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Parasitic plants have a heterotrophic lifestyle, in which they withdraw all or part of their nutrients from their host through the haustorium. Despite the release of many draft genomes of parasitic plants, the genome evolution related to the parasitism feature of facultative parasites remains largely unknown. In this study, we present a high‐quality chromosomal‐level genome assembly for the facultative parasite Pedicularis kansuensis (Orobanchaceae), which invades both legume and grass host species in degraded grasslands on the Qinghai‐Tibet Plateau. This species has the largest genome size compared with other parasitic species, and expansions of long terminal repeat retrotransposons accounting for 62.37% of the assembly greatly contributed to the genome size expansion of this species. A total of 42,782 genes were annotated, and the patterns of gene loss in P. kansuensis differed from other parasitic species. We also found many mobile mRNAs between P. kansuensis and one of its host species, but these mobile mRNAs could not compensate for the functional losses of missing genes in P. kansuensis. In addition, we identified nine horizontal gene transfer (HGT) events from rosids and monocots, as well as one single‐gene duplication events from HGT genes, which differ distinctly from that of other parasitic species. Furthermore, we found evidence for HGT through transferring genomic fragments from phylogenetically remote host species. Taken together, these findings provide genomic insights into the evolution of facultative parasites and broaden our understanding of the diversified genome evolution in parasitic plants and the molecular mechanisms of plant parasitism. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Angiosperms dominate the Earth's ecosystems and provide most of the basic necessities for human life. The major angiosperm clades comprise 64 orders, as recognized by the APG IV classification. However, the phylogenetic relationships of angiosperms remain unclear, as phylogenetic trees with different topologies have been reconstructed depending on the sequence datasets utilized, from targeted genes to transcriptomes. Here, we used currently available de novo genome data to reconstruct the phylogenies of 366 angiosperm species from 241 genera belonging to 97 families across 43 of the 64 orders based on orthologous genes from the nuclear, plastid, and mitochondrial genomes of the same species with compatible datasets. The phylogenetic relationships were largely consistent with previously constructed phylogenies based on sequence variations in each genome type. However, there were major inconsistencies in the phylogenetic relationships of the five Mesangiospermae lineages when different genomes were examined. We discuss ways to address these inconsistencies, which could ultimately lead to the reconstruction of a comprehensive angiosperm tree of life. The angiosperm phylogenies presented here provide a basic framework for further updates and comparisons. These phylogenies can also be used as guides to examine the evolutionary trajectories among the three genome types during lineage radiation. [ABSTRACT FROM AUTHOR]

Background: Two widely cultivated annual buckwheat crops, Fagopyrum esculentum and F. tataricum, differ from each other in both rutin concentration and reproductive system. However, the underlying genetic mechanisms remain poorly elucidated. Results: Here, we report the first haplotype-resolved chromosome-level genome assemblies of the two species. Two haplotype genomes of F. esculentum were assembled as 1.23 and 1.19 Gb with N50 = 9.8 and 12.4 Mb, respectively; the two haplotype genomes of F. tataricum were 453.7 and 446.2 Mb with N50 = 50 and 30 Mb, respectively. We further annotated protein-coding genes of each haplotype genome based on available gene sets and 48 newly sequenced transcriptomes. We found that more repetitive sequences, especially expansion of long terminal repeat retrotransposons (LTR-RTs), contributed to the large genome size of F. esculentum. Based on the well-annotated sequences, gene expressions, and luciferase experiments, we identified the sequence mutations of the promoter regions of two key genes that are likely to have greatly contributed to the high rutin concentration and selfing reproduction in F. tartaricum. Conclusions: Our results highlight the importance of high-quality genomes to identify genetic mutations underlying phenotypic differences between closely related species. F. tataricum may have been experienced stronger selection than F. esculentum through choosing these two non-coding alleles for the desired cultivation traits. These findings further suggest that genetic manipulation of the non-coding promoter regions could be widely employed for breeding buckwheat and other crops. [ABSTRACT FROM AUTHOR]

