Lineage-specific Duplications Research Articles

High-quality haplotype-resolved chromosome assembly provides evolutionary insights and targeted steviol glycosides (SGs) biosynthesis in Stevia rebaudiana Bertoni.

Stevia rebaudiana Bertoni is popular source of plant-derived low/no-calorie natural sweeteners (LNCSs), collectively known as steviol glycosides (SGs). Nevertheless, genetic predisposition for targeted biosynthesis of SGs is complex due to multi-substrate functionality of key uridine diphosphate glycosyltransferases (UGTs). Here, we created a high-quality monoploid assembly of 1.34 Gb with N50 value of 110 Mb, 55 551 predicted protein-coding genes, and ~80% repetitive regions in Rebaudioside-A (Reb-A) enriched cultivar of S. rebaudiana. Additionally, a haplotype-based chromosome assembly consisting of haplotype A and haplotype B with an overall genome size of 2.33Gb was resolved, harbouring 639 634 variants including single nucleotide polymorphisms (SNPs), indels and structural variants (SVs). Furthermore, a lineage-specific whole genome duplication analysis revealed that gene families encoding UGTs and Cytochrome-P450 (CYPs) were tandemly duplicated. Additionally, expression analysis revealed five tandemly duplicated gene copies of UGT76G1 having significant correlations with Reb-A content, and identified key residue (leu200val) in the glycosylation of Reb-A. Furthermore, missense variations identified in the acceptor region of UGT76G1 in haplotype resolve genome, transcriptional and molecular docking analysis were confirmed with resequencing of 10 diverse stevia genotypes (~25X). Gene regulatory network analysis identified key transcription factors (MYB, bHLH, bZIP and AP2-ERF) as potential regulators of SG biosynthesis. Overall, this study provides haplotype-resolved chromosome-level genome assembly for genome editing and enhancing breeding efforts for targeted biosynthesis of SGs in S. rebaudiana.

Complete sequencing of ape genomes.

We present haplotype-resolved reference genomes and comparative analyses of six ape species, namely: chimpanzee, bonobo, gorilla, Bornean orangutan, Sumatran orangutan, and siamang. We achieve chromosome-level contiguity with unparalleled sequence accuracy (<1 error in 500,000 base pairs), completely sequencing 215 gapless chromosomes telomere-to-telomere. We resolve challenging regions, such as the major histocompatibility complex and immunoglobulin loci, providing more in-depth evolutionary insights. Comparative analyses, including human, allow us to investigate the evolution and diversity of regions previously uncharacterized or incompletely studied without bias from mapping to the human reference. This includes newly minted gene families within lineage-specific segmental duplications, centromeric DNA, acrocentric chromosomes, and subterminal heterochromatin. This resource should serve as a definitive baseline for all future evolutionary studies of humans and our closest living ape relatives.

Divergent evolution of NLR genes in the genus Glycine: impacts of annuals and perennials' life history strategies.

Within the family Fabaceae, the genus Glycine is composed of two subgenera annuals (2n=40) and perennials. This life strategy transition may have differentially affected the evolution of various gene families. Its cultivated species G. max has high level of susceptibility to major pathogens including viruses, bacteria and fungi. Understanding nucleotide-binding domain leucine-rich repeat (NLR) genes evolution in soybean is of paramount importance due to their central role in plant immunity and their potential in improving disease resistance in soybean cultivars. In this study, we investigated the significance of this annual-perennial transition on the macroevolution of NLR genes in the genus Glycine. Our results reveal a remarkable distinction between annual species such as Glycine max and Glycine soja, which exhibit an expanded NLRome compared to perennial species (G. cyrtoloba, G. stenophita, G.dolichocarpa, G. falcata, G. syndetika, G. latifolia and G. tomentella). Our evolutionary timescale analysis pinpoints recent accelerated gene duplication events for this expansion, which occurred between 0.1 and 0.5 million years ago, driven predominantly by lineage-specific and terminal duplications. In contrast, perennials initially experienced significant contraction during the diploidisation phase following the Glycine-specific whole-genome duplication event (~10 million years ago). Despite the reduction in the NLRome, perennial lineages exhibit a unique and highly diversified repertoire of NLR genes with limited interspecies synteny. The investigation of gene gain and loss ratios revealed that this diversification resulted from the birth of novel genes following individual speciation events. Among perennials, G. latifolia, a well-known resistance resource, has the highest ratio of these novel genes in the tertiary gene pool. Our study suggests evolutionary mechanisms, including recombination and transposition, as potential drivers for the emergence of these novel genes. This study also provides evidence for the unbalanced expansion of the NLRome in the Dt subgenome compared with the At subgenome in the young allopolyploid G.dolichocarpa. To the best of our knowledge, this is the first study to investigate the effect of annuality and perenniality life transition on the evolution of NLR genes in the genus Glycine to identify its genomics resources for improving the resistance of soybean crop with global importance on the economy and food security.

