Odontella Sinensis Research Articles

Fucoxanthin: a marine carotenoid has anticancer activities and apoptosis-inducing effect (a review)

Fucoxanthin, a natural xanthophyll carotenoid, is generally found in brown seaweeds, such as Sargassum duplicatum, Turbinaria turbinata, Padina australis, Undaria pinnatifida, and Laminaria japonica; and microalga or diatom such as Phaeodactylum tricornutum, Isochrysis galbana and Odontella sinensis. Fucoxanthin is a marine xanthophyll exhibiting several anticancer activities, such as anticancer activities against leukemia, prostate, cervical, hepatoma, colon, and lung cancer. Cancer disease is frequently considered to be a disease of the cell cycle. Then, apoptosis is a dominant form of cell death with particular relevance to cancer, characterized initially by a series of stereotypic morphological changes, such as condensation and fragmentation of chromatin shrinking of cytoplasmic (cell shrinkage), a decrease in cell volume and alterations to the plasma membrane, mitochondrial depolarization, membrane blebbing, and cell packaging into apoptotic bodies or formation of apoptotic bodies. In general, there are four techniques for the detection of apoptosis, namely: (1). morphological changes analysis using an inverted microscope, scanning electron microscope, fluorescent microscope, (2) gel electrophoresis, (3). immunohistochemistry (e.g., analysis of caspase-3), and (4) flow cytometry.

Interaction of a dinoflagellate neurotoxin with voltage-activated ion channels in a marine diatom.

BackgroundThe potent neurotoxins produced by the harmful algal bloom species Karenia brevis are activators of sodium voltage-gated channels (VGC) in animals, resulting in altered channel kinetics and membrane hyperexcitability. Recent biophysical and genomic evidence supports widespread presence of homologous sodium (Na+) and calcium (Ca2+) permeable VGCs in unicellular algae, including marine phytoplankton. We therefore hypothesized that VGCs of these phytoplankton may be an allelopathic target for waterborne neurotoxins produced by K. brevis blooms that could lead to ion channel dysfunction and disruption of signaling in a similar manner to animal Na+ VGCs.MethodsWe examined the interaction of brevetoxin-3 (PbTx-3), a K. brevis neurotoxin, with the Na+/Ca2+ VGC of the non-toxic diatom Odontella sinensis using electrophysiology. Single electrode current- and voltage- clamp recordings from O. sinensis in the presence of PbTx-3 were used to examine the toxin’s effect on voltage gated Na+/Ca2+ currents. In silico analysis was used to identify the putative PbTx binding site in the diatoms. We identified Na+/Ca2+ VCG homologs from the transcriptomes and genomes of 12 diatoms, including three transcripts from O. sinensis and aligned them with site-5 of Na+ VGCs, previously identified as the PbTx binding site in animals.ResultsUp to 1 µM PbTx had no effect on diatom resting membrane potential or membrane excitability. The kinetics of fast inward Na+/Ca2+ currents that underlie diatom action potentials were also unaffected. However, the peak inward current was inhibited by 33%, delayed outward current was inhibited by 25%, and reversal potential of the currents shifted positive, indicating a change in permeability of the underlying channels. Sequence analysis showed a lack of conservation of the PbTx binding site in diatom VGC homologs, many of which share molecular features more similar to single-domain bacterial Na+/Ca2+ VGCs than the 4-domain eukaryote channels.DiscussionAlthough membrane excitability and the kinetics of action potential currents were unaffected, the permeation of the channels underlying the diatom action potential was significantly altered in the presence of PbTx-3. However, at environmentally relevant concentrations the effects of PbTx- on diatom voltage activated currents and interference of cell signaling through this pathway may be limited. The relative insensitivity of phytoplankton VGCs may be due to divergence of site-5 (the putative PbTx binding site), and in some cases, such as O. sinensis, resistance to toxin effects may be because of evolutionary loss of the 4-domain eukaryote channel, while retaining a single domain bacterial-like VGC that can substitute in the generation of fast action potentials.

