis, and carbon fixation. The gene families that are expanded in S. hainanensis and contracted in S. taccada might have facilitated adaptation to high salinity in S. hainanensis. Moreover, the genes under positive selection in S. hainanensis have contributed to its response to stress and its tolerance of flooding and anoxic environments. In contrast, compared with S. hainanensis, the more drastic copy number expansion of FAR1 genes in S. taccada might have facilitated its adaptation to the stronger light radiation present in sandy coastal lands. In conclusion, our study of the chromosomal-scale genomes of S. taccada and S. hainanensis provides novel insights into their genomic evolution after leaving Australasia.

The use of Anchored Hybrid Enrichment data to resolve higher-level phylogenetic relationships: A proof-of-concept applied to Asterales (Eudicotyledoneae; Angiosperms)

Anchored Hybrid Enrichment (AHE) is a tool for capturing orthologous regions of the nuclear genome shared in low or single copy across lineages. Despite the increasing number of studies using this method, its usefulness to estimate relationships at deeper taxonomic levels in plants has not been fully explored. Here we present a proof of concept about the performance of nuclear loci obtained with AHE to infer phylogenetic relationships and explore the use of gene sampling schemes to estimate divergence times in Asterales. We recovered low-copy nuclear loci using the AHE method from herbarium material and silica-preserved samples. Maximum likelihood, Bayesian inference, and coalescence approaches were used to reconstruct phylogenomic relationships. Dating analyses were conducted under a multispecies coalescent approach by jointly inferring species tree and divergence times with random gene sampling schemes and multiple calibrations. We recovered 403 low-copy nuclear loci for 63 species representing nine out of eleven families of Asterales. Phylogenetic hypotheses were congruent among the applied methods and previously published results. Analyses with concatenated datasets were strongly supported, but coalescence-based analyses showed low support for the phylogenetic position of families Argophyllaceae and Alseuosmiaceae. Estimated family ages were congruent among gene sampling schemes, with the mean age for Asterales around 130 Myr. Our study documents the usefulness of AHE for resolving phylogenetic relationships at deep phylogenetic levels in Asterales. Observed phylogenetic inconsistencies were possibly due to the non-inclusion of families Phellinceae and Pentaphragmataceae. Random gene sampling schemes produced consistent age estimates with coalescence and species tree relaxed clock approaches.

Nuclear phylogeny and insights into whole-genome duplications and reproductive development of Solanaceae plants

Solanaceae, the nightshade family, have ∼2700 species, including the important crops potato and tomato, ornamentals, and medicinal plants. Several sequenced Solanaceae genomes show evidence for whole-genome duplication (WGD), providing an excellent opportunity to investigate WGD and its impacts. Here, we generated 93 transcriptomes/genomes and combined them with 87 public datasets, for a total of 180 Solanaceae species representing all four subfamilies and 14 of 15 tribes. Nearly 1700 nuclear genes from these transcriptomic/genomic datasets were used to reconstruct a highly resolved Solanaceae phylogenetic tree with six major clades. The Solanaceae tree supports four previously recognized subfamilies (Goetzeioideae, Cestroideae, Nicotianoideae, and Solanoideae) and the designation of three other subfamilies (Schizanthoideae, Schwenckioideae, and Petunioideae), with the placement of several previously unassigned genera. We placed a Solanaceae-specific whole-genome triplication (WGT1) at ∼81 million years ago (mya), before the divergence of Schizanthoideae from other Solanaceae subfamilies at ∼73 mya. In addition, we detected two gene duplication bursts (GDBs) supporting proposed WGD events and four other GDBs. An investigation of the evolutionary histories of homologs of carpel and fruit developmental genes in 14 gene (sub)families revealed that 21 gene clades have retained gene duplicates. These were likely generated by the Solanaceae WGT1 and may have promoted fleshy fruit development. This study presents a well-resolved Solanaceae phylogeny and a new perspective on retained gene duplicates and carpel/fruit development, providing an improved understanding of Solanaceae evolution.

A plastid phylogenomic framework for the palm family (Arecaceae)

BACKGROUND

Over the past decade, phylogenomics has greatly advanced our knowledge of angiosperm evolution. However, phylogenomic studies of large angiosperm families with complete species or genus-level sampling are still lacking. The palms, Arecaceae, are a large family with ca. 181 genera and 2600 species and are important components of tropical rainforests bearing great cultural and economic significance. Taxonomy and phylogeny of the family have been extensively investigated by a series of molecular phylogenetic studies in the last two decades. Nevertheless, some phylogenetic relationships within the family are not yet well-resolved, especially at the tribal and generic levels, with consequent impacts for downstream research.

