Evolution and biogeography of gymnosperms

Phylotranscriptomic and ecological analyses reveal the evolution and morphological adaptation of Abies

Coniferous forests are under severe threat of the rapid anthropogenic climate warming. Abies (firs), the fourth-largest conifer genus, is a keystone component of the boreal and temperate dark-coniferous forests and harbors a remarkably large number of relict taxa. However, the uncertainty of the phylogenetic and biogeographic history of Abies significantly impedes our prediction of future dynamics and efficient conservation of firs. In this study, using 1,533 nuclear genes generated from transcriptome sequencing and a complete sampling of all widely recognized species, we have successfully reconstructed a robust phylogeny of global firs, in which four clades are strongly supported and all intersectional relationships are resolved, although phylogenetic discordance caused mainly by incomplete lineage sorting and hybridization was detected. Molecular dating and ancestral area reconstruction suggest a Northern Hemisphere high-latitude origin of Abies during the Late Cretaceous, but all extant firs diversified during the Miocene to the Pleistocene, and multiple continental and intercontinental dispersals took place in response to the late Neogene climate cooling and orogenic movements. Notably, four critically endangered firs endemic to subtropical mountains of China, including A. beshanzuensis, A. ziyuanensis, A. fanjingshanensis and A. yuanbaoshanensis from east to west, have different origins and evolutionary histories. Moreover, three hotspots of species richness, including western North America, central Japan, and the Hengduan Mountains, were identified in Abies. Elevation and precipitation, particularly precipitation of the coldest quarter, are the most significant environmental factors driving the global distribution pattern of fir species diversity. Some morphological traits are evolutionarily constrained, and those linked to elevational variation (e.g., purple cone) and cold resistance (e.g., pubescent branch and resinous bud) may have contributed to the diversification of global firs. Our study sheds new light on the spatiotemporal evolution of global firs, which will be of great help to forest management and species conservation in a warming world.

Mycorrhizal symbiosis in Taxus: a review

Taxus, a genus of conifers known for its medicinal significance, faces various conservation challenges with several species classified under different threat categories by the IUCN. The overharvesting of bark and leaves for the well-known chemotherapy drug paclitaxel has resulted in its population decline. Exploring the mycorrhizal relationship in Taxus is of utmost importance, as mycorrhizal fungi play pivotal roles in nutrition, growth, and ecological resilience. Taxus predominantly associates with arbuscular mycorrhizal fungi (AM), and reports suggest ectomycorrhizal (EM) or dual mycorrhizal associations as well. This review consolidates existing literature on mycorrhizal associations in Taxus species, focusing on structural, physiological, and molecular aspects. AM associations are well-documented in Taxus, influencing plant physiology and propagation. Conversely, EM associations remain relatively understudied, with limited evidence suggesting their occurrence. The review highlights the importance of further research to elucidate dual mycorrhizal associations in Taxus, emphasizing the need for detailed structural and physiological examinations to understand their impact on growth and survival.

Deep learning for automated segmentation and counting of hypocotyl and cotyledon regions in mature Pinus radiata D. Don. somatic embryo images

In commercial forestry and large-scale plant propagation, the utilization of artificial intelligence techniques for automated somatic embryo analysis has emerged as a highly valuable tool. Notably, image segmentation plays a key role in the automated assessment of mature somatic embryos. However, to date, the application of Convolutional Neural Networks (CNNs) for segmentation of mature somatic embryos remains unexplored. In this study, we present a novel application of CNNs for delineating mature somatic conifer embryos from background and residual proliferating embryogenic tissue and differentiating various morphological regions within the embryos. A semantic segmentation CNN was trained to assign pixels to cotyledon, hypocotyl, and background regions, while an instance segmentation network was trained to detect individual cotyledons for automated counting. The main dataset comprised 275 high-resolution microscopic images of mature Pinus radiata somatic embryos, with 42 images reserved for testing and validation sets. The evaluation of different segmentation methods revealed that semantic segmentation achieved the highest performance averaged across classes, achieving F1 scores of 0.929 and 0.932, with IoU scores of 0.867 and 0.872 for the cotyledon and hypocotyl regions respectively. The instance segmentation approach demonstrated proficiency in accurate detection and counting of the number of cotyledons, as indicated by a mean squared error (MSE) of 0.79 and mean absolute error (MAE) of 0.60. The findings highlight the efficacy of neural network-based methods in accurately segmenting somatic embryos and delineating individual morphological parts, providing additional information compared to previous segmentation techniques. This opens avenues for further analysis, including quantification of morphological characteristics in each region, enabling the identification of features of desirable embryos in large-scale production systems. These advancements contribute to the improvement of automated somatic embryogenesis systems, facilitating efficient and reliable plant propagation for commercial forestry applications.

Wood of trees: Cellular structure, molecular formation, and genetic engineering

Wood is an invaluable asset to human society due to its renewable nature, making it suitable for both sustainable energy production and material manufacturing. Additionally, wood derived from forest trees plays a crucial role in sequestering a significant portion of the carbon dioxide fixed during photosynthesis by terrestrial plants. Nevertheless, with the expansion of the global population and ongoing industrialization, forest coverage has been substantially decreased, resulting in significant challenges for wood production and supply. Wood production practices have changed away from natural forests toward plantation forests. Thus, understanding the underlying genetic mechanisms of wood formation is the foundation for developing high-quality, fast-growing plantation trees. Breeding ideal forest trees for wood production using genetic technologies has attracted the interest of many. Tremendous studies have been carried out in recent years on the molecular, genetic, and cell-biological mechanisms of wood formation, and considerable progress and findings have been achieved. These studies and findings indicate enormous possibilities and prospects for tree improvement. This review will outline and assess the cellular and molecular mechanisms of wood formation, as well as studies on genetically improving forest trees, and address future development prospects.

United by Conflict: Convergent Signatures of Parental Conflict in Angiosperms and Placental Mammals

Endosperm in angiosperms and placenta in eutherians are convergent innovations for efficient embryonic nutrient transfer. Despite advantages, this reproductive strategy incurs metabolic costs that maternal parents disproportionately shoulder, leading to potential inter-parental conflict over optimal offspring investment. Genomic imprinting-parent-of-origin-biased gene expression-is fundamental for endosperm and placenta development and has convergently evolved in angiosperms and mammals, in part, to resolve parental conflict. Here, we review the mechanisms of genomic imprinting in these taxa. Despite differences in the timing and spatial extent of imprinting, these taxa exhibit remarkable convergence in the molecular machinery and genes governing imprinting. We then assess the role of parental conflict in shaping evolution within angiosperms and eutherians using four criteria: (1) Do differences in the extent of sibling relatedness cause differences in the inferred strength of parental conflict? (2) Do reciprocal crosses between taxa with different inferred histories of parental conflict exhibit parent-of-origin growth effects? (3) Are these parent-of-origin growth effects caused by dosage-sensitive mechanisms and do these loci exhibit signals of positive selection? (4) Can normal development be restored by genomic perturbations that restore stoichiometric balance in the endosperm/placenta? Although we find evidence for all criteria in angiosperms and eutherians, suggesting that parental conflict may help shape their evolution, many questions remain. Additionally, myriad differences between the two taxa suggest that their respective biologies may shape how/when/where/to what extent parental conflict manifests. Lastly, we discuss outstanding questions, highlighting the power of comparative work in quantifying the role of parental conflict in evolution.

A conserved graft formation process in Norway spruce and Arabidopsis identifies the PAT gene family as central regulators of wound healing

The widespread use of plant grafting enables eudicots and gymnosperms to join with closely related species and grow as one. Gymnosperms have dominated forests for over 200 million years, and despite their economic and ecological relevance, we know little about how they graft. Here we developed a micrografting method in conifers using young tissues that allowed efficient grafting with closely related species and between distantly related genera. Conifer graft junctions rapidly connected vasculature and differentially expressed thousands of genes including auxin and cell-wall-related genes. By comparing these genes to those induced during Arabidopsis thaliana graft formation, we found a common activation of cambium, cell division, phloem and xylem-related genes. A gene regulatory network analysis in Norway spruce (Picea abies) predicted that PHYTOCHROME A SIGNAL TRANSDUCTION 1 (PAT1) acted as a core regulator of graft healing. This gene was strongly up-regulated during both spruce and Arabidopsis grafting, and Arabidopsis mutants lacking PAT genes failed to attach tissues or successfully graft. Complementing Arabidopsis PAT mutants with the spruce PAT1 homolog rescued tissue attachment and enhanced callus formation. Together, our data show an ability for young tissues to graft with distantly related species and identifies the PAT gene family as conserved regulators of graft healing and tissue regeneration.

