DELLA functions evolved by rewiring of associated transcriptional networks.

DELLA proteins are land-plant specific transcriptional regulators that transduce environmental information to multiple processes throughout a plant's life1-3. The molecular basis for this critical function in angiosperms has been linked to the regulation of DELLA stability by gibberellins and to the capacity of DELLA proteins to interact with hundreds of transcription factors4,5. Although bryophyte orthologues can partially fulfil functions attributed to angiosperm DELLA6,7, it is not clear whether the capacity to establish interaction networks is an ancestral property of DELLA proteins or is associated with their role in gibberellin signalling8-10. Here we show that representative DELLAs from the main plant lineages display a conserved ability to interact with multiple transcription factors. We propose that promiscuity was encoded in the ancestral DELLA protein, and that this property has been largely maintained, whereas the lineage-dependent diversification of DELLA-dependent functions mostly reflects the functional evolution of their interacting partners.

Transposable element variants and their potential adaptive impact in urban populations of the malaria vector Anopheles coluzzii.

Anopheles coluzzii is one of the primary vectors of human malaria in sub-Saharan Africa. Recently, it has spread into the main cities of Central Africa threatening vector control programs. The adaptation of An. coluzzii to urban environments partly results from an increased tolerance to organic pollution and insecticides. Some of the molecular mechanisms for ecological adaptation are known, but the role of transposable elements (TEs) in the adaptive processes of this species has not been studied yet. As a first step toward assessing the role of TEs in rapid urban adaptation, we sequenced using long reads six An. coluzzii genomes from natural breeding sites in two major Central Africa cities. We de novo annotated TEs in these genomes and in an additional high-quality An. coluzzii genome, and we identified 64 new TE families. TEs were nonrandomly distributed throughout the genome with significant differences in the number of insertions of several superfamilies across the studied genomes. We identified seven putatively active families with insertions near genes with functions related to vectorial capacity, and several TEs that may provide promoter and transcription factor binding sites to insecticide resistance and immune-related genes. Overall, the analysis of multiple high-quality genomes allowed us to generate the most comprehensive TE annotation in this species to date and identify several TE insertions that could potentially impact both genome architecture and the regulation of functionally relevant genes. These results provide a basis for future studies of the impact of TEs on the biology of An. coluzzii.

The transposable element-rich genome of the cereal pest Sitophilus oryzae.

BACKGROUND: The rice weevil Sitophilus oryzae is one of the most important agricultural pests, causing extensive damage to cereal in fields and to stored grains. S. oryzae has an intracellular symbiotic relationship (endosymbiosis) with the Gram-negative bacterium Sodalis pierantonius and is a valuable model to decipher host-symbiont molecular interactions. RESULTS: We sequenced the Sitophilus oryzae genome using a combination of short and long reads to produce the best assembly for a Curculionidae species to date. We show that S. oryzae has undergone successive bursts of transposable element (TE) amplification, representing 72% of the genome. In addition, we show that many TE families are transcriptionally active, and changes in their expression are associated with insect endosymbiotic state. S. oryzae has undergone a high gene expansion rate, when compared to other beetles. Reconstruction of host-symbiont metabolic networks revealed that, despite its recent association with cereal weevils (30 kyear), S. pierantonius relies on the host for several amino acids and nucleotides to survive and to produce vitamins and essential amino acids required for insect development and cuticle biosynthesis. CONCLUSIONS: Here we present the genome of an agricultural pest beetle, which may act as a foundation for pest control. In addition, S. oryzae may be a useful model for endosymbiosis, and studying TE evolution and regulation, along with the impact of TEs on eukaryotic genomes.

Coordination between growth and stress responses by DELLA in the liverwort Marchantia polymorpha.

Plant survival depends on the optimal use of resources under variable environmental conditions. Among the mechanisms that mediate the balance between growth, differentiation, and stress responses, the regulation of transcriptional activity by DELLA proteins stands out. In angiosperms, DELLA accumulation promotes defense against biotic and abiotic stress and represses cell division and expansion, while the loss of DELLA function is associated with increased plant size and sensitivity toward stress.1 Given that DELLA protein stability is dependent on gibberellin (GA) levels2 and GA metabolism is influenced by the environment,3 this pathway is proposed to relay environmental information to the transcriptional programs that regulate growth and stress responses in angiosperms.4,5 However, DELLA genes are also found in bryophytes, whereas canonical GA receptors have been identified only in vascular plants.6-10 Thus, it is not clear whether these regulatory functions of DELLA predated or emerged with typical GA signaling. Here, we show that, as in vascular plants, the only DELLA in the liverwort Marchantia polymorpha also participates in the regulation of growth and key developmental processes and promotes oxidative stress tolerance. Moreover, part of these effects is likely caused by the conserved physical interaction with the MpPIF transcription factor. Therefore, we suggest that the role in the coordination of growth and stress responses was already encoded in the DELLA protein of the common ancestor of land plants, and the importance of this function is underscored by its conservation over the past 450 million years.

