Resolving the Speciation Patterns and Evolutionary History of the Intercontinental Disjunct Genus Corylus (Betulaceae) Using Genome-Wide SNPs

Hazelnut allergome overview and Cor a gRNAs identification

BACKGROUND

Corylus species (hazelnuts) are a valuable source of nutrients and are widely consumed worldwide. Nevertheless, Corylus avellana (Cor a) contains 13 allergens (Cor a 1, Cor a 2, Cor a 6, Cor a 8, Cor a 9, Cor a 10, Cor a 11, Cor a 12, Cor a 13, Cor a 14, Cor a 15, Cor a 16, and Cor a TLP) that have been deposited into the official database (WHO/IUIS) for allergen nomenclature. The recent availability of several Corylus genomes provided opportunities to explore allergome variability, and thus to develop hypoallergenic varieties using modern biotech approaches. Certainly, the identification of CRISPR-Cas9 guide RNA (gRNA) is a pivotal step in achieving this goal. User-friendly web tools include limited reference genomes to design CRISPR-Cas9 gRNAs, while bioinformatic software for custom analysis require advanced command-line skills.

RESULTS

This work explored the evolutionary trajectories of allergenic Cor a homologs in C. avellana, C. americana, C. heterophylla, and C. mandshurica genome assemblies. 52 Cor a orthologs were found in the analyzed species, and a recent tandem duplication of Cor a 1 was found in C. americana. Three new gene models were predicted in C. avellana and C. mandshurica for Cor a 16 and Cor a 10. Additionally, we identified 56 Cor a isoallergens, of which ten Cor a isoforms. Furthermore, phylogenetic analysis sheds light on the evolutionary dynamics of three hazelnut allergens revealing the evolutionary complexity of Cor a 1, Cor a 2, and Cor a TLP within the Corylus genus. A list of multiple gRNAs designed for the CRISPR-Cas9 system was provided for the singular and multiple silencing of Cor a homologs in each Corylus genome.

CONCLUSIONS

This study enhances our knowledge on the evolutionary path of Cor a allergens among Corylus species and provides highly accurate on-target guides targeting hazelnut allergome.

Population genomics reveals demographic history and selection signatures of hazelnut (Corylus)

Hazelnut (Corylus spp.) is known as one of the four famous tree nuts in the world due to its pleasant taste and nutritional benefits. However, hazelnut promotion worldwide is increasingly challenged by global climate change, limiting its production to a few regions. Focusing on the eurytopic Section Phyllochlamys, we conducted whole-genome resequencing of 125 diverse accessions from five geo-ecological zones in Eurasia to elucidate the genomic basis of adaptation and improvement. Population structure inference outlined five distinct genetic lineages corresponding to climate conditions and breeding background, and highlighted the differentiation between European and Asian lineages. Demographic dynamics and ecological niche modeling revealed that Pleistocene climatic oscillations dominantly shaped the extant genetic patterns, and multiple environmental factors have contributed to the lineage divergence. Whole-genome scans identified 279, 111, and 164 selective sweeps that underlie local adaptation in Corylus heterophylla, Corylus kweichowensis, and Corylus yunnanensis, respectively. Relevant positively selected genes were mainly involved in regulating signaling pathways, growth and development, and stress resistance. The improvement signatures of hybrid hazelnut were concentrated in 312 and 316 selected genes, when compared to C. heterophylla and Corylus avellana, respectively, including those that regulate protein polymerization, photosynthesis, and response to water deprivation. Among these loci, 22 candidate genes were highly associated with the regulation of biological quality. Our study provides insights into evolutionary processes and the molecular basis of how sibling species adapt to contrasting environments, and offers valuable resources for future climate-resilient breeding.