Diploid species phylogeny and evolutionary reticulation indicate early radiation of Ephedra in the Tethys coast

Reconstructing a robust species phylogeny and disentangling the evolutionary and biogeographic history of the gymnosperm genus Ephedra, which has a large genome and rich polyploids, remain a big challenge. Here we reconstructed a transcriptome-based phylogeny of 19 diploid Ephedra species, and explored evolutionary reticulations in this genus represented by 50 diploid and polyploid species, using four low-copy nuclear and nine plastid genes. The diploid species phylogeny indicates that the Mediterranean species diverged first, and the remaining species split into three clades, including the American species (Clade A), E. rhytidosperma, and all other Asian species (Clade B). The single-gene trees placed E. rhytidosperma sister to Clade A, Clade B, or Clades A + B in similar proportions, suggesting that radiation and gene flow likely occurred in the early evolution of Ephedra. In addition, reticulate evolution occurred not only among the deep nodes, but also in the recently evolved South American species, which further caused difficulty in phylogenetic reconstruction. Moreover, we found that allopolyploid speciation was pervasive in Ephedra. Our study also suggests that Ephedra very likely originated in the Tethys coast during the late Cretaceous, and the South American Ephedra species have a single origin by dispersal from Mexico or North America.

Epigenetic architecture of Pseudotaxus chienii: Revealing the synergistic effects of climate and soil variables

Whether conifers can withstand environmental changes especially temperature fluctuations has been controversial. Epigenetic analysis may provide new perspectives for solving the issue. Pseudotaxus chienii is an endangered gymnosperm species endemic to China. In this study, we have examined the genetic and epigenetic variations in its natural populations aiming to disentangle the synergistic effects of climate and soil on its population (epi)genetic differentiation by using amplified fragment length polymorphism (AFLP) and methylation-sensitive AFLP (MSAP) techniques. We identified 23 AFLP and 26, 7, and 5 MSAP outliers in P. chienii. Twenty-one of the putative adaptive AFLP loci were found associated with climate and/or soil variables including precipitation, temperature, K, Fe, Zn, and Cu, whereas 21, 7, and 4 MSAP outliers were significantly related to precipitation of wettest month (Bio13), precipitation driest of month (Bio14), percent tree cover (PTC), and soil Fe, Mn, and Cu compositions. Total precipitation and precipitation in the driest seasons were the most influential factors for genetic and epigenetic variation, respectively. In addition, a high full-methylation level and a strong correlation between genetic and epigenetic variation were detected in P. chienii. Climate is found of greater importance than soil in shaping adaptive (epi)genetic differentiation, and the synergistic effects of climate and climate-soil variables were also observed. The identified climate and soil variables should be considered when applying ex situ conservation.

Insights into the Ecological Diversification of the Hymenochaetales based on Comparative Genomics and Phylogenomics With an Emphasis on Coltricia

To elucidate the genomic traits of ecological diversification in the Hymenochaetales, we sequenced 15 new genomes, with attention to ectomycorrhizal (EcM) Coltricia species. Together with published data, 32 genomes, including 31 Hymenochaetales and one outgroup, were comparatively analyzed in total. Compared with those of parasitic and saprophytic members, EcM species have significantly reduced number of plant cell wall degrading enzyme genes, and expanded transposable elements, genome sizes, small secreted proteins, and secreted proteases. EcM species still retain some of secreted carbohydrate-active enzymes (CAZymes) and have lost the key secreted CAZymes to degrade lignin and cellulose, while possess a strong capacity to degrade a microbial cell wall containing chitin and peptidoglycan. There were no significant differences in secreted CAZymes between fungi growing on gymnosperms and angiosperms, suggesting that the secreted CAZymes in the Hymenochaetales evolved before differentiation of host trees into gymnosperms and angiosperms. Nevertheless, parasitic and saprophytic species of the Hymenochaetales are very similar in many genome features, which reflect their close phylogenetic relationships both being white rot fungi. Phylogenomic and molecular clock analyses showed that the EcM genus Coltricia formed a clade located at the base of the Hymenochaetaceae and divergence time later than saprophytic species. And Coltricia remains one to two genes of AA2 family. These indicate that the ancestors of Coltricia appear to have originated from saprophytic ancestor with the ability to cause a white rot. This study provides new genomic data for EcM species and insights into the ecological diversification within the Hymenochaetales based on comparative genomics and phylogenomics analyses.

Somatic Embryogenesis in Conifers: One Clade to Rule Them All?

Somatic embryogenesis (SE) in conifers is usually characterized as a multi-step process starting with the development of proembryogenic cell masses and followed by histodifferentiation, somatic embryo development, maturation, desiccation, and plant regeneration. Our current understanding of conifers' SE is mainly derived from studies using Pinaceae species as a model. However, the evolutionary relationships between conifers are not clear. Some hypotheses consider conifers as a paraphyletic group and Gnetales as a closely related clade. In this review, we used an integrated approach in order to cover the advances in knowledge on SE in conifers and Gnetales, discussing the state-of-the-art and shedding light on similarities and current bottlenecks. With this approach, we expect to be able to better understand the integration of these clades within current studies on SE. Finally, the points discussed raise an intriguing question: are non-Pinaceae conifers less prone to expressing embryogenic competence and generating somatic embryos as compared to Pinaceae species? The development of fundamental studies focused on this morphogenetic route in the coming years could be the key to finding a higher number of points in common between these species, allowing the success of the SE of one species to positively affect the success of another.

Wood cellulose microfibrils have a 24-chain core-shell nanostructure in seed plants

Wood cellulose microfibril (CMF) is the most abundant organic substance on Earth but its nanostructure remains poorly understood. There are controversies regarding the glucan chain number (N) of CMFs during initial synthesis and whether they become fused afterward. Here, we combined small-angle X-ray scattering, solid-state nuclear magnetic resonance and X-ray diffraction analyses to resolve CMF nanostructures in native wood. We developed small-angle X-ray scattering measurement methods for the cross-section aspect ratio and area of the crystalline-ordered CMF core, which has a higher scattering length density than the semidisordered shell zone. The 1:1 aspect ratio suggested that CMFs remain mostly segregated, not fused. The area measurement reflected the chain number in the core zone (Ncore). To measure the ratio of ordered cellulose over total cellulose (Roc) by solid-state nuclear magnetic resonance, we developed a method termed global iterative fitting of T1ρ-edited decay (GIFTED), in addition to the conventional proton spin relaxation editing method. Using the formula N = Ncore/Roc, most wood CMFs were found to contain 24 glucan chains, conserved between gymnosperm and angiosperm trees. The average CMF has a crystalline-ordered core of ~2.2 nm diameter and a semidisordered shell of ~0.5 nm thickness. In naturally and artificially aged wood, we observed only CMF aggregation (contact without crystalline continuity) but not fusion (forming a conjoined crystalline unit). This further argued against the existence of partially fused CMFs in new wood, overturning the recently proposed 18-chain fusion hypothesis. Our findings are important for advancing wood structural knowledge and more efficient use of wood resources in sustainable bio-economies.

Mitochondrial RNA editing sites affect the phylogenetic reconstruction of gymnosperms

•RNA editing sites may contain homoplasious signals that cause artifactual inferences in phylogenetic analyses.•Excluding RNA editing sites from gymnosperm mitochondrial genes restored the sister relationship of gnetophytes and Pinaceae.•Phylogenetic analysis based on mitochondrial genomic data should carefully evaluate the impact of RNA editing sites.

Insect pollination in deep time

Inferring insect pollination from compression fossils and amber inclusions is difficult because of a lack of consensus on defining an insect pollinator and the challenge of recognizing this ecological relationship in deep time. We propose a conceptual definition for such insects and an operational classification into pollinator or presumed pollinator. Using this approach, we identified 15 insect families that include fossil pollinators and show that pollination relationships have existed since at least the Upper Jurassic (~163 Ma). Insects prior to this can only be classified as presumed pollinators. This gives a more nuanced insight into the origin and evolution of an ecological relationship that is vital to the establishment, composition and conservation of modern terrestrial ecosystems.