Bioinformatic Analysis of Roquin Family Reveals Their Potential Role in Immune System.

The Roquin family is a recognized RNA-binding protein family that plays vital roles in regulating the expression of pro-inflammatory target gene mRNA during the immune process in mammals. However, the evolutionary status of the Roquin family across metazoans remains elusive, and limited studies are found in fish species. In this study, we discovered that the RC3H genes underwent a single round of gene duplication from a primitive ancestor during evolution from invertebrates to vertebrates. Furthermore, there were instances of species-specific gene loss events or teleost lineage-specific gene duplications throughout evolution. Domain/motif organization and selective pressure analysis revealed that Roquins exhibit high homology both within members of the family within the same species and across species. The three rc3h genes in zebrafish displayed similar expression patterns in early embryos and adult tissues, with rc3h1b showing the most prominent expression among them. Additionally, the promoter regions of the zebrafish rc3h genes contained numerous transcription factor binding sites similar to those of mammalian homologs. Moreover, the interaction protein network of Roquin and the potential binding motif in the 3'-UTR of putative target genes analysis both indicated that Roquins have the potential to degrade target mRNA through mechanisms similar to those of mammalian homologs. These findings shed light on the evolutionary history of Roquin among metazoans and hypothesized their role in the immune systems of zebrafish.

Lineage-specific gene duplication and expansion of DUF1216 gene family in Brassicaceae.

Proteins containing domain of unknown function (DUF) are prevalent in eukaryotic genome. The DUF1216 proteins possess a conserved DUF1216 domain resembling to the mediator protein of Arabidopsis RNA polymerase II transcriptional subunit-like protein. The DUF1216 family are specifically existed in Brassicaceae, however, no comprehensive evolutionary analysis of DUF1216 genes have been performed. We performed a first comprehensive genome-wide analysis of DUF1216 proteins in Brassicaceae. Totally 284 DUF1216 genes were identified in 27 Brassicaceae species and classified into four subfamilies on the basis of phylogenetic analysis. The analysis of gene structure and conserved motifs revealed that DUF1216 genes within the same subfamily exhibited similar intron/exon patterns and motif composition. The majority members of DUF1216 genes contain a signal peptide in the N-terminal, and the ninth position of the signal peptide in most DUF1216 is cysteine. Synteny analysis revealed that segmental duplication is a major mechanism for expanding of DUF1216 genes in Brassica oleracea, Brassica juncea, Brassica napus, Lepidium meyneii, and Brassica carinata, while in Arabidopsis thaliana and Capsella rubella, tandem duplication plays a major role in the expansion of the DUF1216 gene family. The analysis of Ka/Ks (non-synonymous substitution rate/synonymous substitution rate) ratios for DUF1216 paralogous indicated that most of gene pairs underwent purifying selection. DUF1216 genes displayed a specifically high expression in reproductive tissues in most Brassicaceae species, while its expression in Brassica juncea was specifically high in root. Our studies offered new insights into the phylogenetic relationships, gene structures and expressional patterns of DUF1216 members in Brassicaceae, which provides a foundation for future functional analysis.