Evolutionary origins of the eastern North American-Mesoamerican floristic disjunction: Current status and future prospects

Biogeographic disjunction patterns, where multiple taxa are shared between isolated geographic areas, represent excellent systems for investigating the historical assembly of modern biotas and fundamental biological processes such as speciation, diversification, niche evolution, and evolutionary responses to climate change. Studies on plant genera disjunct across the northern hemisphere, particularly between eastern North America (ENA) and eastern Asia (EAS), have yielded tremendous insight on the geologic history and assembly of rich temperate floras. However, one of the most prevalent disjunction patterns involving ENA forests has been largely overlooked: that of taxa disjunct between ENA and cloud forests of Mesoamerica (MAM), with examples including Acer saccharum, Liquidambar styraciflua, Cercis canadensis, Fagus grandifolia, and Epifagus virginiana. Despite the remarkable nature of this disjunction pattern, which has been recognized for over 75 years, there have been few recent efforts to empirically examine its evolutionary and ecological origins. Here I synthesize previous systematic, paleobotanical, phylogenetic, and phylogeographic studies to establish what is known about this disjunction pattern to provide a roadmap for future research. I argue that this disjunction pattern, and the evolution and fossil record of the Mexican flora more broadly, represents a key missing piece in the broader puzzle of northern hemisphere biogeography. I also suggest that the ENA-MAM disjunction represents an excellent system for examining fundamental questions about how traits and life history strategies mediate plant evolutionary responses to climate change and for predicting how broadleaf temperate forests will respond to the ongoing climatic pressures of the Anthropocene.

First rhyncaphytoptine mite (Eriophyoidea, Diptilomiopidae) parasitizing American hazelnut (Corylus americana): molecular identification, confocal microscopy, and phylogenetic position

The plant genus Corylus is an economically important crop, valued especially for its nuts. Numerous pathogens and harmful phytophagous arthropods are known to damage hazelnuts. We report on a new eriophyoid mite, Rhyncaphytoptus corylivagrans n. sp., and the first record of Coptophylla lamimani both collected from leaves of American hazelnut (Corylus americana) in North Carolina, USA. Including our new data, the complex of eriophyoids from Corylus comprises 15 species from three families: Phytoptidae (2 spp.), Eriophyidae (11 spp.), and Diptilomiopidae (2 spp.). We obtained sequences of three genes (Cox1, D1-D5 28S, and ITS1-5.8S-ITS2), applied BLAST and tree-based approaches for identification of R. corylivagrans n. sp., and performed the first molecular phylogenetic analysis focused on Rhyncaphytoptinae. Among the three genes, Cox1 showed better power when used for BLAST searches. Combined molecular phylogenetic analyses inferred R. corylivagrans n. sp. as sister to R. betulae, determined several moderately supported host-specific lineages of rhyncaphytoptines, and indicated a close relationship of the new species with members of the genus Rhinotergum. In two Rhinotergum spp. from Rosaceae, confocal microscopy revealed a new structure, the needle-like anterior process of the prodorsal shield, which is absent in R. corylivagrans n. sp. Additionally, the elements of the anal secretory apparatus presumably associated with silk-production and hypothesized as a synapomorphy of Eriophyoidea, were detected in the new species, providing the first documented report of this structure in Diptilomiopidae. Our study contributes to knowledge on the biodiversity of phytoparasites associated with hazelnuts and calls for future comparative phylogenetics of Diptilomiopidae.

Species delimitation and hybridization history of a hazel species complex

BACKGROUND AND AIMS

Hybridization increases species adaptation and biodiversity but also obscures species boundaries. In this study, species delimitation and hybridization history were examined within one Chinese hazel species complex (Corylus chinensis-Corylus fargesii). Two species including four varieties have already been described for this complex, with overlapping distributions.

METHODS

A total of 322 trees from 44 populations of these four varieties across their ranges were sampled for morphological and molecular analyses. Climatic datasets based on 108 geographical locations were used to evaluate their niche differentiations. Flowering phenology was also observed for two co-occurring species or varieties.

KEY RESULTS

Four statistically different phenotypic clusters were revealed, but these clusters were highly inconsistent with the traditional taxonomic groups. All the clusters showed statistically distinct niches, with complete or partial geographical isolation. Only two clusters displayed a distributional overlap, but they had distinct flowering phenologies at the site where they co-occurred. Population-level evidence based on the genotypes of ten simple sequence repeat loci supported four phenotypic clusters. In addition, one cluster was shown to have an admixed genetic composition derived from the other three clusters through repeated historical hybridizations.

CONCLUSIONS

Based on our new evidence, it is better to treat the four clusters identified here as four independent species. One of them was shown to have an admixed genetic composition derived from the other three through repeated historical hybridizations. This study highlights the importance of applying integrative and statistical methods to infer species delimitations and hybridization history. Such a protocol should be adopted widely for future taxonomic studies.