Dynamic changes in carbonate chemistry in the microenvironment around single marine phytoplankton cells

Photosynthesis by marine diatoms plays a major role in the global carbon cycle, although the precise mechanisms of dissolved inorganic carbon (DIC) uptake remain unclear. A lack of direct measurements of carbonate chemistry at the cell surface has led to uncertainty over the underlying membrane transport processes and the role of external carbonic anhydrase (eCA). Here we identify rapid and substantial photosynthesis-driven increases in pH and [CO32−] primarily due to the activity of eCA at the cell surface of the large diatom Odontella sinensis using direct simultaneous microelectrode measurements of pH and CO32− along with modelling of cell surface inorganic carbonate chemistry. Our results show that eCA acts to maintain cell surface CO2 concentrations, making a major contribution to DIC supply in O. sinensis. Carbonate chemistry at the cell surface is therefore highly dynamic and strongly dependent on cell size, morphology and the carbonate chemistry of the bulk seawater.

Antioxidant capacities of fucoxanthin-producing algae as influenced by their carotenoid and phenolic contents

Natural antioxidants from sustainable sources are favoured to accommodate worldwide antioxidant demand. In addition to bioprospecting for natural and sustainable antioxidant sources, this study aimed to investigate the relationship between the bioactives (i.e. carotenoid and phenolic acids) and the antioxidant capacities in fucoxanthin‐producing algae. Total carotenoid, phenolic acid, fucoxanthin contents and fatty acid profile of six species of algae (five microalgae and one macroalga) were quantified followed by bioactivity evaluation using four antioxidant assays. Chaetoceros calcitrans and Isochrysis galbana displayed the highest antioxidant activity, followed by Odontella sinensis and Skeletonema costatum which showed moderate bioactivities. Phaeodactylum tricornutum and Saccharina japonica exhibited the least antioxidant activities amongst the algae species examined. Pearson correlation and multiple linear regression showed that both carotenoids and phenolic acids were significantly correlated (p<0.05) with the antioxidant activities, indicating the influence of these bioactives on the algal antioxidant capacities.

Heterotrophic flagellates increase microalgal biomass yield

In time of scarcity of fossil energies, microalgae are attracting interest as a potential source of renewable energy due to their high growth rates and potential high lipid contents. Additionally, cultivation may be an abatement measure to remove surplus nutrients from eutrophicated ecosystems. At present, microalgal cultivations for biomass production are run mainly in monocultures, which are easily contaminated with competing microalgae or grazers. Furthermore, heterotrophic bacteria are highly abundant and may strongly reduce the yield in the target microalgae through competition for nutrients. In three laboratory experiments, we tested whether heterotrophic flagellates (Oxyrrhis marina and Cafeteria roenbergensis) can make nutrients bound in bacteria available for marine diatoms (Coscinodiscus granii and Odontella sinensis) and can shift the competition for inorganic nutrients towards the microalgae. Cultures were run with and without flagellates, under different conditions: without an external carbon source, in presence of organic matter (barley grains) or biogas wastewater. The presence of flagellates had a positive effect on microalgal growth, but this was context and species specific. The presence of the flagellates affected the maximum algal growth rates (r) especially in Coscinodiscus granii. A maximal biomass increase (29.93 ± 2.98 %) (mean ± standard deviation, n = 3) was observed for Coscinodiscus granii in F/2 + Si medium. Furthermore, although the flagellates were attributed to the detrital fraction, their presence resulted in a significant reduction of detritus. In conclusion, heterotrophic flagellates have the potential to increase nutrient use efficiency especially in algae bioreactors with slow-growing large phytoplankton taxa. This effect may be particularly relevant in organic polluted water.