Copy number and selection of MHC genes in ruminants are related to habitat, average life span and diet

The ruminants, as the main group of livestock, have been extensively studied in terms of their physiology, endocrinology, biochemistry, genetics, and nutrition. Despite the wide geographic distribution and habitat diversity of animals in this group, their ecology and evolution remain poorly understood. In this study, we analyzed the gene copy number, selection, and ecological and evolutionary processes that have affected the evolution of major histocompatibility complex (MHC) genes across ruminant lineages based on available genomic data. The 51 species analyzed represented all six families of ruminants. Our finding indicated that the architecture of the MHC region is conserved in ruminants, but with variable copy numbers of MHC-I, MHC-IIA, and MHC-IIB genes. No lineage-specific gene duplication was observed in the MHC genes. The phylogenetic generalized least squares regression (PGLS) model revealed association between ecological and biological factors (habitat and lifespan) and gene duplication in DQA and DQB, but not in DRB. The selection pressure of DQA and DQB were related with lifespan, diet, and the ratio of genetic repeat elements. These results suggest that the MHC evolution in ruminants, including copy number and selection, has been influenced by genetic repeat elements, pathogen exposure risk, and intrinsic cost of possessing multiple MHC genes.

Comparative transcriptome analysis between rhesus macaques ( Macaca mulatta) and crab-eating macaques ( M. fascicularis).

Understanding gene expression variations between species is pivotal for deciphering the evolutionary diversity in phenotypes. Rhesus macaques ( Macaca mulatta, MMU) and crab-eating macaques ( M. fascicularis, MFA) serve as crucial nonhuman primate biomedical models with different phenotypes. To date, however, large-scale comparative transcriptome research between these two species has not yet been fully explored. Here, we conducted systematic comparisons utilizing newly sequenced RNA-seq data from 84 samples (41 MFA samples and 43 MMU samples) encompassing 14 common tissues. Our findings revealed a small fraction of genes (3.7%) with differential expression between the two species, as well as 36.5% of genes with tissue-specific expression in both macaques. Comparison of gene expression between macaques and humans indicated that 22.6% of orthologous genes displayed differential expression in at least two tissues. Moreover, 19.41% of genes that overlapped with macaque-specific structural variants showed differential expression between humans and macaques. Of these, the FAM220A gene exhibited elevated expression in humans compared to macaques due to lineage-specific duplication. In summary, this study presents a large-scale transcriptomic comparison between MMU and MFA and between macaques and humans. The discovery of gene expression variations not only enhances the biomedical utility of macaque models but also contributes to the wider field of primate genomics.

Genomic survey maps differences in the molecular complement of vesicle formation machinery between Giardia intestinalis assemblages.

Giardia intestinalis is a globally important microbial pathogen with considerable public health, agricultural, and economic burden. Genome sequencing and comparative analyses have elucidated G. intestinalis to be a taxonomically diverse species consisting of at least eight different sub-types (assemblages A-H) that can infect a great variety of animal hosts, including humans. The best studied of these are assemblages A and B which have a broad host range and have zoonotic transmissibility towards humans where clinical Giardiasis can range from asymptomatic to diarrheal disease. Epidemiological surveys as well as previous molecular investigations have pointed towards critical genomic level differences within numerous molecular pathways and families of parasite virulence factors within assemblage A and B isolates. In this study, we explored the necessary machinery for the formation of vesicles and cargo transport in 89 Canadian isolates of assemblage A and B G. intestinalis. Considerable variability within the molecular complement of the endolysosomal ESCRT protein machinery, adaptor coat protein complexes, and ARF regulatory system have previously been reported. Here, we confirm inter-assemblage, but find no intra-assemblage variation within the trafficking systems examined. This variation includes losses of subunits belonging to the ESCRTIII as well as novel lineage specific duplications in components of the COPII machinery, ARF1, and ARFGEF families (BIG and CYTH). Since differences in disease manifestation between assemblages A and B have been controversially reported, our findings may well have clinical implications and even taxonomic, as the membrane trafficking system underpin parasite survival, pathogenesis, and propagation.

Genomic and transcriptomic survey of bryozoan Hox and ParaHox genes with emphasis on phylactolaemate bryozoans