Genomic adaptations to aquatic and aerial life in mayflies and the origin of insect wings.

The evolution of winged insects revolutionized terrestrial ecosystems and led to the largest animal radiation on Earth. However, we still have an incomplete picture of the genomic changes that underlay this diversification. Mayflies, as one of the sister groups of all other winged insects, are key to understanding this radiation. Here, we describe the genome of the mayfly Cloeon dipterum and its gene expression throughout its aquatic and aerial life cycle and specific organs. We discover an expansion of odorant-binding-protein genes, some expressed specifically in breathing gills of aquatic nymphs, suggesting a novel sensory role for this organ. In contrast, flying adults use an enlarged opsin set in a sexually dimorphic manner, with some expressed only in males. Finally, we identify a set of wing-associated genes deeply conserved in the pterygote insects and find transcriptomic similarities between gills and wings, suggesting a common genetic program. Globally, this comprehensive genomic and transcriptomic study uncovers the genetic basis of key evolutionary adaptations in mayflies and winged insects.

An update on the Symbiotic Genomes Database (SymGenDB): a collection of metadata, genomic, genetic and protein sequences, orthologs and metabolic networks of symbiotic organisms.

The Symbiotic Genomes Database (SymGenDB; http://symbiogenomesdb.uv.es/) is a public resource of manually curated associations between organisms involved in symbiotic relationships, maintaining a catalog of completely sequenced/finished bacterial genomes exclusively. It originally consisted of three modules where users could search for the bacteria involved in a specific symbiotic relationship, their genomes and their genes (including their orthologs). In this update, we present an additional module that includes a representation of the metabolic network of each organism included in the database, as Directed Acyclic Graphs (MetaDAGs). This module provides unique opportunities to explore the metabolism of each individual organism and/or to evaluate the shared and joint metabolic capabilities of the organisms of the same genera included in our listing, allowing users to construct predictive analyses of metabolic associations and complementation between systems. We also report a ~25% increase in manually curated content in the database, i.e. bacterial genomes and their associations, with a final count of 2328 bacterial genomes associated to 498 hosts. We describe new querying possibilities for all the modules, as well as new display features for the MetaDAGs module, providing a relevant range of content and utility. This update continues to improve SymGenDB and can help elucidate the mechanisms by which organisms depend on each other.

Transposable elements contribute to the genomic response to insecticides in Drosophila melanogaster.

Most of the genotype-phenotype analyses to date have largely centred attention on single nucleotide polymorphisms. However, transposable element (TE) insertions have arisen as a plausible addition to the study of the genotypic-phenotypic link because of to their role in genome function and evolution. In this work, we investigate the contribution of TE insertions to the regulation of gene expression in response to insecticides. We exposed four Drosophila melanogaster strains to malathion, a commonly used organophosphate insecticide. By combining information from different approaches, including RNA-seq and ATAC-seq, we found that TEs can contribute to the regulation of gene expression under insecticide exposure by rewiring cis-regulatory networks. This article is part of a discussion meeting issue 'Crossroads between transposons and gene regulation'.

Phylogenomics Identifies an Ancestral Burst of Gene Duplications Predating the Diversification of Aphidomorpha.

Aphids (Aphidoidea) are a diverse group of hemipteran insects that feed on plant phloem sap. A common finding in studies of aphid genomes is the presence of a large number of duplicated genes. However, when these duplications occurred remains unclear, partly due to the high relatedness of sequenced species. To better understand the origin of aphid duplications we sequenced and assembled the genome of Cinara cedri, an early branching lineage (Lachninae) of the Aphididae family. We performed a phylogenomic comparison of this genome with 20 other sequenced genomes, including the available genomes of five other aphids, along with the transcriptomes of two species belonging to Adelgidae (a closely related clade to the aphids) and Coccoidea. We found that gene duplication has been pervasive throughout the evolution of aphids, including many parallel waves of recent, species-specific duplications. Most notably, we identified a consistent set of very ancestral duplications, originating from a large-scale gene duplication predating the diversification of Aphidomorpha (comprising aphids, phylloxerids, and adelgids). Genes duplicated in this ancestral wave are enriched in functions related to traits shared by Aphidomorpha, such as association with endosymbionts, and adaptation to plant defenses and phloem-sap-based diet. The ancestral nature of this duplication wave (106-227 Ma) and the lack of sufficiently conserved synteny make it difficult to conclude whether it originated from a whole-genome duplication event or, alternatively, from a burst of large-scale segmental duplications. Genome sequencing of other aphid species belonging to different Aphidomorpha and related lineages may clarify these findings.

