Identifying Clusters of High Confidence Homologies in Multiple Sequence Alignments

Phylogenomics including new sequence data of phytoplankton-infecting chytrids reveals multiple independent lifestyle transitions across the phylum

Parasitism is the most common lifestyle on Earth and has emerged many times independently across the eukaryotic tree of life. It is frequently found among chytrids (Chytridiomycota), which are early-branching unicellular fungi that feed osmotrophically via rhizoids as saprotrophs or parasites. Chytrids are abundant in most aquatic and terrestrial environments and fulfil important ecosystem functions. As parasites, they can have significant impacts on host populations. They cause global amphibian declines and influence the Earth's carbon cycle by terminating algal blooms. To date, the evolution of parasitism within the chytrid phylum remains unclear due to the low phylogenetic resolution of rRNA genes for the early diversification of fungi, and because few parasitic lineages have been cultured and genomic data for parasites is scarce. Here, we combine transcriptomics, culture-independent single-cell genomics and a phylogenomic approach to overcome these limitations. We newly sequenced 29 parasitic taxa and combined these with existing data to provide a robust backbone topology for the diversification of Chytridiomycota. Our analyses reveal multiple independent lifestyle transitions between parasitism and saprotrophy among chytrids and multiple host shifts by parasites. Based on these results and the parasitic lifestyle of other early-branching holomycotan lineages, we hypothesise that the chytrid last common ancestor was a parasite of phytoplankton.

Phylogenomic analyses of ochrophytes (stramenopiles) with an emphasis on neglected lineages

Ochrophyta is a photosynthetic lineage that crowns the phylogenetic tree of stramenopiles, one of the major eukaryotic supergroups. Due to their ecological impact as a major primary producer, ochrophytes are relatively well-studied compared to the rest of the stramenopiles, yet their evolutionary relationships remain poorly understood. This is in part due to a number of missing lineages in large-scale multigene analyses, and an apparently rapid radiation leading to many short internodes between ochrophyte subgroups in the tree. These short internodes are also found across deep-branching lineages of stramenopiles with limited phylogenetic signal, leaving many relationships controversial overall. We have addressed this issue with other deep-branching stramenopiles recently, and now examine whether contentious relationships within the ochrophytes may be resolved with the help of filling in missing lineages in an updated phylogenomic dataset of ochrophytes, along with exploring various gene filtering criteria to identify the most phylogenetically informative genes. We generated ten new transcriptomes from various culture collections and a single-cell isolation from an environmental sample, added these to an existing phylogenomic dataset, and examined the effects of selecting genes with high phylogenetic signal or low phylogenetic noise. For some previously contentious relationships, we find a variety of analyses and gene filtering criteria consistently unite previously unstable groupings with strong statistical support. For example, we recovered a robust grouping of Eustigmatophyceae with Raphidophyceae-Phaeophyceae-Xanthophyceae while Olisthodiscophyceae formed a sister-lineage to Pinguiophyceae. Selecting genes with high phylogenetic signal or data quality recovered more stable topologies. Overall, we find that adding under-represented groups across different lineages is still crucial in resolving phylogenetic relationships, and discrete gene properties affect lineages of stramenopiles differently. This is something which may be explored to further our understanding of the molecular evolution of stramenopiles.

Strong mitonuclear discordance in the phylogeny of Neodermata and evolutionary rates of Polyopisthocotylea

The genomic evolution of Polyopisthocotylea remains poorly understood in comparison to the remaining three classes of Neodermata: Monopisthocotylea, Cestoda, and Trematoda. Moreover, the evolutionary sequence of major events in the phylogeny of Neodermata remains unresolved. Herein we sequenced the mitogenome and transcriptome of the polyopisthocotylean Diplorchis sp., and conducted comparative evolutionary analyses using nuclear (nDNA) and mitochondrial (mtDNA) genomic datasets of Neodermata. We found strong mitonuclear discordance in the phylogeny of Neodermata. Polyopisthocotylea exhibited striking mitonuclear discordance in relative evolutionary rates: the fastest-evolving mtDNA in Neodermata and a comparatively slowly-evolving nDNA genome. This was largely attributable to its very long stem branch in mtDNA topologies, not exhibited by the nDNA data. We found indications that the fast evolution of mitochondrial genomes of Polyopisthocotylea may be driven both by relaxed purifying selection pressures and elevated levels of directional selection. We identified mitochondria-associated genes encoded in the nuclear genome: they exhibited unique evolutionary rates, but not correlated with the evolutionary rate of mtDNA, and there is no evidence for compensatory evolution (they evolved slower than the rest of the genome). Finally, there appears to exist an exceptionally large (≈6.3 kb) nuclear mitochondrial DNA segment (numt) in the nuclear genome of newly sequenced Diplorchis sp. A 3'-end segment of the 16S rRNA gene encoded by the numt was expressed, suggesting that this gene acquired novel, regulatory functions after the transposition to the nuclear genome. In conclusion, Polyopisthocotylea appears to be the lineage with the fastest-evolving mtDNA sequences among all of Bilateria, but most of the substitutions were accumulated deep in the evolutionary history of this lineage. As the nuclear genome does not exhibit a similar pattern, the circumstances underpinning this evolutionary phenomenon remain a mystery.

Evolutionary and functional insights into the Ski2-like helicase family in Archaea: a comparison of Thermococcales ASH-Ski2 and Hel308 activities

RNA helicases perform essential housekeeping and regulatory functions in all domains of life by binding and unwinding RNA molecules. The Ski2-like proteins are primordial helicases that play an active role in eukaryotic RNA homeostasis pathways, with multiple homologs having specialized functions. The significance of the expansion and diversity of Ski2-like proteins in Archaea, the third domain of life, has not yet been established. Here, by studying the phylogenetic diversity of Ski2-like helicases among archaeal genomes and the enzymatic activities of those in Thermococcales, we provide further evidence of the function of this protein family in archaeal metabolism of nucleic acids. We show that, in the course of evolution, ASH-Ski2 and Hel308-Ski2, the two main groups of Ski2-like proteins, have diverged in their biological functions. Whereas Hel308 has been shown to mainly act on DNA, we show that ASH-Ski2, previously described to be associated with the 5'-3' aRNase J exonuclease, acts on RNA by supporting an efficient annealing activity, but also an RNA unwinding with a 3'-5' polarity. To gain insights into the function of Ski2, we also analyse the transcriptome of Thermococcus barophilus ΔASH-Ski2 mutant strain and provide evidence of the importance of ASH-Ski2 in cellular metabolism pathways related to translation.

Single cell transcriptomics reveals UAR codon reassignment in Palmarella salina (Metopida, Armophorea) and confirms Armophorida belongs to APM clade

Anaerobes have emerged in several major lineages of ciliates, but the number of independent transitions to anaerobiosis among ciliates is unknown. The APM clade (Armophorea, Muranotrichea, Parablepharismea) represents the largest clade of obligate anaerobes among ciliates and contains free-living marine and freshwater representatives as well as gut endobionts of animals. The evolution of APM group has only recently started getting attention, and our knowledge on its phylogeny and genetics is still limited to a fraction of taxa. While ciliates portray a wide array of alternatives to the standard genetic code across numerous classes, the APM ciliates were considered to be the largest group using exclusively standard nuclear genetic code. In this study, we present a pan-ciliate phylogenomic analysis with emphasis on the APM clade, bringing the first phylogenomic analysis of the family Tropidoatractidae (Armophorea) and confirming the position of Armophorida within Armophorea. We include five newly sequenced single cell transcriptomes from marine, freshwater, and endobiotic APM ciliates - Palmarella salina, Anteclevelandella constricta, Nyctotherus sp., Caenomorpha medusula, and Thigmothrix strigosa. We report the first discovery of an alternative nuclear genetic code among APM ciliates, used by Palmarella salina (Tropidoatractidae, Armophorea), but not by its close relative, Tropidoatractus sp., and provide a comparative analysis of stop codon identity and frequency indicating the precedency to the UAG codon loss/reassignment over the UAA codon reassignment in the specific ancestor of Palmarella. Comparative genomic and proteomic studies of this group may help explain the constraints that underlie UAR stop-to-sense reassignment, the most frequent type of alternative nuclear genetic code, not only in ciliates, but eukaryotes in general.