Diversity, Distribution, Systematics and Conservation Status of Podocarpaceae

Among conifer families, Podocarpaceae is the second largest, with amazing diversity and functional traits, and it is the dominant Southern Hemisphere conifer family. However, comprehensive studies on diversity, distribution, systematic and ecophysiological aspects of the Podocarpaceae are sparse. We aim to outline and evaluate the current and past diversity, distribution, systematics, ecophysiological adaptations, endemism, and conservation status of podocarps. We analyzed data on the diversity and distribution of living and extinct macrofossil taxa and combined it with genetic data to reconstruct an updated phylogeny and understand historical biogeography. Podocarpaceae today contains 20 genera and approximately 219 taxa (201 species, 2 subspecies, 14 varieties and 2 hybrids) placed in three clades, plus a paraphyletic group/grade of four distinct genera. Macrofossil records show the presence of more than 100 podocarp taxa globally, dominantly from the Eocene-Miocene. Australasia (New Caledonia, Tasmania, New Zealand, and Malesia) is the hotspot of living podocarps diversity. Podocarps also show remarkable adaptations from broad to scale leaves, fleshy seed cones, animal dispersal, shrubs to large trees, from lowland to alpine regions and rheophyte to a parasite (including the only parasitic gymnosperm-Parasitaxus) and a complex pattern of seed and leaf functional trait evolution.

Five Species of Taxus Karyotype Based on Oligo-FISH for 5S rDNA and (AG3T3)3

As a relict plant, Taxus is used in a variety of medicinal ingredients, for instance to treat a variety of cancers. Taxus plants are difficult to distinguish from one another due to their similar morphology; indeed, some species of Taxus cytogenetic data still are unclear. Oligo-FISH can rapidly and efficiently provide insight into the genetic composition and karyotype. This is important for understanding the organization and evolution of chromosomes in Taxus species. We analysed five Taxus species using two oligonucleotide probes. (AG₃T₃)₃ signals were distributed at the chromosome ends and the centromere of five species of Taxus. The 5S rDNA signal was displayed on two chromosomes of five species of Taxus. In addition to Taxus wallichiana var. mairei, 5S rDNA signals were found proximal in the remaining four species, which signals a difference in its location. The karyotype formula of Taxus wallichiana was 2n = 2x = 24m, its karyotype asymmetry index was 55.56%, and its arm ratio was 3.0087. Taxus × media's karyotype formula was 2n = 2x = 24m, its karyotype asymmetry index was 55.09%, and its arm ratio was 3.4198. The karyotype formula of Taxus yunnanensis was 2n = 2x = 24m, its karyotype asymmetry index was 55.56%, and its arm ratio was 2.6402. The karyotype formula of Taxus cuspidate was 2n = 2x = 24m, its karyotype asymmetry index was 54.67%, its arm ratio was 3.0135, and two chromosomes exhibited the 5S rDNA signal. The karyotype formula of T. wallichiana var. mairei was 2n= 2x = 22m + 2sm, its karyotype asymmetry index was 54.33%, and its arm ratio was 2.8716. Our results provide the karyotype analysis and physical genetic map of five species of Taxus, which contributes to providing molecular cytogenetics data for Taxus.

Anatomical and biochemical evolutionary ancient traits of Araucaria araucana (Molina) K. Koch and their effects on carbon assimilation

The study of ancient species provides valuable information concerning the evolution of specific adaptations to past and current environmental conditions. Araucaria araucana (Molina) K. Koch belongs to one of the oldest families of conifers in the world, but despite this, there are few studies focused on its physiology and responses to changes in environmental conditions. We used an integrated approach aimed at comprehensively characterizing the ecophysiology of this poorly known species, focusing in its stomatal, mesophyll and biochemical traits, hypothesizing that these traits govern the carbon assimilation of A. araucana under past and present levels of atmospheric CO2. Results indicated that A. araucana presents the typical traits of an ancient species, such as large stomata and low stomatal density, which trigger low stomatal conductance and slow stomatal responsiveness to changing environmental conditions. Interestingly, the quantitative analysis showed that photosynthetic rates were equally limited by both diffusive and biochemical components. The Rubisco catalytic properties proved to have a low Rubisco affinity for CO2 and O2, similar to other ancient species. This affinity for CO2, together with the low carboxylation turnover rate, are responsible for the low Rubisco catalytic efficiency of carboxylation. These traits could be the result of the diverse environmental selective pressures that A. araucana was exposed during its diversification. The increase in measured temperatures induced an increase in stomatal and biochemical limitations, which together with a lower Rubisco affinity for CO2 could explain the low photosynthetic capacity of A. araucana in warmer conditions.

Plastome phylogenomics and biogeography of the subfam. Polygonoideae (Polygonaceae)

Polygonaceae has a complex taxonomic history, although a few studies using plastid or nuclear DNA fragments have explored relationships within this family, intrafamilial relationships remain controversial. Here, we newly sequenced and annotated 17 plastomes representing 12 genera within Polygonaceae. Combined with previously published data, a total of 49 plastomes representing 22/46 Polygonaceae genera and 16/20 Polygonoideae genera were collected to infer the phylogeny of Polygonaceae, with an emphasis on Polygonoideae. Plastome comparisons revealed high conservation within Polygonoideae in structure and gene order. Phylogenetic analyses using both Maximum Likelihood and Bayesian methods revealed two major clades and seven tribes within Polygonoideae. BEAST and S-DIVA analyses suggested a Paleocene origin of Polygonoideae in Asia. While most genera of Polygonoideae originated and further diversified in Asia, a few genera experienced multiple long-distance dispersal events from Eurasia to North America after the Miocene, with a few dispersal events to the Southern Hemisphere also being detected. Both ancient vicariance and long-distance events have played important roles in shaping the current distribution pattern of Polygonoideae.

Deep vicariance and frequent transoceanic dispersal shape the evolutionary history of a globally distributed fern family

PREMISE

The historical biogeography of ferns is typically expected to be dominated by long-distance dispersal due to their minuscule spores. However, few studies have inferred the historical biogeography of a large and widely distributed group of ferns to test this hypothesis. Our aims were to determine the extent to which long-distance dispersal vs. vicariance have shaped the history of the fern family Blechnaceae, to explore ecological correlates of dispersal and diversification, and to determine whether these patterns differ between the northern and southern hemispheres.

METHODS

We used sequence data for three chloroplast loci to infer a time-calibrated phylogeny for 154 of 265 species of Blechnaceae, including representatives of all genera in the family. This tree was used to conduct ancestral range reconstruction and stochastic character mapping, estimate diversification rates, and identify ecological correlates of diversification.

RESULTS

Blechnaceae originated in Eurasia and began diversifying in the late Cretaceous. A lineage comprising most extant diversity diversified principally in the austral Pacific region around the Paleocene-Eocene Thermal Maximum. Land connections that existed near the poles during periods of warm climates likely facilitated migration of several lineages, with subsequent climate-mediated vicariance shaping current distributions. Long-distance dispersal is frequent and asymmetrical, with New Zealand/Pacific Islands, Australia, and tropical America being major source areas.

CONCLUSIONS

Ancient vicariance and extensive long-distance dispersal have shaped the history of Blechnaceae in both the northern and southern hemispheres. The exceptional diversity in austral regions appears to reflect rapid speciation in these areas; mechanisms underlying this evolutionary success remain uncertain.

Correlations between leaf economics, mechanical resistance and drought tolerance across 41 cycad species

BACKGROUND AND AIMS

We conducted a comprehensive analysis of the functional traits of leaves (leaflets) of cycads. The aim of this study was to clarify the functional divergence between the earlier origin Cycadaceae and the later differentiated Zamiaceae, and the differences in trait associations between cycads and angiosperms.

METHODS

We selected 20 Cycadaceae species and 21 Zamiaceae species from the same cycad garden in South China, and measured their leaf structure, economic traits, mechanical resistance (Fp) and leaf water potential at the turgor loss point (πtlp). In addition, we compiled a dataset of geographical distribution along with climatic variables for these cycad species, and some leaf traits of tropical-sub-tropical angiosperm woody species from the literature for comparison.