BackgroundBryozoans are mostly sessile aquatic colonial invertebrates belonging to the clade Lophotrochozoa, which unites many protostome bilaterian phyla such as molluscs, annelids and brachiopods. While Hox and ParaHox genes have been extensively studied in various lophotrochozoan lineages, investigations on Hox and ParaHox gene complements in bryozoans are scarce.ResultsHerein, we present the most comprehensive survey of Hox and ParaHox gene complements in bryozoans using four genomes and 35 transcriptomes representing all bryozoan clades: Cheilostomata, Ctenostomata, Cyclostomata and Phylactolaemata. Using similarity searches, phylogenetic analyses and detailed manual curation, we have identified five Hox genes in bryozoans (pb, Dfd, Lox5, Lox4 and Post2) and one ParaHox gene (Cdx). Interestingly, we observed lineage-specific duplication of certain Hox and ParaHox genes (Dfd, Lox5 and Cdx) in some bryozoan lineages.ConclusionsThe bryozoan Hox cluster does not retain the ancestral lophotrochozoan condition but appears relatively simple (includes only five genes) and broken into two genomic regions, characterized by the loss and duplication of serval genes. Importantly, bryozoans share the lack of two Hox genes (Post1 and Scr) with their proposed sister-taxon, Phoronida, which suggests that those genes were missing in the most common ancestor of bryozoans and phoronids.

Origin and early divergence of tandem duplicated sorbitol transporter genes in Rosaceae: insights from evolutionary analysis of the SOT gene family in angiosperms.

Sorbitol is a critical photosynthate and storage substance in the Rosaceae family. Sorbitol transporters (SOTs) play a vital role in facilitating sorbitol allocation from source to sink organs and sugar accumulation in sink organs. While prior research has addressed gene duplications within the SOT gene family in Rosaceae, the precise origin and evolutionary dynamics of these duplications remain unclear, largely due to the complicated interplay of whole genome duplications and tandem duplications. Here, we investigated the synteny relationships among all identified Polyol/Monosaccharide Transporter (PLT) genes in 61 angiosperm genomes and SOT genes in representative genomes within the Rosaceae family. By integrating phylogenetic analyses, we elucidated the lineage-specific expansion and syntenic conservation of PLTs and SOTs across diverse plant lineages. We found that Rosaceae SOTs, as PLT family members, originated from a pair of tandemly duplicated PLT genes within Class III-A. Furthermore, our investigation highlights the role of lineage-specific and synergistic duplications in Amygdaloideae in contributing to the expansion of SOTs in Rosaceae plants. Collectively, our findings provide insights into the genomic origins, duplication events, and subsequent divergence of SOT gene family members. Such insights lay a crucial foundation for comprehensive functional characterizations in future studies.

Identification and characterization of the cupin_1 domain-containing proteins in ma bamboo (Dendrocalamus latiflorus) and their potential role in rhizome sprouting.

Cupin_1 domain-containing protein (CDP) family, which is a member of the cupin superfamily with the most diverse functions in plants, has been found to be involved in hormone pathways that are closely related to rhizome sprouting (RS), a vital form of asexual reproduction in plants. Ma bamboo is a typical clumping bamboo, which mainly reproduces by RS. In this study, we identified and characterized 53 Dendrocalamus latiflorus CDP genes and divided them into seven subfamilies. Comparing the genetic structures among subfamilies showed a relatively conserved gene structure within each subfamily, and the number of cupin_1 domains affected the conservation among D. latiflorus CDP genes. Gene collinearity results showed that segmental duplication and tandem duplication both contributed to the expansion of D. latiflorus CDP genes, and lineage-specific gene duplication was an important factor influencing the evolution of CDP genes. Expression patterns showed that CDP genes generally had higher expression levels in germinating underground buds, indicating that they might play important roles in promoting shoot sprouting. Transcription factor binding site prediction and co-expression network analysis indicated that D. latiflorus CDPs were regulated by a large number of transcription factors, and collectively participated in rhizome buds and shoot development. This study significantly provided new insights into the evolutionary patterns and molecular functions of CDP genes, and laid a foundation for further studying the regulatory mechanisms of plant rhizome sprouting.