A histone demethylase links the loss of plasticity to nongenetic inheritance and morphological change

Plasticity is a widespread feature of development, enabling phenotypic change based on the environment. Although the evolutionary loss of plasticity has been linked both theoretically and empirically to increased rates of phenotypic diversification, molecular insights into how this process might unfold are generally lacking. Here, we show that a regulator of nongenetic inheritance links evolutionary loss of plasticity in nature to changes in plasticity and morphology as selected in the laboratory. Across nematodes of Diplogastridae, which ancestrally had a polyphenism, or discrete plasticity, in their feeding morphology, we use molecular evolutionary analyses to screen for change associated with independent losses of plasticity. Having inferred a set of ancestrally polyphenism-biased genes from phylogenetically informed gene-knockouts and gene-expression comparisons, selection signatures associated with plasticity's loss identify the histone H3K4 di/monodemethylase gene spr-5/LSD1/KDM1A. Manipulations of this gene affect both sensitivity and variation in plastic morphologies, and artificial selection of manipulated lines drive multigenerational shifts in these phenotypes. Our findings thus give mechanistic insight into how traits are modified as they traverse the continuum of greater to lesser environmental sensitivity.

Phosphate Limitation Responses in Marine Green Algae Are Linked to Reprogramming of the tRNA Epitranscriptome and Codon Usage Bias

Marine algae are central to global carbon fixation, and their productivity is dictated largely by resource availability. Reduced nutrient availability is predicted for vast oceanic regions as an outcome of climate change; however, there is much to learn regarding response mechanisms of the tiny picoplankton that thrive in these environments, especially eukaryotic phytoplankton. Here, we investigate responses of the picoeukaryote Micromonas commoda, a green alga found throughout subtropical and tropical oceans. Under shifting phosphate availability scenarios, transcriptomic analyses revealed altered expression of transfer RNA modification enzymes and biased codon usage of transcripts more abundant during phosphate-limiting versus phosphate-replete conditions, consistent with the role of transfer RNA modifications in regulating codon recognition. To associate the observed shift in the expression of the transfer RNA modification enzyme complement with the transfer RNAs encoded by M. commoda, we also determined the transfer RNA repertoire of this alga revealing potential targets of the modification enzymes. Codon usage bias was particularly pronounced in transcripts encoding proteins with direct roles in managing phosphate limitation and photosystem-associated proteins that have ill-characterized putative functions in "light stress." The observed codon usage bias corresponds to a proposed stress response mechanism in which the interplay between stress-induced changes in transfer RNA modifications and skewed codon usage in certain essential response genes drives preferential translation of the encoded proteins. Collectively, we expose a potential underlying mechanism for achieving growth under enhanced nutrient limitation that extends beyond the catalog of up- or downregulated protein-encoding genes to the cell biological controls that underpin acclimation to changing environmental conditions.

Incongruence in the phylogenomics era

Genome-scale data and the development of novel statistical phylogenetic approaches have greatly aided the reconstruction of a broad sketch of the tree of life and resolved many of its branches. However, incongruence - the inference of conflicting evolutionary histories - remains pervasive in phylogenomic data, hampering our ability to reconstruct and interpret the tree of life. Biological factors, such as incomplete lineage sorting, horizontal gene transfer, hybridization, introgression, recombination and convergent molecular evolution, can lead to gene phylogenies that differ from the species tree. In addition, analytical factors, including stochastic, systematic and treatment errors, can drive incongruence. Here, we review these factors, discuss methodological advances to identify and handle incongruence, and highlight avenues for future research.

The Utilization of Reference-Guided Assembly and In Silico Libraries Improves the Draft Genome of Clarias batrachus and Culter alburnus

Long-read sequencing technologies can generate highly contiguous genome assemblies compared to short-read methods. However, their higher cost often poses a significant barrier. To address this, we explore the utilization of mapping-based genome assembly and reference-guided assembly as cost-effective alternative approaches. We assess the efficacy of these approaches in improving the contiguity of Clarias batrachus and Culter alburnus draft genomes. Our findings demonstrate that employing an iterative mapping strategy leads to a reduction in assembly errors. Specifically, after three iterations, the Mismatches per 100 kbp value for the C. batrachus genome decreased from 2447.20 to 2432.67, reaching a minimum of 2422.67 after two iterations. Additionally, the N50 value for the C. batrachus genome increased from 362,143 to 1,315,126 bp, with a maximum of 1,315,403 bp after two iterations. Furthermore, we achieved Mismatches per 100 kbp values of 3.70 for the reference-guided assembly of C. batrachus and 0.34 for C. alburnus. Correspondingly, the N50 value for the C. batrachus and C. alburnus genomes increased from 362,143 bp and 3,686,385 bp to 2,026,888 bp and 43,735,735 bp, respectively. Finally, we successfully utilized the improved C. batrachus and C. alburnus genomes to compare genome studies using the combined approach of Ragout and Ragtag. Through a comprehensive comparative analysis of mapping-based and reference-guided genome assembly methods, we shed light on the specific contributions of reference-guided assembly in reducing assembly errors and improving assembly continuity and integrity. These advancements establish reference-guided assembly and the utilization of in silico libraries as a promising and suitable approach for comparative genomics studies.

Single-cell genomics reveals new rozellid lineages and supports their sister relationship to Microsporidia

The phylum Rozellomycota has been proposed for a group of early-branching holomycotan lineages representing obligate parasites and hyperparasites of zoosporic fungi, oomycotes or phytoplankton. Given their predominantly intracellular lifestyle, rozellids are typically known from environmental ribosomal DNA data, except for the well-studied Rozella species. To date, the phylogenetic relationship between rozellids and microsporidians (Microsporidia) is not fully understood and most reliable hypotheses are based on phylogenomic analyses that incorporate the only publicly available rozellid genome of Rozella allomycis. Here, we provide genomic data of three new rozellid lineages obtained by single-cell sequencing from environmental samples and show with a phylogenomic approach that rozellids form a monophyletic group that is sister to microsporidians, corroborating the previously proposed phylum Rozellomycota. Whereas no mitochondrial genes coding for the respiratory Complex I could be found, we discovered a gene coding for a nucleotide phosphate transporter in one of the three draft genomes. The scattered absence of Complex I genes and scattered presence of nucleotide transporter genes across diverse microsporidian and rozellid lineages suggest that these adaptations to a parasitic lifestyle, which reduce the parasite's capability to synthesize ATP but enables it to steal ATP from its host, evolved independently in microsporidians and rozellids.

PhylteR: Efficient Identification of Outlier Sequences in Phylogenomic Datasets

In phylogenomics, incongruences between gene trees, resulting from both artifactual and biological reasons, can decrease the signal-to-noise ratio and complicate species tree inference. The amount of data handled today in classical phylogenomic analyses precludes manual error detection and removal. However, a simple and efficient way to automate the identification of outliers from a collection of gene trees is still missing. Here, we present PhylteR, a method that allows rapid and accurate detection of outlier sequences in phylogenomic datasets, i.e. species from individual gene trees that do not follow the general trend. PhylteR relies on DISTATIS, an extension of multidimensional scaling to 3 dimensions to compare multiple distance matrices at once. In PhylteR, these distance matrices extracted from individual gene phylogenies represent evolutionary distances between species according to each gene. On simulated datasets, we show that PhylteR identifies outliers with more sensitivity and precision than a comparable existing method. We also show that PhylteR is not sensitive to ILS-induced incongruences, which is a desirable feature. On a biological dataset of 14,463 genes for 53 species previously assembled for Carnivora phylogenomics, we show (i) that PhylteR identifies as outliers sequences that can be considered as such by other means, and (ii) that the removal of these sequences improves the concordance between the gene trees and the species tree. Thanks to the generation of numerous graphical outputs, PhylteR also allows for the rapid and easy visual characterization of the dataset at hand, thus aiding in the precise identification of errors. PhylteR is distributed as an R package on CRAN and as containerized versions (docker and singularity).