La condición ecológica de la bahía de Tumaco (Pacífico colombiano): evaluación de la calidad del agua y del fitoplancton

The Bay of Tumaco has a strong interaction between waters discharged from different rivers, the rivers beds are characterized by being short but mighty, and the waters of oceanic origin projecting towards the coast, a situation that creates permanent variability of the physicochemical conditions that may be accentuated or attenuated according to the tidal cycle and the climatic seasons. Under these considerations, we characterized the phytoplankton community of the Bay waters in high and low tide in two seasons of the year and related them to physicochemical variables to assess the ecological condition of the Bay. Sampling was conducted in April (rainy season) and August (dry season) in nine stations. From the analysis of species composition and abundance, using a non-metric multidimensional scaling (nMDS), there were significant differences in the composition and abundance between the two seasons of the year (p = 0.001), showing less abundance, more species richness, uniformity and diversity in the rainy season compared to the dry season. Seasonal fluctuations in SST, salinity, chlorophyll a, nitrites and nitrates (Spearman's rank correlation coefficient: 0.545, p = 0.001), were associated with biological pattern found. These conditions favored the growth of Rhizosolenia imbricata, Odontella sinensis, Guinardia striata, Scrippsiella sp. and Protoperidinium sp. in rainy season and Coscinodiscus Granni, Leptocylindricus danicus, Thalassiosira sp., Astrionella japónica and Skeletonema costatum in the dry season. Comparison with other tropical estuaries physicochemical characteristics and the community structure it can be inferred that the ecological condition of the Bay is good, but is vulnerable to changes in its environmental conditions. It can be inferred that this estuary has the ability, at least in short spatial and temporal scales, to assimilate nutrient inputs, so algal blooms are rare.

Phytoplankton of a dynamic Amazon sandy beach

Costa, R.M. da, Matos, J.B., Pinto, K.S.T., Pereira, L.C.C., 2013. Phytoplankton of a dynamic Amazon sandy beachThe present study was developed to characterize the structure and the temporal variation of the phytoplankton of the surf zone of Atalaia beach (Pará, Brazil) and to investigate the effect of certain environmental variables on this community. Nyctemeral sampling was carried out in November/08, March/09, June/09 and September/09. Ninety- eight taxa were identified. The diatoms dominated the local microphytoplankton with the species Coscinodiscus perforatus Ehrenberg, Dimeregramma minor (Gregory) Ralfs, Ditylum brightwellii (West) Grunow and Odontella sinensis (Greville) Grunow having the highest frequency of occurrence and relative abundance. The maximum phytoplankton density was 1,723 ± 257 ×103 cell L−1 in September/09 (F=18.8; p <0.05), while biomass (chlorophyll-a content) was significantly higher in November/08 (U= 0.00; p <0.05). The highest densities of D. minor in September resulted in the lowest observed diversity and evenness. Cluster Analysis showed the formation of three groups, with 55% similarity. The separation of the groups was influenced primarily by the seasonal distribution of samples. Overall, rainfall and consequently variation in salinity showed a strong influence on local phytoplankton composition, density and biomass. Furthermore, the strong local hydrodynamics, as well as the action of the winds and currents promoted the ressuspension of tychoplankton species that characterized the structure of the local phytoplankton.

A Fast Na+/Ca2+-Based Action Potential in a Marine Diatom

BackgroundElectrical impulses in animals play essential roles in co-ordinating an array of physiological functions including movement, secretion, environmental sensing and development. Underpinning many of these electrical signals is a fast Na+-based action potential that has been fully characterised only in cells associated with the neuromuscular systems of multicellular animals. Such rapid action potentials are thought to have evolved with the first metazoans, with cnidarians being the earliest representatives. The present study demonstrates that a unicellular protist, the marine diatom Odontella sinensis, can also generate a fast Na+/Ca2+ based action potential that has remarkably similar biophysical and pharmacological properties to invertebrates and vertebrate cardiac and skeletal muscle cells.Methodology/Principal FindingsThe kinetic, ionic and pharmacological properties of the rapid diatom action potential were examined using single electrode current and voltage clamp techniques. Overall, the characteristics of the fast diatom currents most closely resemble those of vertebrate and invertebrate muscle Na+/Ca2+ currents.Conclusions/SignificanceThis is the first demonstration of voltage-activated Na+ channels and the capacity to generate fast Na+-based action potentials in a unicellular photosynthetic organism. The biophysical and pharmacological characteristics together with the presence of a voltage activated Na+/Ca2+ channel homologue in the recently sequenced genome of the diatom Thalassiosira pseudonana, provides direct evidence supporting the hypothesis that this rapid signalling mechanism arose in ancestral unicellular eukaryotes and has been retained in at least two phylogenetically distant lineages of eukaryotes; opisthokonts and the stramenopiles. The functional role of the fast animal-like action potential in diatoms remains to be elucidated but is likely involved in rapid environmental sensing of these widespread and successful marine protists.