KEY RESULTS

The results showed significantly contrasting leaf trait syndromes between the two families, with Zamiaceae species exhibiting thicker leaves, higher carbon investments and greater Fp than Cycadaceae species. Leaf thickness (LT) and πtlp were correlated with mean climatic variables in their native distribution ranges, indicating their evolutionary adaptation to environmental conditions. Compared with the leaves of angiosperms, the cycad leaves were thicker and tougher, and more tolerant to desiccation. Greater Fp was associated with a higher structural investment in both angiosperms and cycads; however, cycads showed lower Fp at a given leaf mass per area or LT than angiosperms. Enhancement of Fp led to more negative πtlp in angiosperms, but the opposite trend was observed in cycads.

CONCLUSIONS

Our results reveal that variations in leaf traits of cycads are mainly influenced by taxonomy and the environment of their native range. We also demonstrate similar leaf functional associations in terms of economics, but different relationships with regard to mechanics and drought tolerance between cycads and angiosperms. This study expands our understanding of the ecological strategies and likely responses of cycads to future climate change.

Conifer Biotechnology: An Overview

The peculiar characteristics of conifers determine the difficulty of their study and their great importance from various points of view. However, their study faces numerous important scientific, methodological, cultural, economic, social, and legal challenges. This paper presents an approach to several of those challenges and proposes a multidisciplinary scientific perspective that leads to a holistic understanding of conifers from the perspective of the latest technical, computer, and scientific advances. This review highlights the deep connection that all scientific contributions to conifers can have in each other as fully interrelated communicating vessels.

Recent advances on phylogenomics of gymnosperms and a new classification

Living gymnosperms comprise four major groups: cycads, Ginkgo, conifers, and gnetophytes. Relationships among/within these lineages have not been fully resolved. Next generation sequencing has made available a large number of sequences, including both plastomes and single-copy nuclear genes, for reconstruction of solid phylogenetic trees. Recent advances in gymnosperm phylogenomic studies have updated our knowledge of gymnosperm systematics. Here, we review major advances of gymnosperm phylogeny over the past 10 years and propose an updated classification of extant gymnosperms. This new classification includes three classes (Cycadopsida, Ginkgoopsida, and Pinopsida), five subclasses (Cycadidae, Ginkgoidae, Cupressidae, Pinidae, and Gnetidae), eight orders (Cycadales, Ginkgoales, Araucariales, Cupressales, Pinales, Ephedrales, Gnetales, and Welwitschiales), 13 families, and 86 genera. We also described six new tribes including Acmopyleae Y. Yang, Austrocedreae Y. Yang, Chamaecyparideae Y. Yang, Microcachrydeae Y. Yang, Papuacedreae Y. Yang, and Prumnopityeae Y. Yang, and made 27 new combinations in the genus Sabina.

An integrated high-resolution mapping shows congruent biodiversity patterns of Fagales and Pinales

The documentation of biodiversity distribution through species range identification is crucial for macroecology, biogeography, conservation, and restoration. However, for plants, species range maps remain scarce and often inaccurate. We present a novel approach to map species ranges at a global scale, integrating polygon mapping and species distribution modelling (SDM). We develop a polygon mapping algorithm by considering distances and nestedness of occurrences. We further apply an SDM approach considering multiple modelling algorithms, complexity levels, and pseudo-absence selections to map the species at a high spatial resolution and intersect it with the generated polygons. We use this approach to construct range maps for all 1957 species of Fagales and Pinales with data compilated from multiple sources. We construct high-resolution global species richness maps of these important plant clades, and document diversity hotspots for both clades in southern and south-western China, Central America, and Borneo. We validate the approach with two representative genera, Quercus and Pinus, using previously published coarser range maps, and find good agreement. By efficiently producing high-resolution range maps, our mapping approach offers a new tool in the field of macroecology for studying global species distribution patterns and supporting ongoing conservation efforts.

Repetitive Elements, Sequence Turnover and Cyto-Nuclear Gene Transfer in Gymnosperm Mitogenomes

Among the three genomes in plant cells, the mitochondrial genome (mitogenome) is the least studied due to complex recombination and intergenomic transfer. In gymnosperms only ∼20 mitogenomes have been released thus far, which hinders a systematic investigation into the tempo and mode of mitochondrial DNA evolution in seed plants. Here, we report the complete mitogenome sequence of Platycladus orientalis (Cupressaceae). This mitogenome is assembled as two circular-mapping chromosomes with a size of ∼2.6 Mb and which contains 32 protein-coding genes, three rRNA and seven tRNA genes, and 1,068 RNA editing sites. Repetitive sequences, including dispersed repeats, transposable elements (TEs), and tandem repeats, made up 23% of the genome. Comparative analyses with 17 other mitogenomes representing the five gymnosperm lineages revealed a 30-fold difference in genome size, 80-fold in repetitive content, and 230-fold in substitution rate. We found dispersed repeats are highly associated with mitogenome expansion (r = 0.99), and most of them were accumulated during recent duplication events. Syntenic blocks and shared sequences between mitogenomes decay rapidly with divergence time (r = 0.53), with the exceptions of Ginkgo and Cycads which retained conserved genome structure over long evolutionary time. Our phylogenetic analysis supports a sister group relationship of Cupressophytes and Gnetophytes; both groups are unique in that they lost 8–12 protein-coding genes, of which 4–7 intact genes are likely transferred to nucleus. These two clades also show accelerated and highly variable substitution rates relative to other gymnosperms. Our study highlights the dynamic and enigmatic evolution of gymnosperm mitogenomes.

Incomplete lineage sorting and local extinction shaped the complex evolutionary history of the Paleogene relict conifer genus, Chamaecyparis (Cupressaceae)

Inferring accurate biogeographic history of plant taxa with an East Asia (EA)-North America (NA) is usually hindered by conflicting phylogenies and a poor fossil record. The current distribution of Chamaecyparis (false cypress; Cupressaceae) with four species in EA, and one each in western and eastern NA, and its relatively rich fossil record, make it an excellent model for studying the EA-NA disjunction. Here we reconstruct phylogenomic relationships within Chamaecyparis using > 1400 homologous nuclear and 61 plastid genes. Our phylogenomic analyses using concatenated and coalescent approaches revealed strong cytonuclear discordance and conflicting topologies between nuclear gene trees. Incomplete lineage sorting (ILS) and hybridization are possible explanations of conflict; however, our coalescent analyses and simulations suggest that ILS is the major contributor to the observed phylogenetic discrepancies. Based on a well-resolved species tree and four fossil calibrations, the crown lineage of Chamaecyparis is estimated to have originated in the upper Cretaceous, followed by diversification events in the early and middle Paleogene. Ancestral area reconstructions suggest that Chamaecyparis had an ancestral range spanning both EA and NA. Fossil records further indicate that this genus is a relict of the "boreotropical" flora, and that local extinctions of European species were caused by global cooling. Overall, our results unravel a complex evolutionary history of a Paleogene relict conifer genus, which may have involved ILS, hybridization and the extinction of local species.

Host Shift Speciation of the Ectomycorrhizal Genus Suillus (Suillineae, Boletales) and Biogeographic Comparison With Its Host Pinaceae

Suillus is a genus of ectomycorrhizal fungi associated almost exclusively with Pinaceae. Lack of sample collections in East Asia and unresolved basal phylogenetic relationships of the genus are the major obstacles for better understanding the Suillus evolution. A resolved phylogeny of Suillus representing global diversity was achieved by sequencing multiple nuclear ribosomal and protein coding genes and extensive samples collected in East Asia. Fungal fossils are extremely rare, and the Eocene ectomycorrhizal symbiosis (ECM) fossil of Pinus root has been widely used for calibration. This study explored an alternative calibration scenario of the ECM fossil for controversy. Ancestral host associations of Suillus were estimated by maximum likelihood and Bayesian Markov chain Monte Carlo (MCMC) analyses, inferred from current host information from root tips and field observation. Host shift speciation explains the diversification of Suillus major clades. The three basal subgenera of Suillus were inferred to be associated with Larix, and diverged in early Eocene or Upper Cretaceous. In the early Oligocene or Paleocene, subgenus Suillus diverged and switched host to Pinus subgenus Strobus, and then switched to subgenus Pinus four times. Suillus subgenus Douglasii switched host from Larix to Pseudotsuga in Oligocene or Eocene. Increased species diversity occurred in subgenus Suillus after it switched host to Pinus but no associated speciation rate shifts were detected. Ancestral biogeographic distributions of Suillus and Pinaceae were estimated under the Dispersal Extinction Cladogenesis (DEC) model. Ancestral distribution patterns of Suillus and Pinaceae are related but generally discordant. Dispersals between Eurasia and North America explain the prevalence of disjunct Suillus taxa.