Background: Eudicots are the most diverse group of flowering plants that compromise five well-defined lineages: core eudicots, Ranunculales, Proteales, Trochodendrales, and Buxales. However, the phylogenetic relationships between these five lineages and their chromosomal evolutions remain unclear, and a lack of high-quality genome analyses for Buxales has hindered many efforts to address this knowledge gap. Results: Here, we present a high-quality chromosome-level genome of Buxus austro-yunnanensis (Buxales). Our phylogenomic analyses revealed that Buxales and Trochodendrales are genetically similar and classified as sisters. Additionally, both are sisters to the core eudicots, while Ranunculales was found to be the first lineage to diverge from these groups. Incomplete lineage sorting and hybridization were identified as the main contributors to phylogenetic discordance (34.33%) between the lineages. In fact, B. austro-yunnanensis underwent only one whole-genome duplication event, and collinear gene phylogeny analyses suggested that separate independent polyploidizations occurred in the five eudicot lineages. Using representative genomes from these five lineages, we reconstructed the ancestral eudicot karyotype (AEK) and generated a nearly gapless karyotype projection for each eudicot species. Within core eudicots, we recovered one common chromosome fusion event in asterids and malvids, respectively. Further, we also found that the previously reported fused AEKs in Aquilegia (Ranunculales) and Vitis (core eudicots) have different fusion positions, which indicates that these two species have different karyotype evolution histories. Conclusions: Based on our phylogenomic and karyotype evolution analyses, we revealed the likely relationships and evolutionary histories of early eudicots. Ultimately, our study expands genomic resources for early-diverging eudicots. [ABSTRACT FROM AUTHOR]

Understanding how populations diverge and new species arise is a central question in evolutionary biology. "Allopatric" divergence through geographical isolation is considered to be the commonest mechanism generating species biodiversity in mountain ecosystems. However, the underlying genomic dynamics, especially genomic islands of elevated divergence and genes that are highly diverged as a result of lineage‐specific selection, remain poorly understood. Stellera chamaejasme has a wide geographical range across the Qinghai–Tibet Plateau and northern China, making it a good model with which to explore genomic divergence during speciation in mountain ecosystems. We assembled a high‐quality, chromosome‐level genome for this species and resequenced the genomes of 24 populations across its major distribution. Our population genomic analyses recovered four distinct genetic lineages corresponding to geographical distributions with contrasting environments. However, we revealed continuous gene flow during the historical divergences of these four lineages. Interlineage hybrids and plastome introgressions were frequently found in regions of contact, which further increased gene flow between two contacting lineages in the recent past. The elevated divergences were highly heterogeneous across the genome and selection of ancestral polymorphisims and divergence hitchhiking contributed greatly to the formation of genomic islands. The highly diverged and lineage‐specific positively selected genes within and outside genomic islands were annotated to be mainly involved in local adaptation. Our results suggest that genomic divergence in S. chamaejasme is likely to have been triggered and maintained by local selection together with geographical isolation. [ABSTRACT FROM AUTHOR]

Most extant angiosperms belong to Mesangiospermae, which comprises eudicots, monocots, magnoliids, Chloranthales and Ceratophyllales. However, phylogenetic relationships between these five lineages remain unclear. Here, we report the high-quality genome of a member of the Chloranthales lineage (Chloranthus sessilifolius). We detect only one whole genome duplication within this species and find that polyploidization events in different Mesangiospermae lineage are mutually independent. We also find that the members of all floral development-related gene lineages are present in C. sessilifolius despite its extremely simplified flower. The AP1 and PI genes, however, show a weak floral tissue-specialized expression. Our phylogenomic analyses suggest that Chloranthales and magnoliids are sister groups, and both are together sister to the clade comprising Ceratophyllales and eudicots, while the monocot lineage is sister to all other Mesangiospermae. Our findings suggest that in addition to hybridization, incomplete lineage sorting may largely account for phylogenetic inconsistencies between the observed gene trees. Chloranthales remain the last lineage of core angiosperms that lacks a nuclear genome assembly. Here, the authors report the genome assembly of Chloranthus sesilifolius and show that both hybridization and incomplete lineage sorting may have contributed to the phylogenetic incongruities in the literature. [ABSTRACT FROM AUTHOR]

