The evolutionary diversification of LSF and Grainyhead transcription factors preceded the radiation of basal animal lineages

<p>Abstract</p> <p>Background</p> <p>The transcription factors of the LSF/Grainyhead (GRH) family are characterized by the possession of a distinctive DNA-binding domain that bears no clear relationship to other known DNA-binding domains, with the possible exception of the p53 core domain. In triploblastic animals, the LSF and GRH subfamilies have diverged extensively with respect to their biological roles, general expression patterns, and mechanism of DNA binding. For example, <it>Grainyhead </it>(GRH) homologs are expressed primarily in the epidermis, and they appear to play an ancient role in maintaining the epidermal barrier. By contrast, LSF homologs are more widely expressed, and they regulate general cellular functions such as cell cycle progression and survival in addition to cell-lineage specific gene expression.</p> <p>Results</p> <p>To illuminate the early evolution of this family and reconstruct the functional divergence of LSF and GRH, we compared homologs from 18 phylogenetically diverse taxa, including four basal animals (<it>Nematostella vectensis</it>, <it>Vallicula multiformis</it>, <it>Trichoplax adhaerens</it>, and <it>Amphimedon queenslandica</it>), a choanoflagellate (<it>Monosiga brevicollis</it>) and several fungi. Phylogenetic and bioinformatic analyses of these sequences indicate that (1) the LSF/GRH gene family originated prior to the animal-fungal divergence, and (2) the functional diversification of the LSF and GRH subfamilies occurred prior to the divergence between sponges and eumetazoans. Aspects of the domain architecture of LSF/GRH proteins are well conserved between fungi, choanoflagellates, and metazoans, though within the Metazoa, the LSF and GRH families are clearly distinct. We failed to identify a convincing LSF/GRH homolog in the sequenced genomes of the algae <it>Volvox carteri </it>and <it>Chlamydomonas reinhardtii </it>or the amoebozoan <it>Dictyostelium purpureum</it>. Interestingly, the ancestral GRH locus has become split into two separate loci in the sea anemone <it>Nematostella</it>, with one locus encoding a DNA binding domain and the other locus encoding the dimerization domain.</p> <p>Conclusions</p> <p>In metazoans, LSF and GRH proteins play a number of roles that are essential to achieving and maintaining multicellularity. It is now clear that this protein family already existed in the unicellular ancestor of animals, choanoflagellates, and fungi. However, the diversification of distinct LSF and GRH subfamilies appears to be a metazoan invention. Given the conserved role of GRH in maintaining epithelial integrity in vertebrates, insects, and nematodes, it is noteworthy that the evolutionary origin of Grh appears roughly coincident with the evolutionary origin of the epithelium.</p

Deep Genomic-Scale Analyses of the Metazoa Reject Coelomata: Evidence from Single- and Multigene Families Analyzed Under a Supertree and Supermatrix Paradigm

Solving the phylogeny of the animals with bilateral symmetry has proven difficult. Morphological studies have suggested a variety of alternative hypotheses, of which, Hyman’s Coelomata hypothesis has become the most established. Studies based on 18S rRNA have failed to endorse Coelomata, supporting instead the rearrangement of the protostomes into two new clades: the Lophotrochozoa (including, e.g., the molluscs and the annelids) and the Ecdysozoa (including the Panarthropoda and most pseudocoelomates, such as the nematodes and priapulids). Support for this new animal phylogeny has been attained from expressed sequence tag studies, although these generally have a limited gene sampling. In contrast, deep genomic-scale analyses have often supported Coelomata. However, these studies are problematic due to their limited taxonomic sampling, which could exacerbate tree reconstruction artifacts