The dynamic history of gymnosperm plastomes: Insights from structural characterization, comparative analysis, phylogenomics, and time divergence

Gymnosperms are among the most endangered groups of plant species; they include ginkgo, pines (Conifers I), cupressophytes (Conifers II), cycads, and gnetophytes. The relationships among the five extant gymnosperm groups remain equivocal. We analyzed 167 available gymnosperm plastomes and investigated their diversity and phylogeny. We found that plastome size, structure, and gene order were highly variable in the five gymnosperm groups, of which Parasitaxus usta (Vieill.) de Laub. and Macrozamia mountperriensis F.M.Bailey had the smallest and largest plastomes, respectively. The inverted repeats (IRs) of the five groups were shown to have evolved through distinctive evolutionary scenarios. The IRs have been lost in all conifers but retained in cycads and gnetophytes. A positive association between simple sequence repeat (SSR) abundance and plastome size was observed, and the SSRs with the most variation were found in Pinaceae. Furthermore, the number of repeats was negatively correlated with IR length; thus, the highest number of repeats was detected in Conifers I and II, in which the IRs had been lost. We constructed a phylogeny based on 29 shared genes from 167 plastomes. With the plastome tree and 13 calibrations, we estimated the tree height between present-day angiosperms and gymnosperms to be ∼380 million years ago (mya). The placement of Gnetales in the tree agreed with the Gnetales-other gymnosperms hypothesis. The divergence between Ginkgo and cycads was estimated as ∼284 mya; the crown age of the cycads was 251 mya. Our time-calibrated plastid-based phylogenomic tree provides a framework for comparative studies of gymnosperm evolution.

Taxus yunnanensis genome offers insights into gymnosperm phylogeny and taxol production

Taxol, a natural product derived from Taxus, is one of the most effective natural anticancer drugs and the biosynthetic pathway of Taxol is the basis of heterologous bio-production. Here, we report a high-quality genome assembly and annotation of Taxus yunnanensis based on 10.7 Gb sequences assembled into 12 chromosomes with contig N50 and scaffold N50 of 2.89 Mb and 966.80 Mb, respectively. Phylogenomic analyses show that T. yunnanensis is most closely related to Sequoiadendron giganteum among the sampled taxa, with an estimated divergence time of 133.4-213.0 MYA. As with most gymnosperms, and unlike most angiosperms, there is no evidence of a recent whole-genome duplication in T. yunnanensis. Repetitive sequences, especially long terminal repeat retrotransposons, are prevalent in the T. yunnanensis genome, contributing to its large genome size. We further integrated genomic and transcriptomic data to unveil clusters of genes involved in Taxol synthesis, located on the chromosome 12, while gene families encoding hydroxylase in the Taxol pathway exhibited significant expansion. Our study contributes to the further elucidation of gymnosperm relationships and the Taxol biosynthetic pathway.

Evolution and structural variations in chloroplast tRNAs in gymnosperms

Background

Chloroplast transfer RNAs (tRNAs) can participate in various vital processes. Gymnosperms have important ecological and economic value, and they are the dominant species in forest ecosystems in the Northern Hemisphere. However, the evolution and structural changes in chloroplast tRNAs in gymnosperms remain largely unclear.

Results

In this study, we determined the nucleotide evolution, phylogenetic relationships, and structural variations in 1779 chloroplast tRNAs in gymnosperms. The numbers and types of tRNA genes present in the chloroplast genomes of different gymnosperms did not differ greatly, where the average number of tRNAs was 33 and the frequencies of occurrence for various types of tRNAs were generally consistent. Nearly half of the anticodons were absent. Molecular sequence variation analysis identified the conserved secondary structures of tRNAs. About a quarter of the tRNA genes were found to contain precoded 3′ CCA tails. A few tRNAs have undergone novel structural changes that are closely related to their minimum free energy, and these structural changes affect the stability of the tRNAs. Phylogenetic analysis showed that tRNAs have evolved from multiple common ancestors. The transition rate was higher than the transversion rate in gymnosperm chloroplast tRNAs. More loss events than duplication events have occurred in gymnosperm chloroplast tRNAs during their evolutionary process.

Conclusions

These findings provide novel insights into the molecular evolution and biological characteristics of chloroplast tRNAs in gymnosperms.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-08058-3.

Seeing through the hedge: Phylogenomics of Thuja (Cupressaceae) reveals prominent incomplete lineage sorting and ancient introgression for Tertiary relict flora

The Eastern Asia (EA) - North America (NA) disjunction is a well-known biogeographic pattern of the Tertiary relict flora; however, few studies have investigated the evolutionary history of this disjunction using a phylogenomic approach. Here, we used 2369 single copy nuclear genes and nearly full plastomes to reconstruct the evolutionary history of the small Tertiary relict genus Thuja, which consists of five disjunctly distributed species. The nuclear species tree strongly supported an EA clade Thuja standishii-Thuja sutchuenensis and a "disjunct clade", where western NA species T. plicata is sister to an EA-eastern NA disjunct Thuja occidentalis-Thuja koraiensis group. Our results suggested that the observed topological discordance among the gene trees as well as the cytonuclear discordance is mainly due to incomplete lineage sorting, probably facilitated by the fast diversification of Thuja around the Early Miocene and the large effective population sizes of ancestral lineages. Furthermore, approximately 20% of the T. sutchuenensis nuclear genome is derived from an unknown ancestral lineage of Thuja, which might explain the close resemblance of its cone morphology to that of an ancient fossil species. Overall, our study demonstrates that single genes may not resolve interspecific relationships for disjunct taxa, and that more reliable results will come from hundreds or thousands of loci, revealing a more complex evolutionary history. This will steadily improve our understanding of their origin and evolution.

Both Conifer II and Gnetales are characterized by a high frequency of ancient mitochondrial gene transfer to the nuclear genome

BACKGROUND

Mitochondrial gene transfer/loss is common in land plants, and therefore the fate of missing mitochondrial genes has attracted more and more attention. The gene content of gymnosperm mitochondria varies greatly, supplying a system for studying the evolutionary fate of missing mitochondrial genes.

RESULTS

Here, we studied the tempo and pattern of mitochondrial gene transfer/loss in gymnosperms represented by all 13 families, using high-throughput sequencing of both DNA and cDNA. All 41 mitochondrial protein-coding genes were found in cycads, Ginkgo and Pinaceae, whereas multiple mitochondrial genes were absent in Conifer II and Gnetales. In Conifer II, gene transfer from mitochondria to the nucleus followed by loss of the mitochondrial copy was common, but complete loss of a gene in both mitochondrial and nuclear genomes was rare. In contrast, both gene transfer and loss were commonly found in Gnetales. Notably, in Conifer II and Gnetales, the same five mitochondrial genes were transferred to the nuclear genome, and these gene transfer events occurred, respectively, in ancestors of the two lineages. A two-step transfer mechanism (retroprocessing and subsequent DNA-mediated gene transfer) may be responsible for mitochondrial gene transfer in Conifer II and Gnetales. Moreover, the mitochondrial gene content variation is correlated with gene length, GC content, hydrophobicity, and nucleotide substitution rates in land plants.

CONCLUSIONS

This study reveals a complete evolutionary scenario for variations of mitochondrial gene transferring in gymnosperms, and the factors responsible for mitochondrial gene content variation in land plants.