Multiple parallel origins of parasitic Marine Alveolates

Microbial eukaryotes are important components of marine ecosystems, and the Marine Alveolates (MALVs) are consistently both abundant and diverse in global environmental sequencing surveys. MALVs are dinoflagellates that are thought to be parasites of other protists and animals, but the lack of data beyond ribosomal RNA gene sequences from all but a few described species means much of their biology and evolution remain unknown. Using single-cell transcriptomes from several MALVs and their free-living relatives, we show that MALVs evolved independently from two distinct, free-living ancestors and that their parasitism evolved in parallel. Phylogenomics shows one subgroup (MALV-II and -IV, or Syndiniales) is related to a novel lineage of free-living, eukaryovorous predators, the eleftherids, while the other (MALV-I, or Ichthyodinida) is related to the free-living predator Oxyrrhis and retains proteins targeted to a non-photosynthetic plastid. Reconstructing the evolution of photosynthesis, plastids, and parasitism in early-diverging dinoflagellates shows a number of parallels with the evolution of their apicomplexan sisters. In both groups, similar forms of parasitism evolved multiple times and photosynthesis was lost many times. By contrast, complete loss of the plastid organelle is infrequent and, when this does happen, leaves no residual genes.

The evolution of endoparasitism and complex life cycles in parasitic platyhelminths

Within flatworms, the vast majority of parasitism is innate to Neodermata, the most derived and diversified group of the phylum Platyhelminthes.1,2 The four major lineages of Neodermata maintain various combinations of life strategies.3 They include both externally (ecto-) and internally feeding (endo-) parasites. Some lineages complete their life cycles directly by infecting a single host, whereas others succeed only through serial infections of multiple hosts of various vertebrate and invertebrate groups. Food sources and modes of digestion add further combinatorial layers to the often incompletely understood mosaic of neodermatan life histories. Their evolutionary trajectories have remained molecularly unresolved because of conflicting evolutionary inferences and a lack of genomic data.4 Here, we generated transcriptomes for nine early branching neodermatan representatives and performed detailed phylogenomic analyses to address these critical gaps. Polyopisthocotylea, mostly hematophagous ectoparasites, form a group with the mostly hematophagous but endoparasitic trematodes (Trematoda), rather than sharing a common ancestor with Monopisthocotylea, ectoparasitic epithelial feeders. Phylogenetic placement of the highly specialized endoparasitic Cestoda alters depending on the model. Regardless of this uncertainty, this study brings an unconventional perspective on the evolution of platyhelminth parasitism, rejecting a common origin for the endoparasitic lifestyle intrinsic to cestodes and trematodes. Instead, our data indicate that complex life cycles and invasion of vertebrates' gut lumen, the hallmark features of these parasites, evolved independently within Neodermata. We propose the demise of the traditionally recognized class Monogenea and the promotion of its two subclasses to the class level as Monopisthocotyla new class and Polyopisthocotyla new class.

Genomic Signatures Associated with Transitions to Viviparity in Cyprinodontiformes

The transition from oviparity to viviparity has occurred independently over 150 times across vertebrates, presenting one of the most compelling cases of phenotypic convergence. However, whether the repeated, independent evolution of viviparity is driven by redeployment of similar genetic mechanisms and whether these leave a common signature in genomic divergence remains largely unknown. Although recent investigations into the evolution of viviparity have demonstrated striking similarity among the genes and molecular pathways involved across disparate vertebrate groups, quantitative tests for genome-wide convergent have provided ambivalent answers. Here, we investigate the potential role of molecular convergence during independent transitions to viviparity across an order of ray-finned freshwater fish (Cyprinodontiformes). We assembled de novo genomes and utilized publicly available genomes of viviparous and oviparous species to test for molecular convergence across both coding and noncoding regions. We found no evidence for an excess of molecular convergence in amino acid substitutions and in rates of sequence divergence, implying independent genetic changes are associated with these transitions. However, both statistical power and biological confounds could constrain our ability to detect significant correlated evolution. We therefore identified candidate genes with potential signatures of molecular convergence in viviparous Cyprinodontiformes lineages. Motif enrichment and gene ontology analyses suggest transcriptional changes associated with early morphogenesis, brain development, and immunity occurred alongside the evolution of viviparity. Overall, however, our findings indicate that independent transitions to viviparity in these fish are not strongly associated with an excess of molecular convergence, but a few genes show convincing evidence of convergent evolution.

Extensive mitogenomic heteroplasmy and its implications in the phylogeny of the fish genus Megalobrama

Megalobrama is China's most economically valuable fish genera. Four species make up this genus: M. amblycephala (MA), M. terminalis (MT), M. pellegrini (MP), and M. hoffmanni (MH). Many researchers have investigated the genetic relationship of Megalobrama based on mitochondrial DNA (mtDNA) and discovered that the branches of the phylogenetic tree for MT and MP are intertwined. We hypothesized that this occurs because mitogenomic heteroplasmy is overlooked when working with mtDNA, which causes MP and MT positions to intersect in phylogenetic trees. To eliminate the influence of nuclear mitochondrial DNA fragments (NUMTs) before analyzing mitogenomic heteroplasmy, we used PLastZ to identify NUMTs, which were then removed from the samples for the subsequent heteroplasmy analysis. Using the heteroplasmy caller icHET, we discovered 126, 339, 135, and 203 heteroplasmic variants in six MA, MT, MP, and MH samples. We reconstructed the Megalobrama fish genus's phylogenetic tree using the RY coding method and rejecting the third position on codons, which improved the performance of the phylogenetic tree by increasing the ratio of treeness to relative component variability from 100.02 ± 1.76 to 688.59 ± 190.56. Despite this, the RY coding method cannot alter the intersection of MP and MT positions in phylogenetic trees. We hypothesize that gene flow between MT and MP leads to intertwining mtDNA-based phylogenetic trees. In conclusion, our findings on the mitogenomic heteroplasmy of Megalobrama provide new insights into mtDNA-based phylogenetic studies.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03523-0.