New phytoplankton species in the Bay of Fundy since 1995

Abstract Martin, J. L., and LeGresley, M. M. 2008. New phytoplankton species in the Bay of Fundy since 1995. – ICES Journal of Marine Science, 65: 759–764. A monitoring programme was initiated in 1987 to study phytoplankton populations in the Western Isles region of the Bay of Fundy, southwest New Brunswick. Samples are collected weekly from May through October, and monthly during the remaining months, to determine phytoplankton distribution and abundance at Brandy Cove, Lime Kiln Bay, Deadmans Harbour, the Wolves Islands, and mid-Passamaquoddy Bay. Since the programme was initiated, several previously absent or non-indigenous species have been found, suggesting that new species may have been introduced to the area. In order to establish a baseline for species indigenous to Bay of Fundy waters, we have taken a conservative approach and termed species reported for the first time in the Bay of Fundy system since 1995 as “new” species. New species include the following: (dinoflagellates) Alexandrium pseudogonyaulax, Amphidinium carterae, A. sphenoides, Ceratium macroceros, Polykrikos schwartzii, Preperidinium meunieri, Protoperidinium crassipes, and Pyrocystis lunata; (diatoms) Attheya septentrionalis, Attheya longicornis, Chaetoceros radicans, Cylindrotheca gracilis, Grammatophora serpentina, Lithodesmium undulatum, Mediopyxis helysia, Membraneis challengeri, Neodenticula seminae, Odontella sinensis, Proboscia eumorpha, Pseudo-nitzschia subpacifica, Pseudo-nitzschia fraudulenta, and Thalassiosira punctigera.

Chloroplast genomes of the diatoms Phaeodactylum tricornutum and Thalassiosira pseudonana: comparison with other plastid genomes of the red lineage

The chloroplast genomes of the pennate diatom Phaeodactylum tricornutum and the centric diatom Thalassiosira pseudonana have been completely sequenced and are compared with those of other secondary plastids of the red lineage: the centric diatom Odontella sinensis, the haptophyte Emiliania huxleyi, and the cryptophyte Guillardia theta. All five chromist genomes are compact, with small intergenic regions and no introns. The three diatom genomes are similar in gene content with 127-130 protein-coding genes, and genes for 27 tRNAs, three ribosomal RNAs and two small RNAs (tmRNA and signal recognition particle RNA). All three genomes have open-reading frames corresponding to ORFs148, 355 and 380 of O. sinensis, which have been assigned the names ycf88, ycf89 and ycf90. Gene order is not strictly conserved, but there are a number of conserved gene clusters showing remnants of red algal origin. The acpP, tsf and psb28 genes appear to be on the way from the plastid to the host nucleus, indicating that endosymbiotic gene transfer is a continuing process.