The complete mitochondrial genome of Cycas debaoensis revealed unexpected static evolution in gymnosperm species

Mitochondrial genomes of vascular plants are well known for their liability in architecture evolution. However, the evolutionary features of mitogenomes at intra-generic level are seldom studied in vascular plants, especially among gymnosperms. Here we present the complete mitogenome of Cycas debaoensis, an endemic cycad species to the Guangxi region in southern China. In addition to assemblage of draft mitochondrial genome, we test the conservation of gene content and mitogenomic stability by comparing it to the previously published mitogenome of Cycas taitungensis. Furthermore, we explored the factors such as structural rearrangements and nuclear surveillance of double-strand break repair (DSBR) proteins in Cycas in comparison to other vascular plant groups. The C. debaoensis mitogenome is 413,715 bp in size and encodes 69 unique genes, including 40 protein coding genes, 26 tRNAs, and 3 rRNA genes, similar to that of C. taitungensis. Cycas mitogenomes maintained the ancestral intron content of seed plants (26 introns), which is reduced in other lineages of gymnosperms, such as Ginkgo biloba, Taxus cuspidata and Welwitschia mirabilis due to selective pressure or retroprocessing events. C. debaoensis mitogenome holds 1,569 repeated sequences (> 50 bp), which partially account for fairly large intron size (1200 bp in average) of Cycas mitogenome. The comparison of RNA-editing sites revealed 267 shared non-silent editing site among predicted vs. empirically observed editing events. Another 33 silent editing sites from empirical data increase the total number of editing sites in Cycas debaoensis mitochondrial protein coding genes to 300. Our study revealed unexpected conserved evolution between the two Cycas species. Furthermore, we found strict collinearity of the gene order along with the identical set of genomic content in Cycas mt genomes. The stability of Cycas mt genomes is surprising despite the existence of large number of repeats. This structural stability may be related to the relative expansion of three DSBR protein families (i.e., RecA, OSB, and RecG) in Cycas nuclear genome, which inhibit the homologous recombinations, by monitoring the accuracy of mitochondrial chromosome repair.

Biological Nanofactories: Using Living Forms for Metal Nanoparticle Synthesis

Metal nanoparticles are nanosized entities with dimensions of 1-100 nm that are increasingly in demand due to applications in diverse fields like electronics, sensing, environmental remediation, oil recovery and drug delivery. Metal nanoparticles possess large surface energy and properties different from bulk materials due to their small size, large surface area with free dangling bonds and higher reactivity. High cost and pernicious effects associated with the chemical and physical methods of nanoparticle synthesis are gradually paving the way for biological methods due to their eco-friendly nature. Considering the vast potentiality of microbes and plants as sources, biological synthesis can serve as a green technique for the synthesis of nanoparticles as an alternative to conventional methods. A number of reviews are available on green synthesis of nanoparticles but few have focused on covering the entire biological agents in this process. Therefore present paper describes the use of various living organisms like bacteria, fungi, algae, bryophytes and tracheophytes in the biological synthesis of metal nanoparticles, the mechanisms involved and the advantages associated therein.

Wood transcriptome analysis of Pinus densiflora identifies genes critical for secondary cell wall formation and NAC transcription factors involved in tracheid formation

Although conifers have significant ecological and economic value, information on transcriptional regulation of wood formation in conifers is still limited. Here, to gain insight into secondary cell wall (SCW) biosynthesis and tracheid formation in conifers, we performed wood tissue-specific transcriptome analyses of Pinus densiflora (Korean red pine) using RNA sequencing. In addition, to obtain full-length transcriptome information, PacBio single molecule real-time iso-sequencing was carried out using RNAs from 28 tissues of P. densiflora. Subsequent comparative tissue-specific transcriptome analysis successfully pinpointed critical genes encoding key proteins involved in biosynthesis of the major secondary wall components (cellulose, galactoglucomannan, xylan and lignin). Furthermore, we predicted a total of 62 NAC (NAM, ATAF1/2 and CUC2) family transcription factor members and identified seven PdeNAC genes preferentially expressed in developing xylem tissues in P. densiflora. Protoplast-based transcriptional activation analysis found that four PdeNAC genes, homologous to VND, NST and SND/ANAC075, upregulated GUS activity driven by an SCW-specific cellulose synthase promoter. Consistently, transient overexpression of the four PdeNACs induced xylem vessel cell-like SCW deposition in both tobacco (Nicotiana benthamiana) and Arabidopsis leaves. Taken together, our data provide a foundation for further research to unravel transcriptional regulation of wood formation in conifers, especially SCW formation and tracheid differentiation.

Pollen Germination and Pollen Tube Growth in Gymnosperms

Pollen germination and pollen tube growth are common to all seed plants, but these processes first developed in gymnosperms and still serve for their successful sexual reproduction. The main body of data on the reproductive physiology, however, was obtained on flowering plants, and one should be careful to extrapolate the discovered patterns to gymnosperms. In recent years, physiological studies of coniferous pollen have been increasing, and both the features of this group and the similarities with flowering plants have already been identified. The main part of the review is devoted to physiological studies carried out on conifer pollen. The main properties and diversity of pollen grains and pollination strategies in gymnosperms are described.

Arabinogalactan-proteins from non-coniferous gymnosperms have unusual structural features

Arabinogalactan-proteins (AGPs), important signalling molecules of the plant cell wall, are structurally extensively investigated in angiosperms, but information on AGPs in gymnosperms is still limited. We characterized AGPs from the gymnosperms Ginkgo biloba, Ephedra distachya, Encephalartos longifolius and Cycas revoluta. The protein contents are comparable to that of angiosperm AGPs. Hydroxyproline is the site of linking the carbohydrate part and was detected in all AGPs with highest concentration in Cycas AGP (1.1 % of the AGP). Interestingly, with the exception of Cycas, all AGPs contained the monosaccharide 3-O-methylrhamnose not present in angiosperm polysaccharides. The carbohydrate moieties of Cycas and Ephredra showed the main components 1,3,6-linked galactose and terminal arabinose typical of angiosperm AGPs, whereas that of Ginkgo AGP was unique with 1,4-linked galactose as dominant structural element. Bioinformatic search for glycosyltransferases in Ginkgo genome also revealed a lower number of galactosyltransferases responsible for biosynthesis of the 1,3-Gal/1,6-Gal AGP backbone.

Phylogenomic and ecological analyses reveal the spatiotemporal evolution of global pines

How coniferous forests evolved in the Northern Hemisphere remains largely unknown. Unlike most groups of organisms that generally follow a latitudinal diversity gradient, most conifer species in the Northern Hemisphere are distributed in mountainous areas at middle latitudes. It is of great interest to know whether the midlatitude region has been an evolutionary cradle or museum for conifers and how evolutionary and ecological factors have driven their spatiotemporal evolution. Here, we investigated the macroevolution of Pinus, the largest conifer genus and characteristic of northern temperate coniferous forests, based on nearly complete species sampling. Using 1,662 genes from transcriptome sequences, we reconstructed a robust species phylogeny and reestimated divergence times of global pines. We found that ∼90% of extant pine species originated in the Miocene in sharp contrast to the ancient origin of Pinus, indicating a Neogene rediversification. Surprisingly, species at middle latitudes are much older than those at other latitudes. This finding, coupled with net diversification rate analysis, indicates that the midlatitude region has provided an evolutionary museum for global pines. Analyses of 31 environmental variables, together with a comparison of evolutionary rates of niche and phenotypic traits with a net diversification rate, found that topography played a primary role in pine diversification, and the aridity index was decisive for the niche rate shift. Moreover, fire has forced diversification and adaptive evolution of Pinus Our study highlights the importance of integrating phylogenomic and ecological approaches to address evolution of biological groups at the global scale.

Molecular evolution and SSRs analysis based on the chloroplast genome of Callitropsis funebris

Chloroplast genome sequences have been used to understand evolutionary events and to infer efficiently phylogenetic relationships. Callitropsis funebris (Cupressaceae) is an endemic species in China. Its phylogenetic position is controversial due to morphological characters similar to those of Cupressus, Callitropsis, and Chamaecyparis. This study used next-generation sequencing technology to sequence the complete chloroplast genome of Ca. funebris and then constructed the phylogenetic relationship between Ca. funebris and its related species based on a variety of data sets and methods. Simple sequence repeats (SSRs) and adaptive evolution analysis were also conducted. Our results showed that the monophyletic branch consisting of Ca. funebris and Cupressus tonkinensis is a sister to Cupressus, while Callitropsis is not monophyletic; Ca. nootkatensis and Ca. vietnamensis are nested in turn at the base of the monophyletic group Hesperocyparis. The statistical results of SSRs supported the closest relationship between Ca. funebris and Cupressus. By performing adaptive evolution analysis under the phylogenetic background of Cupressales, the Branch model detected three genes and the Site model detected 10 genes under positive selection; and the Branch-Site model uncovered that rpoA has experienced positive selection in the Ca. funebries branch. Molecular analysis from the chloroplast genome highly supported that Ca. funebris is at the base of Cupressus. Of note, SSR features were found to be able to shed some light on phylogenetic relationships. In short, this chloroplast genomic study has provided new insights into the phylogeny of Ca. funebris and revealed multiple chloroplast genes possibly undergoing adaptive evolution.