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

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

Identification of a TonB-Dependent Receptor Involved in Lanthanide Switch by the Characterization of Laboratory-Adapted Methylosinus trichosporium OB3b

Two methanol dehydrogenases (MDHs), MxaFI and XoxF, have been characterized in methylotrophic and methanotrophic bacteria. MxaFI contains a calcium ion in its active site, whereas XoxF contains a lanthanide ion. Importantly, the expression of MxaFI and XoxF is inversely regulated by lanthanide bioavailability, i.e., the "lanthanide switch." To reveal the genetic and environmental factors affecting the lanthanide switch, we focused on two Methylosinus trichosporium OB3b mutants isolated during routine cultivation. In these mutants, MxaF was constitutively expressed, but lanthanide-dependent XoxF1 was not, even in the presence of 25 μM cerium ions, which is sufficient for XoxF expression in the wild type. Genotyping showed that both mutants harbored a loss-of-function mutation in the CQW49_RS02145 gene, which encodes a TonB-dependent receptor. Gene disruption and complementation experiments demonstrated that CQW49_RS02145 was required for XoxF1 expression in the presence of 25 μM cerium ions. Phylogenetic analysis indicated that CQW49_RS02145 was homologous to the Methylorubrum extorquens AM1 lanthanide transporter gene (lutH). These findings suggest that CQW49_RS02145 is involved in lanthanide uptake across the outer membrane. Furthermore, we demonstrated that supplementation with cerium and glycerol caused severe growth arrest in the wild type. CQW49_RS02145 underwent adaptive laboratory evolution in the presence of cerium and glycerol ions, resulting in a mutation that partially mitigated the growth arrest. This finding implies that loss-of-function mutations in CQW49_RS02145 can be attributed to residual glycerol from the frozen stock. IMPORTANCE Lanthanides are widely used in many industrial applications, including catalysts, magnets, and polishing. Recently, lanthanide-dependent metabolism was characterized in methane-utilizing bacteria. Despite the global demand for lanthanides, few studies have investigated the mechanism of lanthanide uptake by these bacteria. In this study, we identify a lanthanide transporter in Methylosinus trichosporium OB3b and indicate the potential interaction between intracellular lanthanide and glycerol. Understanding the genetic and environmental factors affecting lanthanide uptake should not only help improve the use of lanthanides for the bioconversion of methane into valuable products like methanol but also be of value for developing biomining to extract lanthanides under neutral conditions.

Integrating Phylogenetics With Intron Positions Illuminates the Origin of the Complex Spliceosome

Eukaryotic genes are characterized by the presence of introns that are removed from pre-mRNA by a spliceosome. This ribonucleoprotein complex is comprised of multiple RNA molecules and over a hundred proteins, which makes it one of the most complex molecular machines that originated during the prokaryote-to-eukaryote transition. Previous works have established that these introns and the spliceosomal core originated from self-splicing introns in prokaryotes. Yet, how the spliceosomal core expanded by recruiting many additional proteins remains largely elusive. In this study, we use phylogenetic analyses to infer the evolutionary history of 145 proteins that we could trace back to the spliceosome in the last eukaryotic common ancestor. We found that an overabundance of proteins derived from ribosome-related processes was added to the prokaryote-derived core. Extensive duplications of these proteins substantially increased the complexity of the emerging spliceosome. By comparing the intron positions between spliceosomal paralogs, we infer that most spliceosomal complexity postdates the spread of introns through the proto-eukaryotic genome. The reconstruction of early spliceosomal evolution provides insight into the driving forces behind the emergence of complexes with many proteins during eukaryogenesis.

Reconstruction of Plastid Proteomes of Apicomplexans and Close Relatives Reveals the Major Evolutionary Outcomes of Cryptic Plastids

Apicomplexans and related lineages comprise many obligate symbionts of animals; some of which cause notorious diseases such as malaria. They evolved from photosynthetic ancestors and transitioned into a symbiotic lifestyle several times, giving rise to species with diverse non-photosynthetic plastids. Here, we sought to reconstruct the evolution of the cryptic plastids in the apicomplexans, chrompodellids, and squirmids (ACS clade) by generating five new single-cell transcriptomes from understudied gregarine lineages, constructing a robust phylogenomic tree incorporating all ACS clade sequencing datasets available, and using these to examine in detail, the evolutionary distribution of all 162 proteins recently shown to be in the apicoplast by spatial proteomics in Toxoplasma. This expanded homology-based reconstruction of plastid proteins found in the ACS clade confirms earlier work showing convergence in the overall metabolic pathways retained once photosynthesis is lost, but also reveals differences in the degrees of plastid reduction in specific lineages. We show that the loss of the plastid genome is common and unexpectedly find many lineage- and species-specific plastid proteins, suggesting the presence of evolutionary innovations and neofunctionalizations that may confer new functional and metabolic capabilities that are yet to be discovered in these enigmatic organelles.

Viral origin of eukaryotic type IIA DNA topoisomerases

Type II DNA topoisomerases of the family A (Topo IIAs) are present in all Bacteria (DNA gyrase) and eukaryotes. In eukaryotes, they play a major role in transcription, DNA replication, chromosome segregation, and modulation of chromosome architecture. The origin of eukaryotic Topo IIA remains mysterious since they are very divergent from their bacterial homologs and have no orthologs in Archaea. Interestingly, eukaryotic Topo IIAs have close homologs in viruses of the phylum Nucleocytoviricota, an expansive assemblage of large and giant viruses formerly known as the nucleocytoplasmic large DNA viruses. Topo IIAs are also encoded by some bacterioviruses of the class Caudoviricetes (tailed bacteriophages). To elucidate the origin of the eukaryotic Topo IIA, we performed in-depth phylogenetic analyses on a dataset combining viral and cellular Topo IIA homologs. Topo IIAs encoded by Bacteria and eukaryotes form two monophyletic groups nested within Topo IIA encoded by Caudoviricetes and Nucleocytoviricota, respectively. Importantly, Nucleocytoviricota remained well separated from eukaryotes after removing both Bacteria and Caudoviricetes from the data set, indicating that the separation of Nucleocytoviricota and eukaryotes is probably not due to long-branch attraction artifact. The topologies of our trees suggest that the eukaryotic Topo IIA was probably acquired from an ancestral member of the Nucleocytoviricota of the class Megaviricetes, before the emergence of the last eukaryotic common ancestor (LECA). This result further highlights a key role of these viruses in eukaryogenesis and suggests that early proto-eukaryotes used a Topo IIB instead of a Topo IIA for solving their DNA topological problems.

NeoRdRp: A Comprehensive Dataset for Identifying RNA-dependent RNA Polymerases of Various RNA Viruses from Metatranscriptomic Data

RNA viruses are distributed throughout various environments, and most have recently been identified by metatranscriptome sequencing. However, due to the high nucleotide diversity of RNA viruses, it is still challenging to identify novel RNA viruses from metatranscriptome data. To overcome this issue, we created a dataset of RNA-dependent RNA polymerase (RdRp) domains that are essential for all RNA viruses belonging to Orthornavirae. Genes with RdRp domains from various RNA viruses were clustered based on amino acid sequence similarities. A multiple sequence alignment was generated for each cluster, and a hidden Markov model (HMM) profile was created when the number of sequences was greater than three. We further refined 426 HMM profiles by detecting RefSeq RNA virus sequences and subsequently combined the hit sequences with the RdRp domains. As a result, 1,182 HMM profiles were generated from 12,502 RdRp domain sequences, and the dataset was named NeoRdRp. The majority of NeoRdRp HMM profiles successfully detected RdRp domains, specifically in the UniProt dataset. Furthermore, we compared the NeoRdRp dataset with two previously reported methods for RNA virus detection using metatranscriptome sequencing data. Our methods successfully identified the majority of RNA viruses in the datasets; however, some RNA viruses were not detected, similar to the other two methods. NeoRdRp may be repeatedly improved by the addition of new RdRp sequences and is applicable as a system for detecting various RNA viruses from diverse metatranscriptome data.

The Gluopsins: Opsins without the Retinal Binding Lysine

Opsins allow us to see. They are G-protein-coupled receptors and bind as ligand retinal, which is bound covalently to a lysine in the seventh transmembrane domain. This makes opsins light-sensitive. The lysine is so conserved that it is used to define a sequence as an opsin and thus phylogenetic opsin reconstructions discard any sequence without it. However, recently, opsins were found that function not only as photoreceptors but also as chemoreceptors. For chemoreception, the lysine is not needed. Therefore, we wondered: Do opsins exists that have lost this lysine during evolution? To find such opsins, we built an automatic pipeline for reconstructing a large-scale opsin phylogeny. The pipeline compiles and aligns sequences from public sources, reconstructs the phylogeny, prunes rogue sequences, and visualizes the resulting tree. Our final opsin phylogeny is the largest to date with 4956 opsins. Among them is a clade of 33 opsins that have the lysine replaced by glutamic acid. Thus, we call them gluopsins. The gluopsins are mainly dragonfly and butterfly opsins, closely related to the RGR-opsins and the retinochromes. Like those, they have a derived NPxxY motif. However, what their particular function is, remains to be seen.