Widespread Recurrent Evolution of Genomic Features

The recent explosion of genome sequences from all major phylogenetic groups has unveiled an unexpected wealth of cases of recurrent evolution of strikingly similar genomic features in different lineages. Here, we review the diverse known types of recurrent evolution in eukaryotic genomes, with a special focus on metazoans, ranging from reductive genome evolution to origins of splice-leader trans-splicing, from tandem exon duplications to gene family expansions. We first propose a general classification scheme for evolutionary recurrence at the genomic level, based on the type of driving force—mutation or selection—and the environmental and genomic circumstances underlying these forces. We then discuss various cases of recurrent genomic evolution under this scheme. Finally, we provide a broader context for repeated genomic evolution, including the unique relationship of genomic recurrence with the genotype–phenotype map, and the ways in which the study of recurrent genomic evolution can be used to understand fundamental evolutionary processes

Relative Timing of Intron Gain and a New Marker for Phylogenetic Analyses

Despite decades of effort by molecular systematists, the trees of life of eukaryotic organisms still remain partly unresolved or in conflict with each other. An ever increasing number of fully-sequenced genomes of various eukaryotes allows to consider gene and species phylogenies at genome-scale. However, such phylogenomics-based approaches also revealed that more taxa and more and more gene sequences are not the ultimate solution to fully resolve these conflicts, and that there is a need for sequence-independent phylogenetic meta-characters that are derived from genome sequences. Spliceosomal introns are characteristic features of eukaryotic nuclear genomes. The relatively rare changes of spliceosomal intron positions have already been used as genome-level markers, both for the estimation of intron evolution and phylogenies, however with variable success. In this thesis, a specific subset of these changes is introduced and established as a novel phylogenetic marker, termed near intron pair (NIP). These characters are inferred from homologous genes that contain mutually-exclusive intron presences at pairs of coding sequence (CDS) positions in close proximity. The idea that NIPs are powerful characters is based on the assumption that both very small exons and multiple intron gains at the same position are rare. To obtain sufficient numbers of NIP character data from genomic and alignment data sets in a consistent and flexible way, the implementation of a computational pipeline was a main goal of this work. Starting from orthologous (or more general: homologous) gene datasets comprising genomic sequences and corresponding CDS transcript annotations, the multiple alignment generation is an integral part of this pipeline. The alignment can be calculated at the amino acid level utilizing external tools (e.g. transAlign) and results in a codon alignment via back-translation. Guided by the multiple alignment, the positionally homologous intron positions should become apparent when mapped individually for each transcript. The pipeline proceeds at this stage to output portions of the intron-annotated alignment that contain at least one candidate of a NIP character. In a subsequent pipeline script, these collected so-called NIP region files are finally converted to binary state characters representing valid NIPs in dependence of quality filter constraints concerning, e.g., the amino acid alignment conservation around intron loci and splice sites, to name a few. The computational pipeline tools provide the researcher to elaborate on NIP character matrices that can be used for tree inference, e.g., using the maximum parsimony approach. In a first NIP-based application, the phylogenetic position of major orders of holometabolic insects (more specifically: the Coleoptera-Hymenoptera-Mecopterida trifurcation) was evaluated in a cladistic sense. As already suggested during a study on the eIF2gamma gene based on two NIP cases (Krauss et al. 2005), the genome-scale evaluation supported Hymenoptera as sister group to an assemblage of Coleoptera and Mecopterida, in agreement with other studies, but contradicting the previously established view. As part of the genome paper describing a new species of twisted-wing parasites (Strepsiptera), the NIP method was employed to help to resolve the phylogenetic position of them within (holometabolic) insects. Together with analyses of sequence patterns and a further meta-character, it revealed twisted-wing parasites as being the closest relatives of the mega-diverse beetles. NIP-based reconstructions of the metazoan tree covering a broad selection of representative animal species also identified some weaknesses of the NIP approach that may suffer e.g. from alignment/ortholog prediction artifacts (depending on the depth of range of taxa) and systematic biases (long branch attraction artifacts, due to unequal evolutionary rates of intron gain/loss and the use of the maximum parsimony method). In a further study, the identification of NIPs within the recently diverged genus Drosophila could be utilized to characterize recent intron gain events that apparently involved several cases of intron sliding and tandem exon duplication, albeit the mechanisms of gain for the majority of cases could not be elucidated. Finally, the NIP marker could be established as a novel phylogenetic marker, in particular dedicated to complementarily explore the wealth of genome data for phylogenetic purposes and to address open questions of intron evolution