Control of social status by sex steroids: insights from teleost fishes

Many animals live in highly social environments, in which individuals must behave in a way that enables them to survive and live harmoniously among conspecifics. Dominance hierarchies are typical among social species and are essential for determining and preserving stability within social groups. Although there is considerable evidence that sex steroid hormones regulate behaviors associated with dominance, such as aggression and mating, fewer studies have examined the role of these hormones in controlling social status, especially in species that exhibit social hierarchies. Furthermore, despite this research, we know remarkably little about the precise neural and molecular mechanisms through which sex steroids modulate traits associated with social rank. Here, we review the neuroendocrine regulation of social status by sex steroids in teleost fishes, the largest and most diverse vertebrate group that shows extensive variation in reproductive systems and social structures between species. First, we describe the function of sex steroids and novel steroid-related genes that teleost fishes possess due to a lineage-specific whole-genome duplication event. Then, we discuss correlational, pharmacological, and molecular genetic studies on the control of social status by sex steroids in teleost fishes, including recent studies that have implemented gene editing technologies, such as CRISPR/Cas9. Finally, we argue that gene editing approaches in teleost studies, within both integrative and comparative frameworks, will be vital for elucidating the role of sex steroids in controlling social rank and characterizing their neural and molecular mechanisms of action. Collectively, ongoing and future research in these species will provide novel insight into the evolution of the regulation of social status by sex steroids and other neuroendocrine substrates across vertebrates.

Comparative genomics of the T cell receptor μ locus in marsupials and monotremes.

T cells are a primary component of the vertebrate adaptive immune system. There are three mammalian T cell lineages based on their T cell receptors (TCR). The αβ T cells and γδ T cells are ancient and found broadly in vertebrates. The more recently discovered γμ T cells are uniquely mammalian and only found in marsupials and monotremes. In this study, we compare the TCRμ locus (TRM) across the genomes of two marsupials, the gray short-tailed opossum and Tasmanian devil, and one monotreme, the platypus. These analyses revealed lineage-specific duplications, common to all non-eutherian mammals described. There is conserved synteny in the TRM loci of both marsupials but not in the monotreme. Our results are consistent with an ancestral cluster organization which was present in the last common mammalian ancestor which underwent lineage-specific duplications and divergence among the non-eutherian mammals.

Nematostella vectensis exemplifies the exceptional expansion and diversity of opsins in the eyeless Hexacorallia

BackgroundOpsins are the primary proteins responsible for light detection in animals. Cnidarians (jellyfish, sea anemones, corals) have diverse visual systems that have evolved in parallel with bilaterians (squid, flies, fish) for hundreds of millions of years. Medusozoans (e.g., jellyfish, hydroids) have evolved eyes multiple times, each time independently incorporating distinct opsin orthologs. Anthozoans (e.g., corals, sea anemones,) have diverse light-mediated behaviors and, despite being eyeless, exhibit more extensive opsin duplications than medusozoans. To better understand the evolution of photosensitivity in animals without eyes, we increased anthozoan representation in the phylogeny of animal opsins and investigated the large but poorly characterized opsin family in the sea anemone Nematostella vectensis.ResultsWe analyzed genomic and transcriptomic data from 16 species of cnidarians to generate a large opsin phylogeny (708 sequences) with the largest sampling of anthozoan sequences to date. We identified 29 opsins from N. vectensis (NvOpsins) with high confidence, using transcriptomic and genomic datasets. We found that lineage-specific opsin duplications are common across Cnidaria, with anthozoan lineages exhibiting among the highest numbers of opsins in animals. To establish putative photosensory function of NvOpsins, we identified canonically conserved protein domains and amino acid sequences essential for opsin function in other animal species. We show high sequence diversity among NvOpsins at sites important for photoreception and transduction, suggesting potentially diverse functions. We further examined the spatiotemporal expression of NvOpsins and found both dynamic expression of opsins during embryonic development and sexually dimorphic opsin expression in adults.ConclusionsThese data show that lineage-specific duplication and divergence has led to expansive diversity of opsins in eyeless cnidarians, suggesting opsins from these animals may exhibit novel biochemical functions. The variable expression patterns of opsins in N. vectensis suggest opsin gene duplications allowed for a radiation of unique sensory cell types with tissue- and stage-specific functions. This diffuse network of distinct sensory cell types could be an adaptive solution for varied sensory tasks experienced in distinct life history stages in Anthozoans.

Long-Read Sequencing Reveals Rapid Evolution of Immunity- and Cancer-Related Genes in Bats.