The evolutionary origin of host association in the Rickettsiales

The evolution of obligate host-association of bacterial symbionts and pathogens remains poorly understood. The Rickettsiales are an alphaproteobacterial order of obligate endosymbionts and parasites that infect a wide variety of eukaryotic hosts, including humans, livestock, insects and protists. Induced by their host-associated lifestyle, Rickettsiales genomes have undergone reductive evolution, leading to small, AT-rich genomes with limited metabolic capacities. Here we uncover eleven deep-branching alphaproteobacterial metagenome assembled genomes from aquatic environments, including data from the Tara Oceans initiative and other publicly available datasets, distributed over three previously undescribed Rickettsiales-related clades. Phylogenomic analyses reveal that two of these clades, Mitibacteraceae and Athabascaceae, branch sister to all previously sampled Rickettsiales. The third clade, Gamibacteraceae, branch sister to the recently identified ectosymbiotic ‘Candidatus Deianiraea vastatrix’. Comparative analyses indicate that the gene complement of Mitibacteraceae and Athabascaceae is reminiscent of that of free-living and biofilm-associated bacteria. Ancestral genome content reconstruction across the Rickettsiales species tree further suggests that the evolution of host association in Rickettsiales was a gradual process that may have involved the repurposing of a type IV secretion system.

Phylogenomic analyses reveal novel environmental clades of Rickettsiales providing insights into their evolution from free-living to host-associated lifestyle.

Marine gregarine genomes reveal the breadth of apicomplexan diversity with a partially conserved glideosome machinery

Our current view of the evolutionary history, coding and adaptive capacities of Apicomplexa, protozoan parasites of a wide range of metazoan, is currently strongly biased toward species infecting humans, as data on early diverging apicomplexan lineages infecting invertebrates is extremely limited. Here, we characterized the genome of the marine eugregarine Porospora gigantea, intestinal parasite of Lobsters, remarkable for the macroscopic size of its vegetative feeding forms (trophozoites) and its gliding speed, the fastest so far recorded for Apicomplexa. Two highly syntenic genomes named A and B were assembled. Similar in size (~ 9 Mb) and coding capacity (~ 5300 genes), A and B genomes are 10.8% divergent at the nucleotide level, corresponding to 16-38 My in divergent time. Orthogroup analysis across 25 (proto)Apicomplexa species, including Gregarina niphandrodes, showed that A and B are highly divergent from all other known apicomplexan species, revealing an unexpected breadth of diversity. Phylogenetically these two species branch sisters to Cephaloidophoroidea, and thus expand the known crustacean gregarine superfamily. The genomes were mined for genes encoding proteins necessary for gliding, a key feature of apicomplexans parasites, currently studied through the molecular model called glideosome. Sequence analysis shows that actin-related proteins and regulatory factors are strongly conserved within apicomplexans. In contrast, the predicted protein sequences of core glideosome proteins and adhesion proteins are highly variable among apicomplexan lineages, especially in gregarines. These results confirm the importance of studying gregarines to widen our biological and evolutionary view of apicomplexan species diversity, and to deepen our understanding of the molecular bases of key functions such as gliding, well known to allow access to the intracellular parasitic lifestyle in Apicomplexa.

Phylogenomic insights into the early diversification of fungi

Phylogenomic analyses have boosted our understanding of the evolutionary trajectories of all living forms by providing continuous improvements to the tree of life.^1-5 Within this tree, fungi represent an ancient eukaryote group,⁶ having diverged from the animals ∼1.35 billion years ago.⁷ Estimates of the number of extant species range between 1.5 and 3.8 million.^8,9 Recent reclassifications and the discovery of the deep-branching Sanchytriomycota lineage¹⁰ have brought the number of proposed phyla to 20,¹¹ 21 if the Microsporidia are included.^12-14 Uncovering how the diverse and globally distributed fungi are related to each other is fundamental for understanding how their lifestyles, morphologies, and metabolic capacities evolved. To date, many of the proposed relationships among the phyla remain controversial and no phylogenomic study has examined the entire fungal tree using a taxonomically comprehensive dataset and suitable models of evolution. We assembled and curated a 299-protein dataset with a taxon sampling broad enough to encompass all recognized fungal diversity with available data, but selective enough to run computationally intensive analyses using best-fitting models. Using a range of reconstruction methods, we were able to resolve many contested nodes, such as a sister relationship of Chytridiomyceta to all other non-Opisthosporidia fungi (with Chytridiomycota being sister to Monoblepharomycota + Neocallimastigomycota), a branching of Blastocladiomycota + Sanchytriomycota after the Chytridiomyceta but before other non-Opisthosporidia fungi, and a branching of Glomeromycota as sister to the Dikarya. Our up-to-date fungal tree of life will serve as a springboard for future investigations on the early evolution of fungi.

Site-and-branch-heterogeneous analyses of an expanded dataset favour mitochondria as sister to known Alphaproteobacteria

Determining the phylogenetic origin of mitochondria is key to understanding the ancestral mitochondrial symbiosis and its role in eukaryogenesis. However, the precise evolutionary relationship between mitochondria and their closest bacterial relatives remains hotly debated. The reasons include pervasive phylogenetic artefacts as well as limited protein and taxon sampling. Here we developed a new model of protein evolution that accommodates both across-site and across-branch compositional heterogeneity. We applied this site-and-branch-heterogeneous model (MAM60 + GFmix) to a considerably expanded dataset that comprises 108 mitochondrial proteins of alphaproteobacterial origin, and novel metagenome-assembled genomes from microbial mats, microbialites and sediments. The MAM60 + GFmix model fits the data much better and agrees with analyses of compositionally homogenized datasets with conventional site-heterogenous models. The consilience of evidence thus suggests that mitochondria are sister to the Alphaproteobacteria to the exclusion of MarineProteo1 and Magnetococcia. We also show that the ancestral presence of the crista-developing mitochondrial contact site and cristae organizing system (a mitofilin-domain-containing Mic60 protein) in mitochondria and the Alphaproteobacteria only supports their close relationship.

The complete chloroplast genome sequence of Athrotaxis cupressoides

Athrotaxis cupressoides (Cupressaceae) is a Tasmanian endemic conifer. It is mainly threatened by habitat fragmentation and limited distribution, yet little is known about its genomic background. In this study, the complete chloroplast (cp) genome of the species was assembled and annotated. The cp genome of A. cupressoides is a circular of 134,248 bp in size, where the inverted repeat regions (IRs) were lost. A total of 112 unique genes were annotated, including 78 proteins-coding genes, four rRNA genes, and 30 tRNA genes. The maximum likelihood (ML) phylogenetic tree indicates that the subfamily Athrotaxidoideae, to which A. cupressoides belongs, is sister to a clade including four subfamilies including Sequoioideae, Taxodioideae, Cupressoideae, and Callitroideae. The complete cp genome will be helpful to further studies on the conservation of this species and the evolutionary history of Cupressaceae.

Single cell genomics reveals plastid-lacking Picozoa are close relatives of red algae

The endosymbiotic origin of plastids from cyanobacteria gave eukaryotes photosynthetic capabilities and launched the diversification of countless forms of algae. These primary plastids are found in members of the eukaryotic supergroup Archaeplastida. All known archaeplastids still retain some form of primary plastids, which are widely assumed to have a single origin. Here, we use single-cell genomics from natural samples combined with phylogenomics to infer the evolutionary origin of the phylum Picozoa, a globally distributed but seemingly rare group of marine microbial heterotrophic eukaryotes. Strikingly, the analysis of 43 single-cell genomes shows that Picozoa belong to Archaeplastida, specifically related to red algae and the phagotrophic rhodelphids. These picozoan genomes support the hypothesis that Picozoa lack a plastid, and further reveal no evidence of an early cryptic endosymbiosis with cyanobacteria. These findings change our understanding of plastid evolution as they either represent the first complete plastid loss in a free-living taxon, or indicate that red algae and rhodelphids obtained their plastids independently of other archaeplastids.

