Molecular characterization of bacteria and kleptoplast within Virgulinella fragilis

Abstrac

A phylogenetic mosaic plastid proteome and unusual plastid-targeting signals in the green-colored dinoflagellate Lepidodinium chlorophorum

Background Plastid replacements through secondary endosymbioses include massive transfer of genes from the endosymbiont to the host nucleus and require a new targeting system to enable transport of the plastid-targeted proteins across 3-4 plastid membranes. The dinoflagellates are the only eukaryotic lineage that has been shown to have undergone several plastid replacement events, and this group is thus highly relevant for studying the processes involved in plastid evolution. In this study, we analyzed the phylogenetic origin and N-terminal extensions of plastid-targeted proteins from Lepidodinium chlorophorum, a member of the only dinoflagellate genus that harbors a green secondary plastid rather than the red algal-derived, peridinin-containing plastid usually found in photosynthetic dinoflagellates. Results We sequenced 4,746 randomly picked clones from a L. chlorophorum cDNA library. 22 of the assembled genes were identified as genes encoding proteins functioning in plastids. Some of these were of green algal origin. This confirms that genes have been transferred from the plastid to the host nucleus of L. chlorophorum and indicates that the plastid is fully integrated as an organelle in the host. Other nuclear-encoded plastid-targeted protein genes, however, are clearly not of green algal origin, but have been derived from a number of different algal groups, including dinoflagellates, streptophytes, heterokonts, and red algae. The characteristics of N-terminal plastid-targeting peptides of all of these genes are substantially different from those found in peridinin-containing dinoflagellates and green algae. Conclusions L. chlorophorum expresses plastid-targeted proteins with a range of different origins, which probably arose through endosymbiotic gene transfer (EGT) and horizontal gene transfer (HGT). The N-terminal extension of the genes is different from the extensions found in green alga and other dinoflagellates (peridinin- and haptophyte plastids). These modifications have likely enabled the mosaic proteome of L. chlorophorum

Algivore or phototroph?: Plakobranchus ocellatus (Gastropoda) continuously acquires kleptoplasts and nutrition from multiple algal species in nature

The sea slug Plakobranchus ocellatus (Sacoglossa, Gastropoda) retains photosynthetically active chloroplasts from ingested algae (functional kleptoplasts) in the epithelial cells of its digestive gland for up to 10 months. While its feeding behavior has not been observed in natural habitats, two hypotheses have been proposed: 1) adult P. ocellatus uses kleptoplasts to obtain photosynthates and nutritionally behaves as a photoautotroph without replenishing the kleptoplasts; or 2) it behaves as a mixotroph (photoautotroph and herbivorous consumer) and replenishes kleptoplasts continually or periodically. To address the question of which hypothesis is more likely, we examined the source algae for kleptoplasts and temporal changes in kleptoplast composition and nutritional contribution. By characterizing the temporal diversity of P. ocellatus kleptoplasts using rbcL sequences, we found that P. ocellatus harvests kleptoplasts from at least 8 different siphonous green algal species, that kleptoplasts from more than one species are present in each individual sea slug, and that the kleptoplast composition differs temporally. These results suggest that wild P. ocellatus often feed on multiple species of siphonous algae from which they continually obtain fresh chloroplasts. By estimating the trophic position of wild and starved P. ocellatus using the stable nitrogen isotopic composition of amino acids, we showed that despite the abundance of kleptoplasts, their photosynthates do not contribute greatly to the nutrition of wild P. ocellatus, but that kleptoplast photosynthates form a significant source of nutrition for starved sea slugs. The herbivorous nature of wild P. ocellatus is consistent with insights from molecular analyses indicating that kleptoplasts are frequently replenished from ingested algae, leading to the conclusion that natural populations of P. ocellatus do not rely on photosynthesis but mainly on the digestion of ingested algae

Lateral transfer of tetrahymanol-synthesizing genes has allowed multiple diverse eukaryote lineages to independently adapt to environments without oxygen

Sterols are key components of eukaryotic cellular membranes that are synthesized by multi-enzyme pathways that require molecular oxygen. Because prokaryotes fundamentally lack sterols, it is unclear how the vast diversity of bacterivorous eukaryotes that inhabit hypoxic environments obtain, or synthesize, sterols. Here we show that tetrahymanol, a triterpenoid that does not require molecular oxygen for its biosynthesis, likely functions as a surrogate of sterol in eukaryotes inhabiting oxygen-poor environments. Genes encoding the tetrahymanol synthesizing enzyme squalene-tetrahymanol cyclase were found from several phylogenetically diverged eukaryotes that live in oxygen-poor environments and appear to have been laterally transferred among such eukaryotes

A Hypothesis for the Evolution of Nuclear-Encoded, Plastid-Targeted Glyceraldehyde-3-Phosphate Dehydrogenase Genes in “Chromalveolate” Members