Brassinosteroids synthesised by CYP85A/A1 but not CYP85A2 function via a BRI1-like receptor but not via BRI1 in Picea abies

Brassinosteroids (BRs) are essential plant hormones. In angiosperms, brassinolide and castasterone, the first and second most active BRs, respectively, are synthesised by CYP85A2 and CYP85A/A1, respectively. BRs in angiosperms function through an essential receptor, BR Insensitive 1 (BRI1). In addition, some angiosperms also have non-essential BRI1-like 1/3 (BRL1/3). In conifers, BRs promote seed germination under drought stress; however, how BRs function in gymnosperms is unknown. In this study, we performed functional complementation of BR biosynthesis and receptor genes from Picea abies with respective Arabidopsis mutants. We found that P. abies possessed functional PaCYP85A and PaBRL1 but not PaCYP85A2 or PaBRI1, and this results in weak BR signaling, and both PaCYP85A and PaBRL1 were abundantly expressed. However, neither BR treatment of P. abies seedlings nor expression of PaBRL1 in the Arabidopsis Atbri1 mutant promoted plant height, despite the fact that BR-responsive genes were activated. Importantly, chimeric AtBRI1 replaced with the BR-binding domain of PaBRL1 complemented the Atbri1 phenotypes. Furthermore, PaBRL1 had less kinase activity than BRI1 in vitro. Overall, P. abies had weak but still active BR signaling, explaining aspects of its slow growth and high stress tolerance. Our study sheds light on the functional and evolutionary significance of distinct BR signaling that is independent of BRI1 and brassinolide.

Phylotranscriptomics reveals the complex evolutionary and biogeographic history of the genus Tsuga with an East Asian-North American disjunct distribution

The disjunct distribution between East Asia and North America is one of the best established biogeographic patterns. A robust phylogeny is fundamental for understanding the biogeographic histories of taxa with this distribution pattern. Tsuga (hemlock) is a genus of Pinaceae with a typical intercontinental disjunct distribution in East Asia and eastern and western North America, and its phylogeny has not been completely reconstructed in previous studies. In this study, we reconstructed a highly resolved phylogeny of Tsuga using 881 nuclear genes, 60 chloroplast genes and 23 mitochondrial genes and explored its biogeographic and reticulate evolutionary history. The results of phylogenetic analysis, molecular dating and ancestral area reconstruction indicate that Tsuga very likely originated from North America in the late Oligocene and dispersed from America to East Asia via the Bering Land Bridge during the middle Miocene. In particular, we found complex reticulate evolutionary pattern among the East Asian hemlock species. T. sieboldii possibly originated from hybridization with the ancestor of T. chinensis from mainland China and T. forrestii as the paternal donor and the ancestor of T. diversifolia and T. ulleungensis as the maternal donor. T. chinensis (Taiwan) could have originated by hybridization together with T. sieboldii and then evolved independently after dispersal to the Taiwan Island, subsequently experiencing mitochondrial DNA introgression with T. chinensis from mainland China. Moreover, our study found that T. chinensis from western China is more closely related to T. forrestii than to T. chinensis from eastern China. The nonmonophyletic T. chinensis needs taxonomic reconsideration.

Evolutionary analysis of chloroplast tRNA of Gymnosperm revealed the novel structural variation and evolutionary aspect

Gymnosperms such as ginkgo, conifers, cycads, and gnetophytes are vital components of land ecosystems, and they have significant economic and ecologic value, as well as important roles as forest vegetation. In this study, we investigated the structural variation and evolution of chloroplast transfer RNAs (tRNAs) in gymnosperms. Chloroplasts are important organelles in photosynthetic plants. tRNAs are key participants in translation where they act as adapter molecules between the information level of nucleic acids and functional level of proteins. The basic structures of gymnosperm chloroplast tRNAs were found to have family-specific conserved sequences. The tRNAΨ -loop was observed to contain a conforming sequence, i.e., U-U-C-N-A-N2. In gymnosperms, tRNAIle was found to encode a "CAU" anticodon, which is usually encoded by tRNAMet. Phylogenetic analysis suggested that plastid tRNAs have a common polyphyletic evolutionary pattern, i.e., rooted in abundant common ancestors. Analyses of duplication and loss events in chloroplast tRNAs showed that gymnosperm tRNAs have experienced little more gene loss than gene duplication. Transition and transversion analysis showed that the tRNAs are iso-acceptor specific and they have experienced unequal evolutionary rates. These results provide new insights into the structural variation and evolution of gymnosperm chloroplast tRNAs, which may improve our comprehensive understanding of the biological characteristics of the tRNA family.

Genome-wide RAD sequencing resolves the evolutionary history of serrate leaf Juniperus and reveals discordance with chloroplast phylogeny

Juniper (Juniperus) is an ecologically important conifer genus of the Northern Hemisphere, the members of which are often foundational tree species of arid regions. The serrate leaf margin clade is native to topologically variable regions in North America, where hybridization has likely played a prominent role in their diversification. Here we use a reduced-representation sequencing approach (ddRADseq) to generate a phylogenomic data set for 68 accessions representing all 22 species in the serrate leaf margin clade, as well as a number of close and distant relatives, to improve understanding of diversification in this group. Phylogenetic analyses using three methods (SVDquartets, maximum likelihood, and Bayesian) yielded highly congruent and well-resolved topologies. These phylogenies provided improved resolution relative to past analyses based on Sanger sequencing of nuclear and chloroplast DNA, and were largely consistent with taxonomic expectations based on geography and morphology. Calibration of a Bayesian phylogeny with fossil evidence produced divergence time estimates for the clade consistent with a late Oligocene origin in North America, followed by a period of elevated diversification between 12 and 5 Mya. Comparison of the ddRADseq phylogenies with a phylogeny based on Sanger-sequenced chloroplast DNA revealed five instances of pronounced discordance, illustrating the potential for chloroplast introgression, chloroplast transfer, or incomplete lineage sorting to influence organellar phylogeny. Our results improve understanding of the pattern and tempo of diversification in Juniperus, and highlight the utility of reduced-representation sequencing for resolving phylogenetic relationships in non-model organisms with reticulation and recent divergence.

Repeated intercontinental migrations and recurring hybridizations characterise the evolutionary history of yew (Taxus L.)

The genus Taxus (Taxaceae) consists of 16 genetically well-defined lineages that are predominantly distributed across the Northern hemisphere. We investigated its biogeographic origin and evolutionary history by sampling 13 chloroplast gene sequences, the nuclear internal transcribed spacers (ITS) and NEEDLY sequences for all 16 lineages. We applied Maximum Parsimony and Bayesian Inference analyses to infer their phylogenetic relationships, time-calibrated phylogenies using BEAST and inferred the ancestral area of occupancy with BioGeoBEARS. We found strong evidence for the hybrid origin of three lineages and dated these events to a rather narrow time window of 6.8-4.9 million years ago (Mya). The dated phylogenies inferred an Upper Cretaceous origin of the genus, with the extant lineages diversifying in North America much later during the Oligocene/early Miocene. Repeated migrations via the Bering land bridge to Eurasia and back were further inferred, with the return to North America as a possible result of vicariance. The diversification in Eurasia (from ~8 Mya onwards) coincided with the orogeny of the Hengduan Mountains, the intensification of the East Asian summer monsoon and the occupancy of ecological niches by lineages that experienced secondary contacts and hybridizations in the Hengduan Mountains and Qinling Mountain, especially around the Sichuan basin. We provide a hypothesis for the evolution of extant lineages of Taxus, a genus with an old and complex evolutionary history. The study highlights that the history of complex species can be unravelled with a careful dissection of phylogenetic signals.