Sichuan pepper is a commonly used spice in Asian cuisine. Sanshools and wgx‐50/gx‐50 isolated from it have been shown to possess a wide spectrum of medicinal properties. Here we generated a chromosome‐level genome assembly of one Sichuan pepper species Zanthoxylumarmatum characterized by drought tolerance and apomixis. Analyses of functionally related genes suggested that increased gene copy number and expression level of drought‐tolerant genes might play an important role in improving drought tolerance of Z. armatum. Moreover, a gene encoding an RWP‐RK domain‐containing protein was shown to contribute to apomixis in Z. armatum, which was further characterized by overexpression in Arabidopsis thaliana. Furthermore, based on gene homology searching and co‐expression patterns of metabolite concentration and gene expressions, we identified a number of candidate genes involved in the biosynthesis of sanshools and wgx‐50/gx‐50. Taken together, our results yield valuable insights for understanding the evolution of apomixis, drought tolerance, and alkaloid biosynthesis in Z. armatum. [ABSTRACT FROM AUTHOR]

Structural variants (SVs) represent an important genetic resource for both natural and artificial selection. Here we present a chromosome-scale reference genome for domestic yak (Bos grunniens) that has longer contigs and scaffolds (N50 44.72 and 114.39 Mb, respectively) than reported for any other ruminant genome. We further obtained long-read resequencing data for 6 wild and 23 domestic yaks and constructed a genetic SV map of 372,220 SVs that covers the geographic range of the yaks. The majority of the SVs contains repetitive sequences and several are in or near genes. By comparing SVs in domestic and wild yaks, we identified genes that are predominantly related to the nervous system, behavior, immunity, and reproduction and may have been targeted by artificial selection during yak domestication. These findings provide new insights in the domestication of animals living at high altitude and highlight the importance of SVs in animal domestication. [ABSTRACT FROM AUTHOR]

Camptothecin and its derivatives are widely used for treating malignant tumors. Previous studies revealed only a limited number of candidate genes for camptothecin biosynthesis in Camptotheca acuminata, and it is still poorly understood how its biosynthesis of camptothecin has evolved. Here, we report a high-quality, chromosome-level C. acuminata genome assembly. We find that C. acuminata experiences an independent whole-genome duplication and numerous genes derive from it are related to camptothecin biosynthesis. Comparing with Catharanthus roseus, the loganic acid O-methyltransferase (LAMT) in C. acuminata fails to convert loganic acid into loganin. Instead, two secologanic acid synthases (SLASs) convert loganic acid to secologanic acid. The functional divergence of the LAMT gene and positive evolution of two SLAS genes, therefore, both contribute greatly to the camptothecin biosynthesis in C. acuminata. Our results emphasize the importance of high-quality genome assembly in identifying genetic changes in the evolutionary origin of a secondary metabolite. Camptothecin is a monoterpene indole alkaloid with anti-tumor activity. Here, the authors assemble the genome of the camptothecin producing plant Camptotheca acuminata and provide insights into the evolutionary origin of camptothecin biosynthesis by comparing to the vinblastine and vincristine biosynthetic pathway in Catharanthus roseus. [ABSTRACT FROM AUTHOR]

Tetracentron sinense and Trochodendron aralioides are two Tertiary relict species of large trees in the family Trochodendraceae with narrow distributions on the mainland and islands of eastern Asia. They belong to the order Trochodendrales, which is one of the four early‐diverged eudicot lineages. These two relict species provide a good system in which to examine genomic changes that occurred as they survived during repeated climatic oscillations in the Quaternary. We sequenced the genome of Te. sinense and compared it with that of Tr. aralioides. We found that Te. sinense has a smaller genome size (986.3 Mb) than that of Tr. aralioides (1610 Mb). Repetitive elements made the major contribution to the contrasting genome sizes in the two species, with most bursts of repeats occurring within the past four million years when the climate oscillated greatly. These species share two rounds of whole‐genome duplications. The mainland species Te. sinense had a larger effective population size than the island species Tr. aralioides after the largest glaciation during the Quaternary climatic oscillation. However, soon after this recovery stage, the effective population sizes of both species continued to decrease, although the current effective population size of Te. sinense is still larger than that of Tr. aralioides. We recovered three distinctly diverged clades through resequencing the genomes of 50 individuals across the distributional range of Te. sinense in China. Our results provide an important genomic resource with which to examine early trait evolution in the core eudicots and assist efforts to conserve this relict tree species. [ABSTRACT FROM AUTHOR]