Eukaryotes bearing red alga-derived plastids — photosynthetic alveolates (dinoflagellates plus the apicomplexan Toxoplasma gondii plus the chromerid Chromera velia), photosynthetic stramenopiles, haptophytes, and cryptophytes — possess unique plastid-targeted glyceraldehyde-3-phosphate dehydrogenases (henceforth designated as “GapC1”). Pioneering phylogenetic studies have indicated a single origin of the GapC1 enzymes in eukaryotic evolution, but there are two potential idiosyncrasies in the GapC1 phylogeny: Firstly, the GapC1 tree topology is apparently inconsistent with the organismal relationship among the “GapC1-containing” groups. Secondly, four stramenopile GapC1 homologues are consistently paraphyletic in previously published studies, although these organisms have been widely accepted as monophyletic. For a closer examination of the above issues, in this study GapC1 gene sampling was improved by determining/identifying nine stramenopile and two cryptophyte genes. Phylogenetic analyses of our GapC1 dataset, which is particularly rich in the stramenopile homologues, prompt us to propose a new scenario that assumes multiple, lateral GapC1 gene transfer events to explain the incongruity between the GapC1 phylogeny and the organismal relationships amongst the “GapC1-containing” groups. Under our new scenario, GapC1 genes uniquely found in photosynthetic alveolates, photosynthetic stramenopiles, haptophytes, and cryptopyhytes are not necessarily a character vertically inherited from a common ancestor

渦鞭毛藻類の核および葉緑体遺伝子の分子系統解析 : 渦鞭毛藻類の葉緑体の起源に関する考察

京都大学0048新制・課程博士博士(農学)甲第8563号農博第1146号新制||農||809(附属図書館)学位論文||H12||N3442(農学部図書室)UT51-2000-M27京都大学大学院農学研究科応用生物科学専攻(主査)教授 内田 有恆, 教授 中原 紘之, 教授 大山 莞爾学位規則第4条第1項該当Doctor of Agricultural ScienceKyoto UniversityDA

Anucleated cryptophyte endosymbionts in the gonyaulacalean dinoflagellates, Amylax buxus and Amylax triacantha (Dinophyceae)

Cryptophyte endosymbionts, suffering selective digestion of nuclei, were found in gonyaulacalean dinoflagellates, Amylax buxus (Balech) Dodge and Amylax triacantha (Jörgensen) Sournia. They emitted bright yellow-orange fluorescence (= 590 nm emission) under epifluorescent microscopy and possessed U-shape plastids. Under transmission electron microscopy, the plastid was characterized with loose arrangement of two to three thylakoids stacks and with stalked pyrenoid, all coincide to those of cryptophyte genus Teleaulax. Indeed, molecular data based on plastid small subunit rRNA gene demonstrated that the endosymbionts in Amylax are originated from Teleaulax amphioxeia. The stolen plastid (kleptoplastids) in Dinophysis is also acquired from this cryptophyte species. However, in sharp contrast to the case of Dinophysis, the plastid of endosymbiont in Amylax was surrounded by double layer of plastid endoplasmic reticulum, and within the periplastidal area, nucleomorph was retained. The endosymbionts also possessed mitochondria with characteristic plate-like cristae, but lost cell-surface structure. Dinoflagellate's phagocytotic membrane seemed to surround the endosymbionts right after the incorporation, but the membrane itself would probably be digested eventually. Remarkedly, only one cryptophyte cell among 14 endosymbionts in a cell of A. buxus had a nucleus. This is a first finding of kleptoplastidy in gonyaulacalean dinoflagellates, and provides unique strategy of a dinoflagellate in which it selectively eliminate the endosymbiont nucleus

Uncovering sibling species in Radiolaria: Evidence for ecological partitioning in a marine planktonic protist

Phylogeography of unicellular plankton, as representative pelagic organisms, is fundamental to understanding their evolution in the ocean. Historically, these microplankton were believed to have cosmopolitan distributions achieved through passive transport and little potential for speciation because of a lack of geographic barriers in the oceans. Recent phylogeographic studies of these microplankton, however, have often revealed high diversity and fine-scale geographic distributions. These apparent contradictions may result from poor knowledge of the spatial distributions of pelagic microplankton in the water column. More information about both geographic and vertical distributions of pelagic populations could reveal the dispersal pathways, gene flow, and resulting diversifications in the open ocean. Here we demonstrate that two genetic types of the radiolarian morphospecies Spongotrochus glacialis with morphological differences are vertically segregated into the upper and lower surface waters within the pycnocline of the North Pacific Subtropical Water. This vertically separated distribution of two sister species is associated with distinct ecological partitioning. These two species could survive on different food resources from their respective environments: one in oligotrophic surface waters by using nutrients from symbionts, and the other at greater depths by depending on both heterotrophic and symbiotic nutrition. Moreover, molecular divergence-time estimates suggest that the two species diverged during the period of oligotrophic surface-water development in the Pacific Ocean. Our findings suggest that genetic isolation in the vertical dimension occurs through ecological partitioning even in the absence of physical barriers in the pelagic oceans