Biogeographic diversification of Mahonia (Berberidaceae): Implications for the origin and evolution of East Asian subtropical evergreen broadleaved forests

The subtropical evergreen broadleaved forests (EBLFs) inhabit large areas of East Asia and harbor rich biodiversity and high endemism. However, the origin and evolution of biodiversity of East Asian subtropical EBLFs remain poorly understood. Here, we used Mahonia (Berberidaceae), an eastern Asian-western North American disjunct evergreen genus, to obtain new insights into the historical assembly of this biome. We present the most comprehensive phylogenetic analysis of Mahonia do date based on six nuclear and plastid loci. Using the phylogenetic framework, we estimated divergence times, reconstructed ancestral ranges, inferred evolutionary shift of habitats, and estimated diversification rates. Mahonia and each of its two groups (Orientales and Occidentales) are strongly supported as monophyletic. Mahonia originated in western North America during the late Eocene (c. 40.41 Ma) and subsequently dispersed into East Asia prior to the early Oligocene (c. 32.65 Ma). The North Atlantic Land Bridge might have played an important role in population exchanges of Mahonia between East Asia and western North America. The western North American Occidentales began to diversify in summer-dry climates and open landscapes in the early Miocene, whereas the eastern Asian Orientales began to diversify in subtropical EBLFs in the early Miocene and furthermore had a rapid lineage accumulation since the late Miocene. The net diversification rate of Mahonia in eastern Asia appeared to be higher than that in western North America, which is ascribed to lower extinction rates and ecological opportunity. Our findings suggest that western North America is a source of biodiversity of East Asian subtropical EBLFs. This biome in eastern Asia began to rise in the early Miocene and further diversified in the late Miocene, driven by the intensifying East Asian summer monsoon during these two periods.

Plastome Phylogenomic and Biogeographical Study on Thuja (Cupressaceae)

Investigating the biogeographical disjunction of East Asian and North American flora is key to understanding the formation and dynamics of biodiversity in the Northern Hemisphere. The small Cupressaceae genus Thuja, comprising five species, exhibits a typical disjunct distribution in East Asia and North America. Owing to obscure relationships, the biogeographical history of the genus remains controversial. Here, complete plastomes were employed to investigate the plastome evolution, phylogenetic relationships, and biogeographic history of Thuja. All plastomes of Thuja share the same gene content arranged in the same order. The loss of an IR was evident in all Thuja plastomes, and the B-arrangement as previously recognized was detected. Phylogenomic analyses resolved two sister pairs, T. standishii-T. koraiensis and T. occidentalis-T. sutchuenensis, with T. plicata sister to T. occidentalis-T. sutchuenensis. Molecular dating and biogeographic results suggest the diversification of Thuja occurred in the Middle Miocene, and the ancestral area of extant species was located in northern East Asia. Incorporating the fossil record, we inferred that Thuja likely originated from the high-latitude areas of North America in the Paleocene with a second diversification center in northern East Asia. The current geographical distribution of Thuja was likely shaped by dispersal events attributed to the Bering Land Bridge in the Miocene and subsequent vicariance events accompanying climate cooling. The potential effect of extinction may have profound influence on the biogeographical history of Thuja.

A Review on Worldwide Ephedra History and Story: From Fossils to Natural Products Mass Spectroscopy Characterization and Biopharmacotherapy Potential

Growing worldwide, the genus Ephedra (family Ephedraceae) had a medicinal, ecological, and economic value. The extraordinary morphological diversity suggests that Ephedra was survivor of an ancient group, and its antiquity is also supported by fossil data. It has recently been suggested that Ephedra appeared 8–32 million years ago, and a few megafossils document its presence in the Early Cretaceous. Recently, the high analytical power provided by the new mass spectrometry (MS) instruments is making the characterization of Ephedra metabolites more feasible, such as ephedrine series. In this regard, the chemical compounds isolated from crude extracts, fractions, and few isolated compounds of Ephedra species were characterized by MS-based techniques (LC-MS, LC-ESI-MS, HPLC-PDA-ESI/MS, LC-DAD-ESI/MSn, LC/Orbitrap MS, etc.). Moreover, we carry out an exhaustive review of the scientific literature on biomedicine and pharmacotherapy (anticancer, antiproliferative, anti-inflammatory, antidiabetic, antihyperlipidemic, antiarthritic, and anti-influenza activities; proapoptotic and cytotoxic potential; and so on). Equally, antimicrobial and antioxidant activities were discussed. This review is focused on all these topics, along with current studies published in the last 5 years (2015–2019) providing in-depth information for readers.

Araucarioid wood from the late Oligocene-early Miocene of Hainan Island: first fossil evidence for the genus Agathis in the Northern Hemisphere

Although many fossil and molecular data suggest migrations from Malesia and Asia to Australia appear to dominate floristic exchange between Australian and Asian rainforests, evidence is emerging that demonstrate dispersal of plant groups from Australia to Asia. In this paper, a new species Agathis ledongensis sp. nov. is described on the basis of silicified wood from the late Oligocene-early Miocene of the Qiutangling Formation in Ledong, Hainan Island, South China. It is the first fossil record of Agathis in the Northern Hemisphere, and the only known fossil evidence of its dispersal outside of Gondwana. The close affinity of the fossil wood from Ledong with the genus Agathis was confirmed by comparing quantitative traits in 31 wood samples of 20 species representing all three extant genera of the Araucariaceae. The percentage of tracheids with uniseriate pitting on radial walls is shown as an additional diagnostic trait for separating Agathis and Wollemia from Araucaria. The wood of Agathis ledongensis provides evidence for the dispersal of this important plant group from Australia, or another Gondwanan terrane, to eastern Asia based on reliable fossil data. It records the occurrence of this genus in Hainan Island by the early Miocene, i.e. at the beginning of the formation of the island chains between Australia and the South-East Asia and thus the provision of a land migration route. As the land routes between these continents were restricted at that time, the migration of Agathis to Malesia and Asia was presumably facilitated by long-distance dispersal of its winged seeds by wind.

A new macrofossil ephedroid plant with unusual bract morphology from the Lower Cretaceous Jiufotang Formation of northeastern China

BACKGROUND

The evolution of the Jehol Biota of western Liaoning in China includes three phases, initiation in the Dabeigou phase, radiation in the Yixian phase, and decline in the Jiufotang phase. Numerous ephedroid macrofossils were reported from the Lower Cretaceous Yixian Formation. However, so far none has been found in the younger Jiufotang Formation (ca. 120.3 Ma) of western Liaoning.

RESULTS

Here we report a new species Jianchangia verticillata gen. et sp. nov. with unusual morphology from the Lower Cretaceous of the Jiufotang Formation, Lamadong Village, Jianchang County, Liaoning. This species is the first record of gnetophytes from the Jiufotang Formation. It is similar to other ephedroid species from the Yixian Formation in possessing linear leaves with parallel veins, jointed shoots with swollen nodes and longitudinally furrowed internodes, and ovulate cones possessing two whorls of bracts enclosing two chlamydosperms, but differs from all known species by the ovulate cone having multiple fine linear verticillate bracts.

CONCLUSIONS

This study expands our knowledge about the diversity of early gnetophytes in the Lower Cretaceous, and demonstrates the lineage continuity of gnetophytes from the Yixian Formation to the younger Jiufotang Formation.

The complete mitochondrial genome of Taxus cuspidata (Taxaceae): eight protein-coding genes have transferred to the nuclear genome

BACKGROUND

Gymnosperms represent five of the six lineages of seed plants. However, most sequenced plant mitochondrial genomes (mitogenomes) have been generated for angiosperms, whereas mitogenomic sequences have been generated for only six gymnosperms. In particular, complete mitogenomes are available for all major seed plant lineages except Conifer II (non-Pinaceae conifers or Cupressophyta), an important lineage including six families, which impedes a comprehensive understanding of the mitogenomic diversity and evolution in gymnosperms.

RESULTS

Here, we report the complete mitogenome of Taxus cuspidata in Conifer II. In comparison with previously released gymnosperm mitogenomes, we found that the mitogenomes of Taxus and Welwitschia have lost many genes individually, whereas all genes were identified in the mitogenomes of Cycas, Ginkgo and Pinaceae. Multiple tRNA genes and introns also have been lost in some lineages of gymnosperms, similar to the pattern observed in angiosperms. In general, gene clusters could be less conserved in gymnosperms than in angiosperms. Moreover, fewer RNA editing sites were identified in the Taxus and Welwitschia mitogenomes than in other mitogenomes, which could be correlated with fewer introns and frequent gene losses in these two species.

CONCLUSIONS

We have sequenced the Taxus cuspidata mitogenome, and compared it with mitogenomes from the other four gymnosperm lineages. The results revealed the diversity in size, structure, gene and intron contents, foreign sequences, and mutation rates of gymnosperm mitogenomes, which are different from angiosperm mitogenomes.