Next-generation sequencing reveals the mitogenomic heteroplasmy in the topmouth culter (Culter alburnus Basilewsky, 1855)

BACKGROUND

The mitogenomic heteroplasmy is the presence of multiple haplotypes in the mitochondria, which could cause genetic diseases and is also associated with many critical biological functions. The topmouth culter (Culter alburnus Basilewsky, 1855) is one of the most important freshwater fish in the family of Cyprinidae in China. At present, there are no reports on the topmouth culter's mtDNA heteroplasmy and the existence of which is not known.

METHODS AND RESULTS

This study aimed to analyze the mitogenomic heteroplasmy in the topmouth culter by the next-generation sequencing of the fins' total DNA. The results confirmed the existence of the heteroplasmy and indicated the presence of the extensive heteroplasmy in the topmouth culter's mitogenome. There were 38 heteroplasmic variations in the protein-coding genes from the three specimens, with 33 non-synonymous substitutions accounting for 86.84% and five synonymous substitutions accounting for 13.16%. Among them, the ND6 had the most heteroplasmic variations but only one synonymous substitution. After removing the putative nuclear mitochondrial DNA fragments, the ratio of primary haplotype in the three specimens was 43.89%, 74.72%, and 32.76%, respectively. The three specimens contained 21, 7, and 21 haplotypes of the mitogenomes, respectively. Due to the extensive heteroplasmy, we reconstructed the phylogenetic tree of the topmouth culter using the RY-coding method, which improved the performance of the phylogenetic tree to some extent.

CONCLUSIONS

This study reported the mitogenomic heteroplasmy in the topmouth culter and enhanced the knowledge regarding the mitogenomic heteroplasmy in phylogenetic studies. As the topmouth culter is a commercial species, the mitogenomic heteroplasmy is crucial for the fisheries management of the topmouth culter.

Plastid phylogenomics of the Gynoxoid group (Senecioneae, Asteraceae) highlights the importance of motif-based sequence alignment amid low genetic distances

PREMISE

The genus Gynoxys and relatives form a species-rich lineage of Andean shrubs and trees with low genetic distances within the sunflower subtribe Tussilaginineae. Previous molecular phylogenetic investigations of the Tussilaginineae have included few, if any, representatives of this Gynoxoid group or reconstructed ambiguous patterns of relationships for it.

METHODS

We sequenced complete plastid genomes of 21 species of the Gynoxoid group and related Tussilaginineae and conducted detailed comparisons of the phylogenetic relationships supported by the gene, intron, and intergenic spacer partitions of these genomes. We also evaluated the impact of manual, motif-based adjustments of automatic DNA sequence alignments on phylogenetic tree inference.

RESULTS

Our results indicate that the inclusion of all plastid genome partitions is needed to infer well-supported phylogenetic trees of the Gynoxoid group. Whole plastome-based tree inference suggests that the genera Gynoxys and Nordenstamia are polyphyletic and form the core clade of the Gynoxoid group. This clade is sister to a clade of Aequatorium and Paragynoxys and also includes some but not all representatives of Paracalia.

CONCLUSIONS

The concatenation and combined analysis of all plastid genome partitions and the construction of manually-curated, motif-based DNA sequence alignments are found to be instrumental in the recovery of well-supported relationships of the Gynoxoid group. We demonstrate that the correct assessment of homology in genome-level plastid sequence data sets is crucial for subsequent phylogeny reconstruction and that the manual post-processing of multiple sequence alignments improves the reliability of such reconstructions amid low genetic distances between taxa.

Anaeramoebae are a divergent lineage of eukaryotes that shed light on the transition from anaerobic mitochondria to hydrogenosomes

Discoveries of diverse microbial eukaryotes and their inclusion in comprehensive phylogenomic analyses have crucially re-shaped the eukaryotic tree of life in the 21st century.¹ At the deepest level, eukaryotic diversity comprises 9-10 "supergroups." One of these supergroups, the Metamonada, is particularly important to our understanding of the evolutionary dynamics of eukaryotic cells, including the remodeling of mitochondrial function. All metamonads thrive in low-oxygen environments and lack classical aerobic mitochondria, instead possessing mitochondrion-related organelles (MROs) with metabolisms that are adapted to low-oxygen conditions. These MROs lack an organellar genome, do not participate in the Krebs cycle and oxidative phosphorylation,² and often synthesize ATP by substrate-level phosphorylation coupled to hydrogen production.^3,4 The events that occurred during the transition from an oxygen-respiring mitochondrion to a functionally streamlined MRO early in metamonad evolution remain largely unknown. Here, we report transcriptomes of two recently described, enigmatic, anaerobic protists from the genus Anaeramoeba.⁵ Using phylogenomic analysis, we show that these species represent a divergent, phylum-level lineage in the tree of metamonads, emerging as a sister group of the Parabasalia and reordering the deep branching order of the metamonad tree. Metabolic reconstructions of the Anaeramoeba MROs reveal many "classical" mitochondrial features previously not seen in metamonads, including a disulfide relay import system, propionate production, and amino acid metabolism. Our findings suggest that the cenancestor of Metamonada likely had MROs with more classical mitochondrial features than previously anticipated and demonstrate how discoveries of novel lineages of high taxonomic rank continue to transform our understanding of early eukaryote evolution.

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.

PhyloFisher: A phylogenomic package for resolving eukaryotic relationships

Phylogenomic analyses of hundreds of protein-coding genes aimed at resolving phylogenetic relationships is now a common practice. However, no software currently exists that includes tools for dataset construction and subsequent analysis with diverse validation strategies to assess robustness. Furthermore, there are no publicly available high-quality curated databases designed to assess deep (>100 million years) relationships in the tree of eukaryotes. To address these issues, we developed an easy-to-use software package, PhyloFisher (https://github.com/TheBrownLab/PhyloFisher), written in Python 3. PhyloFisher includes a manually curated database of 240 protein-coding genes from 304 eukaryotic taxa covering known eukaryotic diversity, a novel tool for ortholog selection, and utilities that will perform diverse analyses required by state-of-the-art phylogenomic investigations. Through phylogenetic reconstructions of the tree of eukaryotes and of the Saccharomycetaceae clade of budding yeasts, we demonstrate the utility of the PhyloFisher workflow and the provided starting database to address phylogenetic questions across a large range of evolutionary time points for diverse groups of organisms. We also demonstrate that undetected paralogy can remain in phylogenomic "single-copy orthogroup" datasets constructed using widely accepted methods such as all vs. all BLAST searches followed by Markov Cluster Algorithm (MCL) clustering and application of automated tree pruning algorithms. Finally, we show how the PhyloFisher workflow helps detect inadvertent paralog inclusions, allowing the user to make more informed decisions regarding orthology assignments, leading to a more accurate final dataset.

Build a better bootstrap and the RAWR shall beat a random path to your door: phylogenetic support estimation revisited

Motivation

The standard bootstrap method is used throughout science and engineering to perform general-purpose non-parametric resampling and re-estimation. Among the most widely cited and widely used such applications is the phylogenetic bootstrap method, which Felsenstein proposed in 1985 as a means to place statistical confidence intervals on an estimated phylogeny (or estimate ‘phylogenetic support’). A key simplifying assumption of the bootstrap method is that input data are independent and identically distributed (i.i.d.). However, the i.i.d. assumption is an over-simplification for biomolecular sequence analysis, as Felsenstein noted.

