The reduced kinome of Ostreococcus tauri: core eukaryotic signalling components in a tractable model species

Abstract

BackgroundThe current knowledge of eukaryote signalling originates from phenotypically diverse organisms. There is a pressing need to identify conserved signalling components among eukaryotes, which will lead to the transfer of knowledge across kingdoms. Two useful properties of a eukaryote model for signalling are (1) reduced signalling complexity, and (2) conservation of signalling components. The alga Ostreococcus tauri is described as the smallest free-living eukaryote. With less than 8,000 genes, it represents a highly constrained genomic palette.ResultsOur survey revealed 133 protein kinases and 34 protein phosphatases (1.7% and 0.4% of the proteome). We conducted phosphoproteomic experiments and constructed domain structures and phylogenies for the catalytic protein-kinases. For each of the major kinases families we review the completeness and divergence of O. tauri representatives in comparison to the well-studied kinomes of the laboratory models Arabidopsis thaliana and Saccharomyces cerevisiae, and of Homo sapiens. Many kinase clades in O. tauri were reduced to a single member, in preference to the loss of family diversity, whereas TKL and ABC1 clades were expanded. We also identified kinases that have been lost in A. thaliana but retained in O. tauri. For three, contrasting eukaryotic pathways – TOR, MAPK, and the circadian clock – we established the subset of conserved components and demonstrate conserved sites of substrate phosphorylation and kinase motifs.ConclusionsWe conclude that O. tauri satisfies our two central requirements. Several of its kinases are more closely related to H. sapiens orthologs than S. cerevisiae is to H. sapiens. The greatly reduced kinome of O. tauri is therefore a suitable model for signalling in free-living eukaryotes.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-640) contains supplementary material, which is available to authorized users.

Marine Prasinoviruses and Their Tiny Plankton Hosts: A Review

“…These include its cellular simplicity (haploid with just a single mitochondrion, chloroplast and Golgi body, no cell wall or motility apparatus e.g., flagella). Ostreococcus , unlike Micromonas , is not flagellated and unlike Bathycoccus does not have scales or liths on the outside of the cell); its phylogenetic positioning as an early-diverging green plant lineage [26,27]; ease of keeping in culture; successful genetic transformation [45]; availability of four complete fully annotated genomes [30,31,32,33]; complete mitochondrial and chloroplast genomes available for O. tauri [46] and proteome analysis [62,63]. Ostreococcus has emerged as an ideal model organism in studies of signalling in eukaryotic cells [64] and light and circadian clocks or oscillators [65,66,67].…”

Circadian protein regulation in the green lineage I. A phospho-dawn of protein modification anticipates light onset in the picoeukaryoteO. tauri

“…Phosphorylation of an existing protein is inexpensive in comparison, occurs rapidly and may then alter protein activity through conformational change or intermolecular recognition [7]. A set of protein kinase families, along with functions such as cell cycle control, are 60 conserved among eukaryotes [8]. ~1000 protein kinases shape the phosphoproteome in Arabidopsis [9] including several in plastids [10], compared to 518 in human [11].…”

Functional characterization of Ostreococcus tauri phototropin

“…At least 21 in vivo phosphorylation sites have been identified for Atphot1 by liquid chromatography mass spectrometry (Christie et al ., ). By contrast, only one phosphorylation site has been reported so far for Otphot, which corresponds to S171 within the LOV‐linker sequence (Hindle et al ., ). The reduced level of autophosphorylation in algal phots may account for the absence of an electrophoretic mobility shift for Otphot when expressed in Arabidopsis (Fig.…”