A Phytophthora sojae gene of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) induced in host infection and its anti-oxidative function in yeast

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a multifunctional protein well defined in eukaryotes, especially in mammalian and Saccharomyces cerevisiae. Using the method of suppression subtractive hybridization (SSH), we identified a Phytophthora sojae cDNA coding GAPDH, which was up-regulated during the early stage of soybean infection. The termed PsGapdh gene possessed three copies in the P. sojae genome. Its amino acid sequence harbored overall conserved domain of GADPH, homologous closest to GapC1 of Achlya bisexualis (oomycete) and adjoined to GapC2s of Odontella sinensis and Phaeodactylum tricornutum (diatom), on the C-II branch of subfamily GapC in phylogeny tree of GAPDH. The transcriptional level of PsGapdh was up-regulated throughout early infection. Heterogenous expression of PsGapdh in the yeast tdh1-deleted mutant could rescue growth arrest under continuous exposure to H2O2. These results indicated active roles of PsGapdh in pathogen-host interaction and anti-oxidation.

The peculiar distribution of class I and class II aldolases in diatoms and in red algae

Diatom plastids probably evolved by secondary endocytobiosis from a red alga that was up by a eukaryotic host cell. Apparently, this process increased the complexity of the intracellular distribution of metabolic enzymes. We identified genes encoding fructose-bisphosphate aldolases (FBA) in two centric (Odontella sinensis, Thalassiosira pseudonana) and one pennate (Phaeodactylum tricornutum) diatoms and found that four different aldolases are present in both groups: two plastid targeted class II enzymes (FBAC1 and FBAC2), one cytosolic class II (FBA3) and one cytosolic class I (FBA4) enzyme. The pennate Phaeodactylum possesses an additional plastidic class I enzyme (FBAC5). We verified the classification of the different aldolases in the diatoms by enzymatic characterization of isolated plastids and whole cell extracts. Interestingly, our results imply that in plastids of centric and pennate diatoms mainly either class I or class II aldolases are active. We also identified genes for both class I and class II aldolases in red algal EST databases, thus presenting a fascinating example of the reutilization and recompartmentalization of different aldolase isoenzymes during secondary endocytobiosis but as well demonstrating the limited use of metabolic enzymes as markers for the interpretation of phylogenetic histories in algae.

Diatom plastids possess a phosphoribulokinase with an altered regulation and no oxidative pentose phosphate pathway.

The chloroplast enzyme phosphoribulokinase (PRK; EC 2.7.1.19) is part of the Calvin cycle (reductive pentose phosphate pathway) responsible for CO(2) fixation in photosynthetic organisms. In green algae and vascular plants, this enzyme is light regulated via reversible reduction by reduced thioredoxin. We have sequenced and characterized the gene of the PRK from the marine diatom Odontella sinensis and found that the enzyme has the conserved cysteine residues necessary for thioredoxin-dependent regulation. Analysis of enzymatic activity of partially purified diatom enzyme and of purified protein obtained by native overexpression in Escherichia coli, however, revealed that under natural redox conditions the diatom enzyme is generally active. Treatment of the enzyme with strong oxidants results in inhibition of the enzyme, which is reversible by subsequent incubation with reducing agents. We determined the redox midpoint potentials of the regulatory cysteine in the PRK from O. sinensis in comparison to the respective spinach (Spinacia oleracea) enzyme and found a more positive redox potential for the diatom PRK, indicating that in vivo this enzyme might not be regulated by thioredoxin. We also demonstrate that in protease-treated diatom plastids, activities of enzymes of the oxidative pentose phosphate pathway are not detectable, thus reducing the need for a tight regulation of the Calvin cycle in diatoms. We discuss our results in the context of rearrangements of the subcellular compartmentation of metabolic pathways due to the peculiar evolution of diatoms by secondary endocytobiosis.

Identification of ultraviolet-B responsive genes in the pea, Pisum sativum L.

In the present work, UV-B-repressible and UV-B-inducible genes were identified in the pea, Pisum sativum L., by rapid amplification of 3′ cDNA ends through use of the polymerase chain reaction. Of the UV-B-repressible clones, psUVRub and psUVDeh represent genes encoding Rubisco activase and dehydrin, respectively. A third clone, psUVZinc, did not correspond closely in overall nucleotide sequence to any gene registered in GenBank; however, a short deduced peptide shared similarity with the photosystem-II reaction center X protein of the chlorophyll a+c-containing alga, Odontella sinensis. The UV-B-inducible clones, psUVGluc, psUVAux and psUVRib, were related to genes encoding β-1, 3-glucanase, auxin-repressed protein, and a 40S ribosomal protein, respectively. The modulation of these pea genes indicates how UV-B, through its actions as a physical stressor, affects several important physiological processes in plants.