RESULTS

Plastomes of 182 palm species representing 111 genera were newly sequenced. Combining these with previously published plastid DNA data, we were able to sample 98% of palm genera and conduct a plastid phylogenomic investigation of the family. Maximum likelihood analyses yielded a robustly supported phylogenetic hypothesis. Phylogenetic relationships among all five palm subfamilies and 28 tribes were well-resolved, and most inter-generic phylogenetic relationships were also resolved with strong support.

CONCLUSIONS

The inclusion of nearly complete generic-level sampling coupled with nearly complete plastid genomes strengthened our understanding of plastid-based relationships of the palms. This comprehensive plastid genome dataset complements a growing body of nuclear genomic data. Together, these datasets form a novel phylogenomic baseline for the palms and an increasingly robust framework for future comparative biological studies of this exceptionally important plant family.

Evolution of 101 Apocynaceae plastomes and phylogenetic implications

Apocynaceae are one of the ten species-richest angiosperm families. However, the backbone phylogeny of the family is yet less well supported, and the evolution of plastome structure has not been thoroughly studied for the whole family. Herein, a total of 101 complete plastomes including 35 newly sequenced, 24 reassembled from public raw data and the rest from the NCBI GenBank database, representing 26 of 27 tribes of Apocynaceae, were used for comparative plastome analysis. Phylogenetic analyses were conducted using a combined plastid data matrix of 77 protein-coding genes from 162 taxa, encompassing all tribes and 41 of 49 subtribes of Apocynaceae. Plastome lengths ranged from 150,897 bp in Apocynum venetum to 178,616 bp in Hoya exilis. Six types of boundaries between the inverted repeat (IR) regions and single copy (SC) regions were identified. Different sizes of IR expansion were found in three lineages, including Alyxieae, Ceropegieae and Marsdenieae, suggesting multiple expansion events of the IRs over the SC regions in Apocynaceae. The IR regions of Marsdenieae evolved in two ways: expansion towards the large single copy (LSC) region in Lygisma + Stephanotis + Ruehssia + Gymnema (Cosmopolitan clade), and expansion towards both LSC and small single copy (SSC) region in Dischidia-Hoya alliance and Marsdenia (Asia-Pacific clade). Six coding genes and five non-coding regions were identified as highly variable, including accD, ccsA-ndhD, clpP, matK, ndhF, ndhG-ndhI, trnG(GCC)-trnfM(CAU), trnH(GUG)-psbA, trnY(GUA)-trnE(UUC), ycf1, and ycf2. Maximum likelihood and Bayesian phylogenetic analyses resulted in nearly identical tree topologies and produced a well-resolved backbone comprising 15 consecutive dichotomies that subdivided Apocynaceae into 15 clades. The subfamily Periplocoideae were embedded in the Apocynoid grade and were sister to the Echiteae-Odontadenieae-Mesechiteae clade with high support values. Three tribes (Melodineae, Vinceae, and Willughbeieae), the subtribe Amphineuriinae, and four genera (Beaumontia, Ceropegia, Hoya, and Stephanotis) were not resolved as monophyletic. Our work sheds light on the backbone phylogenetic relationships in the family Apocynaceae and offers insights into the evolution of Apocynaceae plastomes using the most densely sampled plastome dataset to date.

Analyses of Cullin1 homologs reveal functional redundancy in S-RNase-based self-incompatibility and evolutionary relationships in eudicots

In Petunia (Solanaceae family), self-incompatibility (SI) is regulated by the polymorphic S-locus, which contains the pistil-specific S-RNase and multiple pollen-specific S-Locus F-box (SLF) genes. SLFs assemble into E3 ubiquitin ligase complexes known as Skp1-Cullin1-F-box complexes (SCFSLF). In pollen tubes, these complexes collectively mediate ubiquitination and degradation of all nonself S-RNases, but not self S-RNase, resulting in cross-compatible, but self-incompatible, pollination. Using Petunia inflata, we show that two pollen-expressed Cullin1 (CUL1) proteins, PiCUL1-P and PiCUL1-B, function redundantly in SI. This redundancy is lost in Petunia hybrida, not because of the inability of PhCUL1-B to interact with SSK1, but due to a reduction in the PhCUL1-B transcript level. This is possibly caused by the presence of a DNA transposon in the PhCUL1-B promoter region, which was inherited from Petunia axillaris, one of the parental species of Pe. hybrida. Phylogenetic and syntenic analyses of Cullin genes in various eudicots show that three Solanaceae-specific CUL1 genes share a common origin, with CUL1-P dedicated to S-RNase-related reproductive processes. However, CUL1-B is a dispersed duplicate of CUL1-P present only in Petunia, and not in the other species of the Solanaceae family examined. We suggest that the CUL1s involved (or potentially involved) in the SI response in eudicots share a common origin.

