Identification and phylogenetic analysis of Dictyostelium discoideum kinesin proteins

BACKGROUND: Kinesins constitute a large superfamily of motor proteins in eukaryotic cells. They perform diverse tasks such as vesicle and organelle transport and chromosomal segregation in a microtubule- and ATP-dependent manner. In recent years, the genomes of a number of eukaryotic organisms have been completely sequenced. Subsequent studies revealed and classified the full set of members of the kinesin superfamily expressed by these organisms. For Dictyostelium discoideum, only five kinesin superfamily proteins (Kif's) have already been reported. RESULTS: Here, we report the identification of thirteen kinesin genes exploiting the information from the raw shotgun reads of the Dictyostelium discoideum genome project. A phylogenetic tree of 390 kinesin motor domain sequences was built, grouping the Dictyostelium kinesins into nine subfamilies. According to known cellular functions or strong homologies to kinesins of other organisms, four of the Dictyostelium kinesins are involved in organelle transport, six are implicated in cell division processes, two are predicted to perform multiple functions, and one kinesin may be the founder of a new subclass. CONCLUSION: This analysis of the Dictyostelium genome led to the identification of eight new kinesin motor proteins. According to an exhaustive phylogenetic comparison, Dictyostelium contains the same subset of kinesins that higher eukaryotes need to perform mitosis. Some of the kinesins are implicated in intracellular traffic and a small number have unpredictable functions

Centromere sequence and dynamics in Dictyostelium discoideum

Centromeres play a pivotal role in the life of a eukaryote cell, perform an essential and conserved function, but this has not led to a standard centromere structure. It remains currently unclear, how the centromeric function is achieved by widely differing structures. Since centromeres are often large and consist mainly of repetitive sequences they have only been analyzed in great detail in a handful of organisms. The genome of Dictyostelium discoideum, a valuable model organism, was described a few years ago but its centromere organization remained largely unclear. Using available sequence information we reconstructed the putative centromere organization in three of the six chromosomes of D. discoideum. They mainly consist of one type of transposons that is confined to centromeric regions. Centromeres are dynamic due to transposon integration, but an optimal centromere size seems to exist in D. discoideum. One centromere probably has expanded recently, whereas another underwent major rearrangements

Analyse des Genoms von Dictyostelium discoideum

Dictyostelium discoideum ist eine soziale Amöbe, deren Eigenschaften sie zu einem Model für verschiedene zelluläre Prozesse gemacht haben. Die vorliegende Arbeit beschreibt die Analyse des Genoms dieses meist einzelligen Protisten und wertet die herausragendsten Erkenntnisse aus der Analyse aus. Einige Eigenschaften des Genoms sind ungewöhnlich, wie z.B. der hohe anteil an A und T Nukleotiden oder auch die Organisation der chromosomenenden, der Telomere. Andererseits sind in diesem Organismus Gene vorhanden, die bis jetzt nur mehrzelligen Tiere zugeordnet wurden. Die Genomanalyse dieses Organismus ist die Grundlage für die weitere Beschäftigung mit diesem Organismus als Modell

Gain and loss of polyadenylation signals during evolution of green algae

<p>Abstract</p> <p>Background</p> <p>The Viridiplantae (green algae and land plants) consist of two monophyletic lineages: the Chlorophyta and the Streptophyta. Most green algae belong to the Chlorophyta, while the Streptophyta include all land plants and a small group of freshwater algae known as Charophyceae. Eukaryotes attach a poly-A tail to the 3' ends of most nuclear-encoded mRNAs. In embryophytes, animals and fungi, the signal for polyadenylation contains an A-rich sequence (often AAUAAA or related sequence) 13 to 30 nucleotides upstream from the cleavage site, which is commonly referred to as the near upstream element (NUE). However, it has been reported that the pentanucleotide UGUAA is used as polyadenylation signal for some genes in volvocalean algae.</p> <p>Results</p> <p>We set out to investigate polyadenylation signal differences between streptophytes and chlorophytes that may have emerged shortly after the evolutionary split between Streptophyta and Chlorophyta. We therefore analyzed expressed genes (ESTs) from three streptophyte algae, <it>Mesostigma viride</it>, <it>Klebsormidium subtile </it>and <it>Coleochaete scutata</it>, and from two early-branching chlorophytes, <it>Pyramimonas parkeae </it>and <it>Scherffelia dubia</it>. In addition, to extend the database, our analyses included ESTs from six other chlorophytes (<it>Acetabularia acetabulum</it>, <it>Chlamydomonas reinhardtii</it>, <it>Helicosporidium </it>sp. ex Simulium jonesii, <it>Prototheca wickerhamii, Scenedesmus obliquus </it>and <it>Ulva linza</it>) and one streptophyte (<it>Closterium peracerosum</it>). Our results indicate that polyadenylation signals in green algae vary widely. The UGUAA motif is confined to late-branching Chlorophyta. Most streptophyte algae do not have an A-rich sequence motif like that in embryophytes, animals and fungi. We observed polyadenylation signals similar to those of <it>Arabidopsis </it>and other land plants only in <it>Mesostigma</it>.</p> <p>Conclusion</p> <p>Polyadenylation signals in green algae show considerable variation. A new NUE (UGUAA) was invented in derived chlorophytes and replaced not only the A-rich NUE but the complete poly(A) signal in all chlorophytes investigated except <it>Scherffelia </it>(only NUE replaced) and <it>Pyramimonas </it>(UGUAA completely missing). The UGUAA element is completely absent from streptophytes. However, the structure of the poly(A) signal was often modified in streptophyte algae. In most species investigated, an A-rich NUE is missing; instead, these species seem to rely mainly on U-rich elements.</p