Tremblaya phenacola PPER: an evolutionary beta-gammaproteobacterium collage.

Many insects rely on bacterial endosymbionts to obtain nutrients that are scarce in their highly specialized diets. The most surprising example corresponds to the endosymbiotic system found in mealybugs from subfamily Pseudococcinae in which two bacteria, the betaproteobacterium 'Candidatus Tremblaya princeps' and a gammaproteobacterium, maintain a nested endosymbiotic consortium. In the sister subfamily Phenacoccinae, however, a single beta-endosymbiont, 'Candidatus Tremblaya phenacola', has been described. In a previous study, we detected a trpB gene of gammaproteobacterial origin in 'Ca. Tremblaya phenacola' from two Phenacoccus species, apparently indicating an unusual case of horizontal gene transfer (HGT) in a bacterial endosymbiont. What we found by sequencing the genome of 'Ca. Tremblaya phenacola' PPER, single endosymbiont of Phenacoccus peruvianus, goes beyond a HGT phenomenon. It rather represents a genome fusion between a beta and a gammaproteobacterium, followed by massive rearrangements and loss of redundant genes, leading to an unprecedented evolutionary collage. Mediated by the presence of several repeated sequences, there are many possible genome arrangements, and different subgenomic sequences might coexist within the same population.

Evolutionary Analysis of DELLA-Associated Transcriptional Networks.

DELLA proteins are transcriptional regulators present in all land plants which have been shown to modulate the activity of over 100 transcription factors in Arabidopsis, involved in multiple physiological and developmental processes. It has been proposed that DELLAs transduce environmental information to pre-wired transcriptional circuits because their stability is regulated by gibberellins (GAs), whose homeostasis largely depends on environmental signals. The ability of GAs to promote DELLA degradation coincides with the origin of vascular plants, but the presence of DELLAs in other land plants poses at least two questions: what regulatory properties have DELLAs provided to the behavior of transcriptional networks in land plants, and how has the recruitment of DELLAs by GA signaling affected this regulation. To address these issues, we have constructed gene co-expression networks of four different organisms within the green lineage with different properties regarding DELLAs: Arabidopsis thaliana and Solanum lycopersicum (both with GA-regulated DELLA proteins), Physcomitrella patens (with GA-independent DELLA proteins) and Chlamydomonas reinhardtii (a green alga without DELLA), and we have examined the relative evolution of the subnetworks containing the potential DELLA-dependent transcriptomes. Network analysis indicates a relative increase in parameters associated with the degree of interconnectivity in the DELLA-associated subnetworks of land plants, with a stronger effect in species with GA-regulated DELLA proteins. These results suggest that DELLAs may have played a role in the coordination of multiple transcriptional programs along evolution, and the function of DELLAs as regulatory 'hubs' became further consolidated after their recruitment by GA signaling in higher plants.

The genomic sequence of Exiguobacterium chiriqhucha str. N139 reveals a species that thrives in cold waters and extreme environmental conditions.

We report the genome sequence of Exiguobacterium chiriqhucha str. N139, isolated from a high-altitude Andean lake. Comparative genomic analyses of the Exiguobacterium genomes available suggest that our strain belongs to the same species as the previously reported E. pavilionensis str. RW-2 and Exiguobacterium str. GIC 31. We describe this species and propose the chiriqhucha name to group them. 'Chiri qhucha' in Quechua means 'cold lake', which is a common origin of these three cosmopolitan Exiguobacteria. The 2,952,588-bp E. chiriqhucha str. N139 genome contains one chromosome and three megaplasmids. The genome analysis of the Andean strain suggests the presence of enzymes that confer E. chiriqhucha str. N139 the ability to grow under multiple environmental extreme conditions, including high concentrations of different metals, high ultraviolet B radiation, scavenging for phosphorous and coping with high salinity. Moreover, the regulation of its tryptophan biosynthesis suggests that novel pathways remain to be discovered, and that these pathways might be fundamental in the amino acid metabolism of the microbial community from Laguna Negra, Argentina.

SymbioGenomesDB: a database for the integration and access to knowledge on host-symbiont relationships.