Phylotranscriptomics of Swertiinae (Gentianaceae) reveals that key floral traits are not phylogenetically correlated

Establishing how lineages with similar traits are phylogenetically related remains critical for understanding the origin of biodiversity on Earth. Floral traits in plants are widely used to explore phylogenetic relationships and to delineate taxonomic groups. The subtribe Swertiinae (Gentianaceae) comprises more than 350 species with high floral diversity ranging from rotate to tubular corollas and possessing diverse nectaries. Here we performed phylogenetic analysis of 60 species from all 15 genera of the subtribe Swertiinae sensu Ho and Liu, representing the range of floral diversity, using data from the nuclear and plastid genomes. Extensive topological conflicts were present between the nuclear and plastome trees. Three of the 15 genera represented by multiple species are polyphyletic in both trees. Key floral traits including corolla type, absence or presence of lobe scales, nectary type, nectary position, and stigma type are randomly distributed in the nuclear and plastome trees without phylogenetic correlation. We also revealed the likely ancient hybrid origin of one large clade comprising 10 genera with diverse floral traits. These results highlight the complex evolutionary history of this subtribe. The phylogenies constructed here provide a basic framework for further exploring the ecological and genetic mechanisms underlying both species diversification and floral diversity.

An updated phylogeny, biogeography, and PhyloCode-based classification of Cornaceae based on three sets of genomic data

PREMISE

A major goal of systematic biology is to uncover the evolutionary history of organisms and translate that knowledge into stable classification systems. Here, we integrate three sets of genome-wide data to resolve phylogenetic relationships in Cornaceae (containing only Cornus s.l.), reconstruct the biogeographic history of the clade, and provide a revised classification using the PhyloCode to stabilize names for this taxonomically controversial group.

METHODS

We conducted phylogenetic analyses using 312 single-copy nuclear genes and 70 plastid genes from Angiosperms353 Hyb-Seq, plus numerous loci from RAD-Seq. We integrated fossils using morphological data and produced a dated phylogeny for biogeographical analysis.

RESULTS

A well-resolved, strongly supported, comprehensive phylogeny was obtained. Biogeographic analyses support an origin and rapid diversification of Cornus into four morphologically distinct major clades in the Northern Hemisphere (with an eastern Asian ancestor) during the late Cretaceous. Dispersal into Africa from eastern Asia likely occurred along the Tethys Seaway during the Paleogene, whereas dispersal into South America likely occurred during the Neogene. Diversification within the northern hemisphere likely involved repeated independent colonization of new areas during the Paleogene and Neogene along the Bering Land Bridge, the North Atlantic Land Bridge, and the Tethys Seaway. Thirteen strongly supported clades were named following rules of the PhyloCode.

CONCLUSIONS

Our study provides an example of integrating genomic and morphological data to produce a robust, explicit species phylogeny that includes fossil taxa, which we translate into an updated classification scheme using the PhyloCode to stabilize names.

Phylogenomics and the flowering plant tree of life

The advances accelerated by next-generation sequencing and long-read sequencing technologies continue to provide an impetus for plant phylogenetic study. In the past decade, a large number of phylogenetic studies adopting hundreds to thousands of genes across a wealth of clades have emerged and ushered plant phylogenetics and evolution into a new era. In the meantime, a roadmap for researchers when making decisions across different approaches for their phylogenomic research design is imminent. This review focuses on the utility of genomic data (from organelle genomes, to both reduced representation sequencing and whole-genome sequencing) in phylogenetic and evolutionary investigations, describes the baseline methodology of experimental and analytical procedures, and summarizes recent progress in flowering plant phylogenomics at the ordinal, familial, tribal, and lower levels. We also discuss the challenges, such as the adverse impact on orthology inference and phylogenetic reconstruction raised from systematic errors, and underlying biological factors, such as whole-genome duplication, hybridization/introgression, and incomplete lineage sorting, together suggesting that a bifurcating tree may not be the best model for the tree of life. Finally, we discuss promising avenues for future plant phylogenomic studies.

Icacinaceae fossil provides evidence for a Cretaceous origin of the lamiids

Today the asterids comprise over 80,000 species of flowering plants; however, relatively little is known about the timing of their early diversification. This is particularly true for the diverse lamiid clade, which comprises half of asterid diversity. Here, a lamiid fossil fruit assigned to Icacinaceae from the Campanian of western North America provides important macrofossil evidence indicating that lamiids diverged at least 80 million years ago and sheds light on potential Cretaceous rainforest-like ecosystems.