Results

In this study, we introduce a new sequence-aware non-parametric resampling technique, which we refer to as RAWR (‘RAndom Walk Resampling’). RAWR consists of random walks that synthesize and extend the standard bootstrap method and the ‘mirrored inputs’ idea of Landan and Graur. We apply RAWR to the task of phylogenetic support estimation. RAWR’s performance is compared to the state-of-the-art using synthetic and empirical data that span a range of dataset sizes and evolutionary divergence. We show that RAWR support estimates offer comparable or typically superior type I and type II error compared to phylogenetic bootstrap support. We also conduct a re-analysis of large-scale genomic sequence data from a recent study of Darwin’s finches. Our findings clarify phylogenetic uncertainty in a charismatic clade that serves as an important model for complex adaptive evolution.

Availability and implementation

Data and software are publicly available under open-source software and open data licenses at: https://gitlab.msu.edu/liulab/RAWR-study-datasets-and-scripts.

A standardized archaeal taxonomy for the Genome Taxonomy Database

The accrual of genomic data from both cultured and uncultured microorganisms provides new opportunities to develop systematic taxonomies based on evolutionary relationships. Previously, we established a bacterial taxonomy through the Genome Taxonomy Database. Here, we propose a standardized archaeal taxonomy that is derived from a 122-concatenated-protein phylogeny that resolves polyphyletic groups and normalizes ranks based on relative evolutionary divergence. The resulting archaeal taxonomy, which forms part of the Genome Taxonomy Database, is stable for a range of phylogenetic variables including marker gene selection, inference methods, corrections for rate heterogeneity and compositional bias, tree rooting scenarios and expansion of the genome database. Rank normalization is shown to robustly correct for substitution rates varying up to 30-fold using simulated datasets. Taxonomic curation follows the rules of the International Code of Nomenclature of Prokaryotes while taking into account proposals to formally recognize the rank of phylum and to use genome sequences as type material. This taxonomy is based on 2,392 archaeal genomes, 93.3% of which required one or more changes to their existing taxonomy, mainly owing to incomplete classification. We identify 16 archaeal phyla and reclassify 3 major monophyletic units from the former Euryarchaeota and one phylum that unites the Thaumarchaeota-Aigarchaeota-Crenarchaeota-Korarchaeota (TACK) superphylum into a single phylum.

Recoding of stop codons expands the metabolic potential of two novel Asgardarchaeota lineages

Asgardarchaeota have been proposed as the closest living relatives to eukaryotes, and a total of 72 metagenome-assembled genomes (MAGs) representing six primary lineages in this archaeal phylum have thus far been described. These organisms are predicted to be fermentative heterotrophs contributing to carbon cycling in sediment ecosystems. Here, we double the genomic catalogue of Asgardarchaeota by obtaining 71 MAGs from a range of habitats around the globe, including the deep subsurface, brackish shallow lakes, and geothermal spring sediments. Phylogenomic inferences followed by taxonomic rank normalisation confirmed previously established Asgardarchaeota classes and revealed four additional lineages, two of which were consistently recovered as monophyletic classes. We therefore propose the names Candidatus Sifarchaeia class nov. and Ca. Jordarchaeia class nov., derived from the gods Sif and Jord in Norse mythology. Metabolic inference suggests that both classes represent hetero-organotrophic acetogens, which also have the ability to utilise methyl groups such as methylated amines, with acetate as the probable end product in remnants of a methanogen-derived core metabolism. This inferred mode of energy conservation is predicted to be enhanced by genetic code expansions, i.e., stop codon recoding, allowing the incorporation of the rare 21st and 22nd amino acids selenocysteine (Sec) and pyrrolysine (Pyl). We found Sec recoding in Jordarchaeia and all other Asgardarchaeota classes, which likely benefit from increased catalytic activities of Sec-containing enzymes. Pyl recoding, on the other hand, is restricted to Sifarchaeia in the Asgardarchaeota, making it the first reported non-methanogenic archaeal lineage with an inferred complete Pyl machinery, likely providing members of this class with an efficient mechanism for methylamine utilisation. Furthermore, we identified enzymes for the biosynthesis of ester-type lipids, characteristic of bacteria and eukaryotes, in both newly described classes, supporting the hypothesis that mixed ether-ester lipids are a shared feature among Asgardarchaeota.

Phylogenetic Diversity of Lhr Proteins and Biochemical Activities of the Thermococcales aLhr2 DNA/RNA Helicase

Helicase proteins are known to use the energy of ATP to unwind nucleic acids and to remodel protein-nucleic acid complexes. They are involved in almost every aspect of DNA and RNA metabolisms and participate in numerous repair mechanisms that maintain cellular integrity. The archaeal Lhr-type proteins are SF2 helicases that are mostly uncharacterized. They have been proposed to be DNA helicases that act in DNA recombination and repair processes in Sulfolobales and Methanothermobacter. In Thermococcales, a protein annotated as an Lhr2 protein was found in the network of proteins involved in RNA metabolism. To investigate this, we performed in-depth phylogenomic analyses to report the classification and taxonomic distribution of Lhr-type proteins in Archaea, and to better understand their relationship with bacterial Lhr. Furthermore, with the goal of envisioning the role(s) of aLhr2 in Thermococcales cells, we deciphered the enzymatic activities of aLhr2 from Thermococcus barophilus (Tbar). We showed that Tbar-aLhr2 is a DNA/RNA helicase with a significant annealing activity that is involved in processes dependent on DNA and RNA transactions.

Phylogenomic Insights into the Origin of Primary Plastids

The origin of plastids was a major evolutionary event that paved the way for an astonishing diversification of photosynthetic eukaryotes. Plastids originated by endosymbiosis between a heterotrophic eukaryotic host and cyanobacteria, presumably in a common ancestor of the primary photosynthetic eukaryotes (Archaeplastida). A single origin of primary plastids is well supported by plastid evidence but not by nuclear phylogenomic analyses, which have consistently failed to recover the monophyly of Archaeplastida hosts. Importantly, plastid monophyly and non-monophyletic hosts could be explained under scenarios of independent or serial eukaryote-to-eukaryote endosymbioses. Here, we assessed the strength of the signal for the monophyly of Archaeplastida hosts in four available phylogenomic datasets. The effect of phylogenetic methodology, data quality, alignment trimming strategy, gene and taxon sampling, and the presence of outlier genes were investigated. Our analyses revealed a lack of support for host monophyly in the shorter individual datasets. However, when analyzed together under rigorous data curation and complex mixture models, the combined nuclear datasets supported the monophyly of primary photosynthetic eukaryotes (Archaeplastida) and revealed a putative association with plastid-lacking Picozoa. This study represents an important step towards better understanding deep eukaryotic evolution and the origin of plastids.

Gregarine single-cell transcriptomics reveals differential mitochondrial remodeling and adaptation in apicomplexans

BACKGROUND

Apicomplexa is a diverse phylum comprising unicellular endobiotic animal parasites and contains some of the most well-studied microbial eukaryotes including the devastating human pathogens Plasmodium falciparum and Cryptosporidium hominis. In contrast, data on the invertebrate-infecting gregarines remains sparse and their evolutionary relationship to other apicomplexans remains obscure. Most apicomplexans retain a highly modified plastid, while their mitochondria remain metabolically conserved. Cryptosporidium spp. inhabit an anaerobic host-gut environment and represent the known exception, having completely lost their plastid while retaining an extremely reduced mitochondrion that has lost its genome. Recent advances in single-cell sequencing have enabled the first broad genome-scale explorations of gregarines, providing evidence of differential plastid retention throughout the group. However, little is known about the retention and metabolic capacity of gregarine mitochondria.