Powdery mildew fungal effector candidates share N-terminal Y/F/WxC-motif

Extent: 13p.Background: Powdery mildew and rust fungi are widespread, serious pathogens that depend on developing haustoria in the living plant cells. Haustoria are separated from the host cytoplasm by a plant cell-derived extrahaustorial membrane. They secrete effector proteins, some of which are subsequently transferred across this membrane to the plant cell to suppress defense. Results: In a cDNA library from barley epidermis containing powdery mildew haustoria, two-thirds of the sequenced ESTs were fungal and represented ~3,000 genes. Many of the most highly expressed genes encoded small proteins with N-terminal signal peptides. While these proteins are novel and poorly related, they do share a three-amino acid motif, which we named "Y/F/WxC", in the N-terminal of the mature proteins. The first amino acid of this motif is aromatic: tyrosine, phenylalanine or tryptophan, and the last is always cysteine. In total, we identified 107 such proteins, for which the ESTs represent 19% of the fungal clones in our library, suggesting fundamental roles in haustoria function. While overall sequence similarity between the powdery mildew Y/F/WxC-proteins is low, they do have a highly similar exon-intron structure, suggesting they have a common origin. Interestingly, searches of public fungal genome and EST databases revealed that haustoria-producing rust fungi also encode large numbers of novel, short proteins with signal peptides and the Y/F/WxC-motif. No significant numbers of such proteins were identified from genome and EST sequences from either fungi which do not produce haustoria or from haustoria-producing Oomycetes. Conclusion: In total, we identified 107, 178 and 57 such Y/F/WxC-proteins from the barley powdery mildew, the wheat stem rust and the wheat leaf rust fungi, respectively. All together, our findings suggest the Y/F/WxC-proteins to be a new class of effectors from haustoria-producing pathogenic fungi.Dale Godfrey, Henrik Böhlenius, Carsten Pedersen, Ziguo Zhang, Jeppe Emmersen and Hans Thordal-Christense

A tale of two clades: genome evolution of oomycetes and fungi.

Some of the most ecologically-significant pathogens of plants, animals and marine life come from two groups of filamentous eukaryotes; the oomycetes and the fungi. Although similar in morphology and ecological niche, the two groups are only very-distantly related in terms of evolutionary history. The oomycetes are underresearched in evolutionary science, despite their historical and contemporary impact on food and environmental security. In contrast, fungi themselves are probably the most densely studied and sequenced group of organisms in evolutionary science outside of bacteria. This thesis is a collection of five published computational studies of the evolutionary biology of oomycetes and fungi. The first study is a systematic investigation of bacterial horizontal gene transfer into plant pathogenic oomycete species, which identifies 5 potential HGT events from prokaryotes into multiple oomycetes. The second study is a reconstruction of the evolutionary history of the oomycetes using wholegenome data from 37 species, which supports the larger groups within the oomycetes class but suggests that some exemplar oomycete genera are paraphyletic. Taking advantage of the abundance of genomics data available for all major fungal phyla, the third study reconstructs the evolutionary history of 84 fungal species using seven different phylogenomic techniques and critically evaluates each technique for accuracy, speed and other criteria. The fourth study looks at the pangenomes of four model fungal species, and compares the evolution of genomic variation, virulence and environmental adaptation within each species. The final study presents a refined iteration of the methodology used in the previous pangenome study as a self-contained software package and demonstrates the software’s capabilities through pangenome analysis and re-analysis of both model and non-model fungal species. Together, these studies cover a breadth of molecular evolution, comparative genomics, phylogenomics and pangenomics research for two similar, but evolutionarily-distinct groups of important microscopic eukaryotes