The ancestor of the Paulinella chromatophore obtained a carboxysomal operon by horizontal gene transfer from a Nitrococcus-like γ-proteobacterium

<p>Abstract</p> <p>Background</p> <p><it>Paulinella chromatophora </it>is a freshwater filose amoeba with photosynthetic endosymbionts (chromatophores) of cyanobacterial origin that are closely related to free-living <it>Prochlorococcus </it>and <it>Synechococcus </it>species (PS-clade). Members of the PS-clade of cyanobacteria contain a proteobacterial form 1A RubisCO (ribulose-1,5-bisphosphate carboxylase/oxygenase) that was acquired by horizontal gene transfer (HGT) of a carboxysomal operon. In rDNA-phylogenies, the <it>Paulinella </it>chromatophore diverged basal to the PS-clade, raising the question whether the HGT occurred before or after the split of the chromatophore ancestor.</p> <p>Results</p> <p>Phylogenetic analyses of the almost complete rDNA operon with an improved taxon sampling containing most known cyanobacterial lineages recovered the <it>Paulinella </it>chromatophore as sister to the complete PS-clade. The sequence of the complete carboxysomal operon of <it>Paulinella </it>was determined. Analysis of RubisCO large subunit (<it>rbcL</it>) sequences revealed that <it>Paulinella </it>shares the proteobacterial form 1A RubisCO with the PS-clade. The γ-proteobacterium <it>Nitrococcus mobilis </it>was identified as sister of the <it>Paulinella </it>chromatophore and the PS-clade in the RubisCO phylogeny. Gene content and order in the carboxysomal operon correlates well with the RubisCO phylogeny demonstrating that the complete carboxysomal operon was acquired by the common ancestor of the <it>Paulinella </it>chromatophore and the PS-clade through HGT. The carboxysomal operon shows a significantly elevated AT content in <it>Paulinella</it>, which in the <it>rbcL </it>gene is confined to third codon positions. Combined phylogenies using <it>rbcL </it>and the rDNA-operon resulted in a nearly fully resolved tree of the PS-clade.</p> <p>Conclusion</p> <p>The HGT of the carboxysomal operon predated the divergence of the chromatophore ancestor from the PS-clade. Following HGT and divergence of the chromatophore ancestor, diversification of the PS-clade into at least three subclades occurred. The γ-proteobacterium <it>Nitrococcus mobilis </it>represents the closest known relative to the donor of the carboxysomal operon. The isolated position of the <it>Paulinella </it>chromatophore in molecular phylogenies as well as its elevated AT content suggests that the <it>Paulinella </it>chromatophore has already undergone typical steps in the reductive evolution of an endosymbiont.</p

EST analysis of the scaly green flagellate Mesostigma viride (Streptophyta): Implications for the evolution of green plants (Viridiplantae)

BACKGROUND: The Viridiplantae (land plants and green algae) consist of two monophyletic lineages, the Chlorophyta and the Streptophyta. The Streptophyta include all embryophytes and a small but diverse group of freshwater algae traditionally known as the Charophyceae (e.g. Charales, Coleochaete and the Zygnematales). The only flagellate currently included in the Streptophyta is Mesostigma viride Lauterborn. To gain insight into the genome evolution in streptophytes, we have sequenced 10,395 ESTs from Mesostigma representing 3,300 independent contigs and compared the ESTs of Mesostigma with available plant genomes (Arabidopsis, Oryza, Chlamydomonas), with ESTs from the bryophyte Physcomitrella, the genome of the rhodophyte Cyanidioschyzon, the ESTs from the rhodophyte Porphyra, and the genome of the diatom Thalassiosira. RESULTS: The number of expressed genes shared by Mesostigma with the embryophytes (90.3 % of the expressed genes showing similarity to known proteins) is higher than with Chlamydomonas (76.1 %). In general, cytosolic metabolic pathways, and proteins involved in vesicular transport, transcription, regulation, DNA-structure and replication, cell cycle control, and RNA-metabolism are more conserved between Mesostigma and the embryophytes than between Mesostigma and Chlamydomonas. However, plastidic and mitochondrial metabolic pathways, cytoskeletal proteins and proteins involved in protein folding are more conserved between Mesostigma and Chlamydomonas than between Mesostigma and the embryophytes. CONCLUSION: Our EST-analysis of Mesostigma supports the notion that this organism should be a suitable unicellular model for the last flagellate common ancestor of the streptophytes. Mesostigma shares more genes with the embryophytes than with the chlorophyte Chlamydomonas reinhardtii, although both organisms are flagellate unicells. Thus, it seems likely that several major physiological changes (e.g. in the regulation of photosynthesis and photorespiration) took place early during the evolution of streptophytes, i.e. before the transition to land