Bats are exceptional among mammals for their powered flight, extended lifespans, and robust immune systems and therefore have been of particular interest in comparative genomics. Using the Oxford Nanopore Technologies long-read platform, we sequenced the genomes of two bat species with key phylogenetic positions, the Jamaican fruit bat (Artibeus jamaicensis) and the Mesoamerican mustached bat (Pteronotus mesoamericanus), and carried out a comprehensive comparative genomic analysis with a diverse collection of bats and other mammals. The high-quality, long-read genome assemblies revealed a contraction of interferon (IFN)-α at the immunity-related type I IFN locus in bats, resulting in a shift in relative IFN-ω and IFN-α copy numbers. Contradicting previous hypotheses of constitutive expression of IFN-α being a feature of the bat immune system, three bat species lost all IFN-α genes. This shift to IFN-ω could contribute to the increased viral tolerance that has made bats a common reservoir for viruses that can be transmitted to humans. Antiviral genes stimulated by type I IFNs also showed evidence of rapid evolution, including a lineage-specific duplication of IFN-induced transmembrane genes and positive selection in IFIT2. In addition, 33 tumor suppressors and 6 DNA-repair genes showed signs of positive selection, perhaps contributing to increased longevity and reduced cancer rates in bats. The robust immune systems of bats rely on both bat-wide and lineage-specific evolution in the immune gene repertoire, suggesting diverse immune strategies. Our study provides new genomic resources for bats and sheds new light on the extraordinary molecular evolution in this critically important group of mammals.

Genome-wide analysis of the MADS-box gene family in Lonicera japonica and a proposed floral organ identity model

BackgroundLonicera japonica Thunb. is widely used in traditional Chinese medicine. Medicinal L. japonica mainly consists of dried flower buds and partially opened flowers, thus flowers are an important quality indicator. MADS-box genes encode transcription factors that regulate flower development. However, little is known about these genes in L. japonica.ResultsIn this study, 48 MADS-box genes were identified in L. japonica, including 20 Type-I genes (8 Mα, 2 Mβ, and 10 Mγ) and 28 Type-II genes (26 MIKCc and 2 MIKC*). The Type-I and Type-II genes differed significantly in gene structure, conserved domains, protein structure, chromosomal distribution, phylogenesis, and expression pattern. Type-I genes had a simpler gene structure, lacked the K domain, had low protein structure conservation, were tandemly distributed on the chromosomes, had more frequent lineage-specific duplications, and were expressed at low levels. In contrast, Type-II genes had a more complex gene structure; contained conserved M, I, K, and C domains; had highly conserved protein structure; and were expressed at high levels throughout the flowering period. Eleven floral homeotic MADS-box genes that are orthologous to the proposed Arabidopsis ABCDE model of floral organ identity determination, were identified in L. japonica. By integrating expression pattern and protein interaction data for these genes, we developed a possible model for floral organ identity determination.ConclusionThis study genome-widely identified and characterized the MADS-box gene family in L. japonica. Eleven floral homeotic MADS-box genes were identified and a possible model for floral organ identity determination was also developed. This study contributes to our understanding of the MADS-box gene family and its possible involvement in floral organ development in L. japonica.

NcOrtho: efficient and reliable identification of miRNA orthologs.

MicroRNAs (miRNAs) are post-transcriptional regulators that finetune gene expression via translational repression or degradation of their target mRNAs. Despite their functional relevance, frameworks for the scalable and accurate detection of miRNA orthologs are missing. Consequently, there is still no comprehensive picture of how miRNAs and their associated regulatory networks have evolved. Here we present ncOrtho, a synteny informed pipeline for the targeted search of miRNA orthologs in unannotated genome sequences. ncOrtho matches miRNA annotations from multi-tissue transcriptomes in precision, while scaling to the analysis of hundreds of custom-selected species. The presence-absence pattern of orthologs to 266 human miRNA families across 402 vertebrate species reveals four bursts of miRNA acquisition, of which the most recent event occurred in the last common ancestor of higher primates. miRNA families are rarely modified or lost, but notable exceptions for both events exist. miRNA co-ortholog numbers faithfully indicate lineage-specific whole genome duplications, and miRNAs are powerful markers for phylogenomic analyses. Their exceptionally low genetic diversity makes them suitable to resolve clades where the phylogenetic signal is blurred by incomplete lineage sorting of ancestral alleles. In summary, ncOrtho allows to routinely consider miRNAs in evolutionary analyses that were thus far reserved to protein-coding genes.