Phylogenetic analyses of Bolidophyceae (Heterokontophyta) using rbcL gene sequences support their sister group relationship to diatoms

Nearly complete (> 97%) chloroplast-encoded rbcL gene sequences were determined for Bolidomonas mediterranea from the eastern Mediterranean Sea and two strains of B. pacifica var. eleuthera from the equatorial Pacific Ocean. The three sequences were added to an rbcL data matrix comprising 45 taxa representing 11 of the 12 recognized classes of Hetero-kontophyta. Phylogenetic analyses that used maximum parsimony (MP), maximum likelihood (ML) and neighbour-joining (NJ) algorithms supported their sister group relationship to the Bacillariophyceae. Centric and pennate diatoms and the three novel Bolidomonas rbcL sequences share a two-amino-acid insertion at position 1336, relative to the homologous position in the complete sequence for the centric diatom Odontella sinensis. This synapomorphic character state further supports a common evolutionary history of bolidophyceans and diatoms. Chloroplast- and nuclear-encoded molecular markers thus favour the idea that the ancestor of the diatoms possessed two flagella. The Rubisco spacer region was also determined. Sequences showed no differences among the strains of B. pacifica examined but these differed by 25% from B. mediterranea. New observations are presented on the distribution of Bolidomonas and the phylogenetic relationships of bolidomonads and other heterokont algae are discussed.

The GC-rich region and TΨC trn arm found in the petF region of the Thalassiosira weissflogii plastid genome encode a tmRNA

We recently reported (Gueneau et al ., 1998) the existence of a GC-rich region downstream of the trnR gene which was conserved in the plastidial genome of three algae: Thalassiosira weissflogii , Odontella sinensis (Bacillariophyceae) and Porphyra purpurea (Rhodophyceae). We identified this GC-rich region as a possible vestigial ORF and noted additional high similarity to an open reading frame (ORF) in a plastid from a fourth alga, Pavlova lutherii (Haptophyceae); sequence data from P. lutherii did not extend to the TΨC tRNA arm. We now report that this region instead encodes a recently recognized type of RNA known as tmRNA (Fig. 1 A ).

Targeting of proteins into and within the chloroplast

Chloroplasts are semiautonomous organelles that cannot be made de novo. They possess their own DNA, which encodes only a small part of chloroplastic proteins. The nucleotide sequences for ten different chloroplast genomes: liverwort, maize, tobacco, rice, black pine, Euglena, Epifagus, ChloreIla vulgaris, Cyanidum caldarium, Odontella sinensis, Toxoplasma gondii, have been determined (see NCBI, Entrez, Genomes, Database). There are about 130 structural genes in the chloroplast genome, coding for about 100 different proteins (Sugita and Sugiura 1996). Most proteins in chloroplast are encoded by the nuclear genome and synthesised in the cytosol. With the exception of most outer envelope membrane proteins, nuclearencoded chloroplastic proteins are synthesised with N-terminal extension that contains the chloroplast targeting information of these proteins. This Nterminal extension is referred to as a transit peptide (also termed transit sequence) to distinguish it from other sorting signals such as the signal sequence involved in the secretion of protein in prokaryotes. Transit sequence is necessary and sufficient to target a protein to the chloroplast and is removed after translocation by a stromal processing protease. Import is initiated by binding of the precursor protein to proteinaceous receptor localised on the surface of the chloroplast fol lowed by translocation through the outer and inner envelope membranes. Protein transpor t into chloroplast usually requires ATP and GTP for binding and translocation. Sometimes cytosolic factors are required for keeping the precursor soluble and to provide an import competent conformation. Beside the transit sequence there is information present in the protein for proper routing inside the chloroplast. Proteins that have to cross the thylakoid membrane contain a second Nterminal extension behind the transit peptide that is cleaved by a thylakoid processing peptidase. Protein transport and routing inside chloroplast are outlined on Fig. 1. Chloroplasts are structurally complex organelles with three different membranes: the