A set of genes conserved in sequence and expression traces back the establishment of multicellularity in social amoebae

Background: The developmental cycle of Dictyostelid amoebae represents an early form of multicellularity with cell type differentiation. Mutant studies in the model Dictyostelium discoideum revealed that its developmental program integrates the actions of genes involved in signal transduction, adhesion, motility, autophagy and cell wall and matrix biosynthesis. However, due to functional redundancy and fail safe options not required in the laboratory, this single organism approach cannot capture all essential genes. To understand how multicellular organisms evolved, it is essential to recognize both the conserved core features of their developmental programs and the gene modifications that instigated phenotypic innovation. For complex organisms, such as animals, this is not within easy reach, but it is feasible for less complex forms, such as the Dictyostelid social amoebas. Results: We compared global profiles of gene expression during the development of four social amoebae species that represent 600 mya of Dictyostelia evolution, and identified orthologous conserved genes with similar developmental up-regulation of expression using three different methods. For validation, we disrupted five genes of this core set and examined the phenotypic consequences. Conclusion: At least 71 of the developmentally regulated genes that were identified with all methods were likely to be already present in the last ancestor of all Dictyostelia. The lack of phenotypic changes in null mutants indicates that even highly conserved genes either participate in functionally redundant pathways or are necessary for developmental progression under adverse, non-standard laboratory conditions. Both mechanisms provide robustness to the developmental program, but impose a limit on the information that can be obtained from deleting single genes

Comparative gene expression in toxic versus non-toxic strains of the marine dinoflagellate Alexandrium minutum

Yang I, John U, Beszteri S, et al. Comparative gene expression in toxic versus non-toxic strains of the marine dinoflagellate Alexandrium minutum. BMC Genomics. 2010;11(1): 248.Background The dinoflagellate Alexandrium minutum typically produces paralytic shellfish poisoning (PSP) toxins, which are known only from cyanobacteria and dinoflagellates. While a PSP toxin gene cluster has recently been characterized in cyanobacteria, the genetic background of PSP toxin production in dinoflagellates remains elusive. Results We constructed and analysed an expressed sequence tag (EST) library of A. minutum, which contained 15,703 read sequences yielding a total of 4,320 unique expressed clusters. Of these clusters, 72% combined the forward-and reverse reads of at least one bacterial clone. This sequence resource was then used to construct an oligonucleotide microarray. We analysed the expression of all clusters in three different strains. While the cyanobacterial PSP toxin genes were not found among the A. minutum sequences, 192 genes were differentially expressed between toxic and non-toxic strains. Conclusions Based on this study and on the lack of identified PSP synthesis genes in the two existent Alexandrium tamarense EST libraries, we propose that the PSP toxin genes in dinoflagellates might be more different from their cyanobacterial counterparts than would be expected in the case of a recent gene transfer. As a starting point to identify possible PSP toxin-associated genes in dinoflagellates without relying on a priori sequence information, the sequences only present in mRNA pools of the toxic strain can be seen as putative candidates involved in toxin synthesis and regulation, or acclimation to intracellular PSP toxins

Origin of land plants: Do conjugating green algae hold the key?

<p>Abstract</p> <p>Background</p> <p>The terrestrial habitat was colonized by the ancestors of modern land plants about 500 to 470 million years ago. Today it is widely accepted that land plants (embryophytes) evolved from streptophyte algae, also referred to as charophycean algae. The streptophyte algae are a paraphyletic group of green algae, ranging from unicellular flagellates to morphologically complex forms such as the stoneworts (Charales). For a better understanding of the evolution of land plants, it is of prime importance to identify the streptophyte algae that are the sister-group to the embryophytes. The Charales, the Coleochaetales or more recently the Zygnematales have been considered to be the sister group of the embryophytes However, despite many years of phylogenetic studies, this question has not been resolved and remains controversial.</p> <p>Results</p> <p>Here, we use a large data set of nuclear-encoded genes (129 proteins) from 40 green plant taxa (Viridiplantae) including 21 embryophytes and six streptophyte algae, representing all major streptophyte algal lineages, to investigate the phylogenetic relationships of streptophyte algae and embryophytes. Our phylogenetic analyses indicate that either the Zygnematales or a clade consisting of the Zygnematales and the Coleochaetales are the sister group to embryophytes.</p> <p>Conclusions</p> <p>Our analyses support the notion that the Charales are not the closest living relatives of embryophytes. Instead, the Zygnematales or a clade consisting of Zygnematales and Coleochaetales are most likely the sister group of embryophytes. Although this result is in agreement with a previously published phylogenetic study of chloroplast genomes, additional data are needed to confirm this conclusion. A Zygnematales/embryophyte sister group relationship has important implications for early land plant evolution. If substantiated, it should allow us to address important questions regarding the primary adaptations of viridiplants during the conquest of land. Clearly, the biology of the Zygnematales will receive renewed interest in the future.</p