Genome sequence and salinity adaptation of the desert shrub Nitraria sibirica (Nitrariaceae, Sapindales)

The genetic bases of halophytes for salinity tolerance are crucial for genetically breeding salt-tolerant crops. All natural Nitrariaceae species that exclusively occur in arid environments are highly tolerant to salt stress, but the underlying genomic bases to this adaptation remain unknown. Here we present a high-quality, chromosome-level genome sequence of Nitraria sibirica, with an assembled size of 456.66Mb and 23,365 annotated genes. Phylogenomic analyses confirmed N. sibirica as the sister to all other sampled representatives from other families in Sapindales, and no lineage-specific whole-genome duplication was found except the gamma triplication event. Still, we found that the genes involved in K + retention, energy supply, and Fe absorption expanded greatly in N. sibirica. Deep transcriptome analyses showed that leaf photosynthesis and cuticular wax formation in roots were enhanced under salt treatments. Furthermore, many transcription factors involved in salt tolerance changed their expressions significantly and displayed tissue- and concentration-dependent signaling in response to salt stress. Additionally, we found vacuolar Na + compartmentalization is an ongoing process under salt treatment, while Na + exclusion tends to function at high salt concentrations. These genomic and transcriptomic changes conferred salt tolerance in N. sibirica and pave the way for future breeding of salt-tolerant crops.

The genome sequence and demographic history of Przewalskia tangutica (Solanaceae), an endangered alpine plant on the Qinghai-Tibet Plateau.

To adapt to high-altitude habitats, many alpine plants develop self-compatible breeding systems from outcrossing. The genetic bases for this shift and the resulting demographic consequences remain largely unexplored. Here, we present a high-quality, chromosome-level genome assembly of the monotypic and endangered alpine perennial Przewalskia tangutica (Solanaceae) occurring on the Qinghai-Tibet Plateau (QTP). Our assembled genome is approximately 3 Gb, with a contig N50 size of 17 Mb, and we identified one lineage-specific whole-genome duplication. We found that the gametophytic self-incompatibility (GSI) syntenic locus to the other obligate outcrossing Solanaceae species was broken by the inserted the long terminal repeats, and changes in the flower-specific expression of the homologous genes, and the linked GSI genes in this species. Such changes may have led to its self-compatibility. We identified three deeply diverged lineages in the central distribution of this species, and the gene flow between them was weak but continuous. All three lineages diverged and decreased their population sizes since the largest glaciations occurred in the QTP approximately 720-500 thousand years ago. In addition, we identified one obvious hybrid population between two lineages, suggesting that genetic exchanges between and within lineages still occur. Our results provide insights into evolutionary adaptation through facultative self-pollination and demographic consequences of this alpine rare species in arid habitats.

Origin and Evolution of Marsupial-specific Imprinting Clusters Through Lineage-specific Gene Duplications and Acquisition of Promoter Differential Methylation.

Genomic imprinting is a parent-of-origin-specific expression phenomenon that plays fundamental roles in many biological processes. In animals, imprinting is only observed in therian mammals, with ∼200 imprinted genes known in humans and mice. The imprinting pattern in marsupials has been minimally investigated by examining orthologs to known eutherian imprinted genes. To identify marsupial-specific imprinting in an unbiased way, we performed RNA-seq studies on samples of fetal brain and placenta from the reciprocal cross progeny of two laboratory opossum stocks. We inferred allele-specific expression for >3,000 expressed genes and discovered/validated 13 imprinted genes, including three previously known imprinted genes, Igf2r, Peg10, and H19. We estimate that marsupials imprint ∼60 autosomal genes, which is a much smaller set compared with eutherians. Among the nine novel imprinted genes, three noncoding RNAs have no known homologs in eutherian mammals, while the remaining genes have important functions in pluripotency, transcription regulation, nucleolar homeostasis, and neural differentiation. Methylation analyses at promoter CpG islands revealed differentially methylated regions in five of these marsupial-specific imprinted genes, suggesting that differential methylation is a common mechanism in the epigenetic regulation of marsupial imprinting. Clustering and co-regulation were observed at marsupial imprinting loci Pou5f3-Npdc1 and Nkrfl-Ipncr2, but eutherian-type multi-gene imprinting clusters were not detected. Also differing from eutherian mammals, the brain and placenta imprinting profiles are remarkably similar in opossums, presumably due to the shared origin of these organs from the trophectoderm. Our results contribute to a fuller understanding of the origin, evolution, and mechanisms of genomic imprinting in therian mammals.