Pervasive hybridization and whole-genome duplications (WGDs) influenced genome evolution in several eukaryotic lineages. Although frequent and recurrent hybridizations may result in reticulate phylogenies, the evolutionary events underlying these reticulations, including detailed structure of the ancestral diploid and polyploid genomes, were only rarely reconstructed. Here, we elucidate the complex genomic history of a monophyletic clade from the mustard family (Brassicaceae), showing contentious relationships to the early-diverging clades of this model plant family. Genome evolution in the crucifer tribe Biscutelleae (∼60 species, 5 genera) was dominated by pervasive hybridizations and subsequent genome duplications. Diversification of an ancestral diploid genome into several divergent but crossable genomes was followed by hybridizations between these genomes. Whereas a single genus (Megadenia) remained diploid, the four remaining genera originated by allopolyploidy (Biscutella , Lunaria , Ricotia) or autopolyploidy (Heldreichia). The contentious relationships among the Biscutelleae genera, and between the tribe and other early diverged crucifer lineages, are best explained by close genomic relatedness among the recurrently hybridizing ancestral genomes. By using complementary cytogenomics and phylogenomics approaches, we demonstrate that the origin of a monophyletic plant clade can be more complex than a parsimonious assumption of a single WGD spurring postpolyploid cladogenesis. Instead, recurrent hybridization among the same and/or closely related parental genomes may phylogenetically interlink diploid and polyploid genomes despite the incidence of multiple independent WGDs. Our results provide new insights into evolution of early-diverging Brassicaceae lineages and elucidate challenges in resolving the contentious relationships within and between land plant lineages with pervasive hybridization and WGDs. [ABSTRACT FROM AUTHOR]

Dioecy, the presence of separate sexes on distinct individuals, has evolved repeatedly in multiple plant lineages. However, the specific mechanisms by which sex systems evolve and their commonalities among plant species remain poorly understood. With both XY and ZW sex systems, the family Salicaceae provides a system to uncover the evolutionary forces driving sex chromosome turnovers. In this study, we performed a genome-wide association study to characterize sex determination in two Populus species, P. euphratica and P. alba. Our results reveal an XY system of sex determination on chromosome 14 of P. euphratica , and a ZW system on chromosome 19 of P. alba. We further assembled the corresponding sex-determination regions, and found that their sex chromosome turnovers may be driven by the repeated translocations of a Helitron -like transposon. During the translocation, this factor may have captured partial or intact sequences that are orthologous to a type-A cytokinin response regulator gene. Based on results from this and other recently published studies, we hypothesize that this gene may act as a master regulator of sex determination for the entire family. We propose a general model to explain how the XY and ZW sex systems in this family can be determined by the same RR gene. Our study provides new insights into the diversification of incipient sex chromosomes in flowering plants by showing how transposition and rearrangement of a single gene can control sex in both XY and ZW systems. [ABSTRACT FROM AUTHOR]

Megacarpaea delavayi (Brassicaceae), a plant found the high mountains of southwest China at high altitudes (3000–4800 m), is used as a vegetable or medicine. Here, we report a draft genome for this species. The assembly genome of M. delavayi is 883 Mb, and 61.59% of the genome is composed of repeat sequences. Annotation of the genome identified a total of 41,114 protein-coding genes. We found that M. delavayi experienced an independent whole-genome duplication (WGD), paralleling those independent WGDs in Iberis , Biscutella , and Anastatica in the early Miocene. Phylogenetic analyses based on the single-copy genes confirmed the position of the genus Megacarpaea within the expanded lineage II of the family and resolved its basal divergence to a subclade consisting of Anastatica, Iberis , and Biscutella. Species-specific and fast-evolving genes in M. delavayi are mainly involved in "DNA repair" and "response to UV-B radiation." These genetic changes may together help this species survive in high-altitude environments. The reference genome reported here provides a valuable resource for studying adaptation of this and other alpine plants to the high-altitude habitats. [ABSTRACT FROM AUTHOR]