Symbiotic relationships occur naturally throughout the tree of life, either in a commensal, mutualistic or pathogenic manner. The genomes of multiple organisms involved in symbiosis are rapidly being sequenced and becoming available, especially those from the microbial world. Currently, there are numerous databases that offer information on specific organisms or models, but none offer a global understanding on relationships between organisms, their interactions and capabilities within their niche, as well as their role as part of a system, in this case, their role in symbiosis. We have developed the SymbioGenomesDB as a community database resource for laboratories which intend to investigate and use information on the genetics and the genomics of organisms involved in these relationships. The ultimate goal of SymbioGenomesDB is to host and support the growing and vast symbiotic-host relationship information, to uncover the genetic basis of such associations. SymbioGenomesDB maintains a comprehensive organization of information on genomes of symbionts from diverse hosts throughout the Tree of Life, including their sequences, their metadata and their genomic features. This catalog of relationships was generated using computational tools, custom R scripts and manual integration of data available in public literature. As a highly curated and comprehensive systems database, SymbioGenomesDB provides web access to all the information of symbiotic organisms, their features and links to the central database NCBI. Three different tools can be found within the database to explore symbiosis-related organisms, their genes and their genomes. Also, we offer an orthology search for one or multiple genes in one or multiple organisms within symbiotic relationships, and every table, graph and output file is downloadable and easy to parse for further analysis. The robust SymbioGenomesDB will be constantly updated to cope with all the data being generated and included in major databases, in order to serve as an important, useful and timesaving tool. Database URL: http://symbiogenomesdb.uv.es.

Reconstructing and mining the B cell repertoire with ImmunediveRsity.

The B cell antigen receptor repertoire is highly diverse and constantly modified by clonal selection. High-throughput DNA sequencing (HTS) of the lymphocyte repertoire (Rep-Seq) represents a promising technology to explore such diversity ex-vivo and assist in the identification of antigen-specific antibodies based on molecular signatures of clonal selection. Therefore, integrative tools for repertoire reconstruction and analysis from antibody sequences are needed. We developed ImmunediveRity, a stand-alone pipeline primarily based in R programming for the integral analysis of B cell repertoire data generated by HTS. The pipeline integrates GNU software and in house scripts to perform quality filtering, sequencing noise correction and repertoire reconstruction based on V, D and J segment assignment, clonal origin and unique heavy chain identification. Post-analysis scripts generate a wealth of repertoire metrics that in conjunction with a rich graphical output facilitates sample comparison and repertoire mining. Its performance was tested with raw and curated human and mouse 454-Roche sequencing benchmarks providing good approximations of repertoire structure. Furthermore, ImmunediveRsity was used to mine the B cell repertoire of immunized mice with a model antigen, allowing the identification of previously validated antigen-specific antibodies, and revealing different and unexpected clonal diversity patterns in the post-immunization IgM and IgG compartments. Although ImmunediveRsity is similar to other recently developed tools, it offers significant advantages that facilitate repertoire analysis and repertoire mining. ImmunediveRsity is open source and free for academic purposes and it runs on 64 bit GNU/Linux and MacOS. Available at: https://bitbucket.org/ImmunediveRsity/immunediversity/.

Genome evolution in the primary endosymbiont of whiteflies sheds light on their divergence.

Whiteflies are important agricultural insect pests, whose evolutionary success is related to a long-term association with a bacterial endosymbiont, Candidatus Portiera aleyrodidarum. To completely characterize this endosymbiont clade, we sequenced the genomes of three new Portiera strains covering the two extant whitefly subfamilies. Using endosymbiont and mitochondrial sequences we estimated the divergence dates in the clade and used these values to understand the molecular evolution of the endosymbiont coding sequences. Portiera genomes were maintained almost completely stable in gene order and gene content during more than 125 Myr of evolution, except in the Bemisia tabaci lineage. The ancestor had already lost the genetic information transfer autonomy but was able to participate in the synthesis of all essential amino acids and carotenoids. The time of divergence of the B. tabaci complex was much more recent than previous estimations. The recent divergence of biotypes B (MEAM1 species) and Q (MED species) suggests that they still could be considered strains of the same species. We have estimated the rates of evolution of Portiera genes, synonymous and nonsynonymous, and have detected significant differences among-lineages, with most Portiera lineages evolving very slowly. Although the nonsynonymous rates were much smaller than the synonymous, the genomic dN/dS ratios were similar, discarding selection as the driver of among-lineage variation. We suggest variation in mutation rate and generation time as the responsible factors. In conclusion, the slow evolutionary rates of Portiera may have contributed to its long-term association with whiteflies, avoiding its replacement by a novel and more efficient endosymbiont.