Protein Transport into “Complex” Diatom Plastids Utilizes Two Different Targeting Signals

The plastids found in diatoms and other chromophytic algae are completely enclosed by four membranes in contrast to chloroplasts of higher plants, which are surrounded by only two membranes. The bipartite targeting sequence of diatom nuclear-encoded plastid proteins contains an endoplasmic reticulum signal sequence and, based on sequence comparison, a transit peptide-like domain similar to that which targets proteins into the plastids of higher plants. By performing heterologous import experiments using the precursor of the gamma subunit of the chloroplast ATPase from the diatom Odontella sinensis we were able to show that protein import into diatom plastids is at least a two-step event. We demonstrate that the first step involves co-translational transport through endoplasmic reticulum membranes and that there is an additional targeting step which is similar to the import of precursor proteins into chloroplasts of higher plants and green algae indicating that the transit peptide-like domain of the diatom precursor is functionally equivalent to the respective targeting signal of higher plants. Our results suggest that the transit peptide depending targeting mechanism in plastids has apparently remained relatively unchanged over the course of evolution, with only the peptidase cleavage site significantly modified.

The petF region of the chloroplast genome from the diatom Thalassiosira weissflogii: sequence, organization and phylogeny

We report the cloning and characterization of a 1881 bp Thalassiosira weissflogii (Bacillariophyceae, Centrales) plastid genomic fragment containing the ferredoxin gene (petF) and several other genes. The organization of this fragment is exactly the same as its equivalent region from the plastid genome of another centric diatom, Odontella sinensis, and the sequences share high homology in both coding and non-coding regions. Traces of a probable vestigial protein-coding gene and of a partial trn gene are found just after the trnR gene in both diatoms as well as in the plastid genome of the red alga Porphyra purpurea, illustrating the close relationship between red algal and heterokont algal plastid genomes and arguing in favour of the origin of the latter by secondary endosymbiosis. In accordance with phylogenetic analyses of most plastid genes, phylogenetic trees inferred from 69 ferredoxin sequences show that both the green and the red algal plastid genes arose from cyanobacterial genes; our results furthermore suggest that each of these plastid lineages is related to different extant cyanobacterial genes, implying either that different endosymbiotic events were responsible for the origin of green and red plastids or that each lineage kept only one (and a different one) of several paralogous cyanobacterial genes present in the ancestral cyanobacterial genome.

The petF region of the chloroplast genome from the diatom Thalassiosira weissflogii: sequence, organization and phylogeny

We report the cloning and characterization of a 1881 bp Thalassiosira weissflogii (Bacillariophyceae, Centrales) plastid genomic fragment containing the ferredoxin gene (petF) and several other genes. The organization of this fragment is exactly the same as its equivalent region from the plastid genome of another centric diatom, Odontella sinensis, and the sequences share high homology in both coding and non-coding regions. Traces of a probable vestigial protein-coding gene and of a partial trn gene are found just after the trnR gene in both diatoms as well as in the plastid genome of the red alga Porphyra purpurea, illustrating the close relationship between red algal and heterokont algal plastid genomes and arguing in favour of the origin of the latter by secondary endosymbiosis. In accordance with phylogenetic analyses of most plastid genes, phylogenetic trees inferred from 69 ferredoxin sequences show that both the green and the red algal plastid genes arose from cyanobacterial genes; our results furthermore suggest that each of these plastid lineages is related to different extant cyanobacterial genes, implying either that different endosymbiotic events were responsible for the origin of green and red plastids or that each lineage kept only one (and a different one) of several paralogous cyanobacterial genes present in the ancestral cyanobacterial genome.