Molecular phylogeny of the phytoparasitic mite family Phytoptidae (Acariformes: Eriophyoidea) identified the female genitalic anatomy as a major macroevolutionary factor and revealed multiple origins of gall induction

Phytoptidae s.str. is a lineage of eriophyoid mites associated with angiosperms. Based on representative taxon sampling and four gene markers (COI, HSP70, 18S, and 28S), we inferred the molecular phylogeny of this group and performed comparative analyses of cuticle-lined female internal genitalia. Although basal relationships were unclear, several well supported clades were recovered. These clades were supported by geography, host associations, and female genital anatomy, but contradicted the current morphology-based systematics. The monophyly of each of five conventional supraspecific groupings (Fragariocoptes, Phytoptus, Phytoptinae, Sierraphytoptinae, and Sierraphytoptini) is rejected based on a series of statistical tests. Additionally, four morphological characters (the absence of tibial solenidion φ and opisthosomal seta c1, presence of telosomal pseudotagma, and 'morphotype') were found to be homoplasies that cannot be used to confidently delimit supraspecific lineages of phytoptids. However, our molecular topology was highly congruent with female genital characters. Eight molecular clades were unambiguously supported by the shapes and topography of the spermathecal apparatus and genital apodemes. This suggests that the female genital anatomy could be an important factor affecting cladogenesis in Phytoptidae, a conclusion contrasting with the general expectation that host characteristics should be a major macroevolutionary force influencing the evolution of host-specific symbionts. Indeed, despite the high host-specificity, there were no apparent cophylogenetic patterns. Furthermore, we show that gall-inducing ability evolved multiple times in phytoptids. Because gall formation creates nearly instantaneous niche partitioning and the potential loss or reduction of gene flow, we hypothesize that it could be an important evolutionary factor affecting speciation within different host-associated clades of phytoptid mites.

Chloroplast genomes of seven species of Coryloideae (Betulaceae): structures and comparative analysis

Coryloideae is a subfamily in the family Betulaceae consisting of four extant genera: Carpinus, Corylus, Ostrya, and Ostryopsis. We sequenced the plastomes of six species of Corylus and one species of Ostryopsis for comparative and phylogenetic analyses. The plastomes are 159-160 kb long and possess typical quadripartite cp architecture. The plastomes show moderate divergence and conserved arrangement. Five mutational hotspots were identified by comparing the plastomes of seven species of Coryloideae: trnG-atpA, trnF-ndhJ, accD-psaI, ndhF-ccsA, and ycf1. We assembled the most complete phylogenomic tree for the family Betulaceae using 68 plastomes. Our cp genomic sequence phylogenetic analyses placed Carpinus, Ostrya, and Ostryopsis in a clade together and left Corylus in a separate clade. Within the genus Corylus, these analyses indicate the existence of five subclades reflecting the phylogeographical relationships among the species. The data offer significant genetic information for the identification of species of the Coryloideae, taxonomic and phylogenetic studies, and molecular breeding.

Repeated long-distance dispersal and convergent evolution in hazel

Closely related species with a worldwide distribution provide an opportunity to understand evolutionary and biogeographic processes at a global scale. Hazel (Corylus) is an economically important genus of tree and shrub species found in temperate regions of Asia, North America and Europe. Here we use multiple nuclear and chloroplast loci to estimate a time-calibrated phylogenetic tree of the genus Corylus. We model the biogeographic history of this group and the evolutionary history of tree and shrub form. We estimate that multiple Corylus lineages dispersed long distances between Europe and Asia and colonised North America from Asia in multiple independent events. The geographic distribution of tree versus shrub form of species appears to be the result of 4–5 instances of convergent evolution in the past 25 million years. We find extensive discordance between our nuclear and chloroplast trees and potential evidence for chloroplast capture in species with overlapping ranges, suggestive of past introgression. The important crop species C. avellana is estimated to be closely related to C. maxima, C. heterophylla var. thunbergii and the Colurnae subsection. Our study provides a new phylogenetic hypothesis or Corylus and reveals how long-distance dispersal can shape the distribution of biodiversity in temperate plants.