RESULTS

Here, we sequenced transcriptomes from five species of gregarines isolated from cockroaches. We combined these data with those from other apicomplexans, performed detailed phylogenomic analyses, and characterized their mitochondrial metabolism. Our results support the placement of Cryptosporidium as the earliest diverging lineage of apicomplexans, which impacts our interpretation of evolutionary events within the phylum. By mapping in silico predictions of core mitochondrial pathways onto our phylogeny, we identified convergently reduced mitochondria. These data show that the electron transport chain has been independently lost three times across the phylum, twice within gregarines.

CONCLUSIONS

Apicomplexan lineages show variable functional restructuring of mitochondrial metabolism that appears to have been driven by adaptations to parasitism and anaerobiosis. Our findings indicate that apicomplexans are rife with convergent adaptations, with shared features including morphology, energy metabolism, and intracellularity.

Vestiges of the Bacterial Signal Recognition Particle-Based Protein Targeting in Mitochondria

The main bacterial pathway for inserting proteins into the plasma membrane relies on the signal recognition particle (SRP), composed of the Ffh protein and an associated RNA component, and the SRP-docking protein FtsY. Eukaryotes use an equivalent system of archaeal origin to deliver proteins into the endoplasmic reticulum, whereas a bacteria-derived SRP and FtsY function in the plastid. Here we report on the presence of homologs of the bacterial Ffh and FtsY proteins in various unrelated plastid-lacking unicellular eukaryotes, namely Heterolobosea, Alveida, Goniomonas, and Hemimastigophora. The monophyly of novel eukaryotic Ffh and FtsY groups, predicted mitochondrial localization experimentally confirmed for Naegleria gruberi, and a strong alphaproteobacterial affinity of the Ffh group, collectively suggest that they constitute parts of an ancestral mitochondrial signal peptide-based protein-targeting system inherited from the last eukaryotic common ancestor, but lost from the majority of extant eukaryotes. The ability of putative signal peptides, predicted in a subset of mitochondrial-encoded N. gruberi proteins, to target a reporter fluorescent protein into the endoplasmic reticulum of Trypanosoma brucei, likely through their interaction with the cytosolic SRP, provided further support for this notion. We also illustrate that known mitochondrial ribosome-interacting proteins implicated in membrane protein targeting in opisthokonts (Mba1, Mdm38, and Mrx15) are broadly conserved in eukaryotes and nonredundant with the mitochondrial SRP system. Finally, we identified a novel mitochondrial protein (MAP67) present in diverse eukaryotes and related to the signal peptide-binding domain of Ffh, which may well be a hitherto unrecognized component of the mitochondrial membrane protein-targeting machinery.

A molecular timescale for eukaryote evolution with implications for the origin of red algal-derived plastids

In modern oceans, eukaryotic phytoplankton is dominated by lineages with red algal-derived plastids such as diatoms, dinoflagellates, and coccolithophores. Despite the ecological importance of these groups and many others representing a huge diversity of forms and lifestyles, we still lack a comprehensive understanding of their evolution and how they obtained their plastids. New hypotheses have emerged to explain the acquisition of red algal-derived plastids by serial endosymbiosis, but the chronology of these putative independent plastid acquisitions remains untested. Here, we establish a timeframe for the origin of red algal-derived plastids under scenarios of serial endosymbiosis, using Bayesian molecular clock analyses applied on a phylogenomic dataset with broad sampling of eukaryote diversity. We find that the hypotheses of serial endosymbiosis are chronologically possible, as the stem lineages of all red plastid-containing groups overlap in time. This period in the Meso- and Neoproterozoic Eras set the stage for the later expansion to dominance of red algal-derived primary production in the contemporary oceans, which profoundly altered the global geochemical and ecological conditions of the Earth.

Ancestral sequence reconstruction - An underused approach to understand the evolution of gene function in plants?

Whilst substantial research effort has been placed on understanding the interactions of plant proteins with their molecular partners, relatively few studies in plants - by contrast to work in other organisms - address how these interactions evolve. It is thought that ancestral proteins were more promiscuous than modern proteins and that specificity often evolved following gene duplication and subsequent functional refining. However, ancestral protein resurrection studies have found that some modern proteins have evolved de novo from ancestors lacking those functions. Intriguingly, the new interactions evolved as a consequence of just a few mutations and, as such, acquisition of new functions appears to be neither difficult nor rare, however, only a few of them are incorporated into biological processes before they are lost to subsequent mutations. Here, we detail the approach of ancestral sequence reconstruction (ASR), providing a primer to reconstruct the sequence of an ancestral gene. We will present case studies from a range of different eukaryotes before discussing the few instances where ancestral reconstructions have been used in plants. As ASR is used to dig into the remote evolutionary past, we will also present some alternative genetic approaches to investigate molecular evolution on shorter timescales. We argue that the study of plant secondary metabolism is particularly well suited for ancestral reconstruction studies. Indeed, its ancient evolutionary roots and highly diverse landscape provide an ideal context in which to address the focal issue around the emergence of evolutionary novelties and how this affects the chemical diversification of plant metabolism.

Markers for genetic change

Background and aims

Wildlife conservation has focused primarily on species for the last decades. Recently, popular perception and laws have begun to recognize the central importance of genetic diversity in the conservation of biodiversity. How to incorporate genetic diversity in ongoing monitoring and management of wildlife is still an open question.

Methods

We tested a panel of multiplexed, high-throughput sequenced introns in the small mammal communities of two UNESCO World Heritage Sites on different continents to assess their viability for large-scale monitoring of genetic variability in a spectrum of diverse species. To enhance applicability across other systems, the bioinformatic pipeline for primer design was outlined.

Results

The number of loci amplified and amplification evenness decreased as phylogenetic distance increased from the reference taxa, yet several loci were still variable across multiple mammal orders.

Conclusions

Genetic variability found is informative for population genetic analyses and for addressing phylogeographic and phylogenetic questions, illustrated by small mammal examples here.

Automated Removal of Non-homologous Sequence Stretches with PREQUAL

Large-scale multigene datasets used in phylogenomics and comparative genomics often contain sequence errors inherited from source genomes and transcriptomes. These errors typically manifest as stretches of non-homologous characters and derive from sequencing, assembly, and/or annotation errors. The lack of automatic tools to detect and remove sequence errors leads to the propagation of these errors in large-scale datasets. PREQUAL is a command line tool that identifies and masks regions with non-homologous adjacent characters in sets of unaligned homologous sequences. PREQUAL uses a full probabilistic approach based on pair hidden Markov models. On the front end, PREQUAL is user-friendly and simple to use while also allowing full customization to adjust filtering sensitivity. It is primarily aimed at amino acid sequences but can handle protein-coding nucleotide sequences. PREQUAL is computationally efficient and shows high sensitivity and accuracy. In this chapter, we briefly introduce the motivation for PREQUAL and its underlying methodology, followed by a description of basic and advanced usage, and conclude with some notes and recommendations. PREQUAL fills an important gap in the current bioinformatics tool kit for phylogenomics, contributing toward increased accuracy and reproducibility in future studies.

Phylogenomics and the Genetic Architecture of the Placental Mammal Radiation

The genomes of placental mammals are being sequenced at an unprecedented rate. Alignments of hundreds, and one day thousands, of genomes spanning the rich living and extinct diversity of species offer unparalleled power to resolve phylogenetic controversies, identify genomic innovations of adaptation, and dissect the genetic architecture of reproductive isolation. We highlight outstanding questions about the earliest phases of placental mammal diversification and the promise of newer methods, as well as remaining challenges, toward using whole genome data to resolve placental mammal phylogeny. The next phase of mammalian comparative genomics will see the completion and application of finished-quality, gapless genome assemblies from many ordinal lineages and closely related species. Interspecific comparisons between the most hypervariable genomic loci will likely reveal large, but heretofore mostly underappreciated, effects on population divergence, morphological innovation, and the origin of new species.