SUMMARY: Species are becoming extinct at unprecedented rates as a consequence of human activity. Hence it is important to understand the evolutionary dynamics of species with already small population sizes. Populus ilicifolia is a vulnerable poplar species that is isolated from other poplar species and is uniquely adapted to the Tropics. It has a very limited size, reproduces partly clonally and is therefore an excellent case study for conservation genomics. We present here the first annotated draft genome of P. ilicifolia, characterize genome‐wide patterns of polymorphisms and compare those to other poplar species with larger natural ranges. P. ilicifolia experienced a more prolonged and severe decline of effective population size (Ne) and signs of genetic erosion than any other poplar species with which it was compared. At present, the species has the lowest genome‐wide genetic diversity, the highest abundance of long runs of homozygosity, high inbreeding levels as well as a high overall accumulation of deleterious variants. However, more effective purging of severely deleterious variants and adaptation to the Tropics may have contributed to its survival. Hence, in spite of its limited genetic variation, it is certainly worth pursuing the conservation efforts of this unique species. Significance Statement: Whole‐genome sequencing of Populus ilicifolia, a vulnerable and isolated poplar tree from the Tropics that can reproduce both sexually and asexually, was used to explore how population history and reproduction affected its genetic characteristics, genetic load, and its potential for tropical adaptation. [ABSTRACT FROM AUTHOR]

Summary: Phylogenetic analysis is complicated by interspecific gene flow and the presence of shared ancestral polymorphisms, particularly those maintained by balancing selection. In this study, we aimed to examine the prevalence of these factors during the diversification of Populus, a model tree genus in the Northern Hemisphere.We constructed phylogenetic trees of 29 Populus taxa using 80 individuals based on re‐sequenced genomes. Our species tree analyses recovered four main clades in the genus based on consensus nuclear phylogenies, but in conflict with the plastome phylogeny. A few interspecific relationships remained unresolved within the multiple‐species clade because of inconsistent gene trees. Our results indicated that gene flow has been widespread within each clade and also occurred among the four clades during their early divergence.We identified 45 candidate genes with ancient polymorphisms maintained by balancing selection. These genes were mainly associated with mating compatibility, growth and stress resistance.Both gene flow and selection‐mediated ancient polymorphisms are prevalent in the genus Populus. These are potentially important contributors to adaptive variation. Our results provide a framework for the diversification of model tree genus that will facilitate future comparative studies. [ABSTRACT FROM AUTHOR]

A letter to the editor is presented on a study conducted on common genome duplication in willow genome and poplar genome.

Actinidia chinensis (kiwifruit) is a perennial horticultural crop species of the Actinidiaceae family with high nutritional and economic value. Two versions of the A. chinensis genomes have been previously assembled, based mainly on relatively short reads. Here, we report an improved chromosome-level reference genome of A. chinensis (v3.0), based mainly on PacBio long reads and Hi-C data. The high-quality assembled genome is 653 Mb long, with 0.76% heterozygosity. At least 43% of the genome consists of repetitive sequences, and the most abundant long terminal repeats were further identified and account for 23.38% of our novel genome. It has clear improvements in contiguity, accuracy, and gene annotation over the two previous versions and contains 40,464 annotated protein-coding genes, of which 94.41% are functionally annotated. Moreover, further analyses of genetic collinearity revealed that the kiwifruit genome has undergone two whole-genome duplications: one affecting all Ericales families near the K-T extinction event and a recent genus-specific duplication. The reference genome presented here will be highly useful for further molecular elucidation of diverse traits and for the breeding of this horticultural crop, as well as evolutionary studies with related taxa. [ABSTRACT FROM AUTHOR]

Wood, which consists mainly of plant cell walls, is an extremely important resource in daily lives. Genes whose products participate in the processes of cell wall and wood formation are therefore major subjects of plant science research. The Wood-Formation Related Genes database (WFRGdb, http://me.lzu.edu.cn/woodformation/) serves as a data resource center for genes involved in wood formation. To create this database, we collected plant genome data published in other online databases and predicted all cell wall and wood formation related genes using BLAST and HMMER. To date, 47 gene families and 33 transcription factors from 57 genomes (28 herbaceous, 22 woody and 7 non-vascular plants) have been covered and more than 122,000 genes have been checked and recorded. To provide easy access to these data, we have developed several search methods, which make it easy to download targeted genes or groups of genes free of charge in FASTA format. Sequence and phylogenetic analyses are also available online. WFRGdb brings together cell wall and wood formation related genes from all available plant genomes, and provides an integrative platform for gene inquiry, downloading and analysis. This database will therefore be extremely useful for those who focuses on cell wall and wood research. [ABSTRACT FROM AUTHOR]