Heavy metal pollution is an increasing global concern. Among heavy metals, mercury (Hg) is especially dangerous because of its massive release into the environment and high toxicity, especially for aquatic organisms. The molecular response mechanisms of algae to Hg exposure are mostly unknown. Here, we combine physiological, biochemical, and transcriptomic analysis to provide, for the first time, a comprehensive view on the pathways activated in Chromera velia in response to toxic levels of Hg. Production of hydrogen peroxide and superoxide anion, two reactive oxygen species (ROS), showed opposite patterns in response to Hg2+ while reactive nitrogen species (RNS) levels did not change. A deep RNA sequencing analysis generated a total of 307,738,790 high-quality reads assembled in 122,874 transcripts, representing 89,853 unigenes successfully annotated in databases. Detailed analysis of the differently expressed genes corroborates the biochemical results observed in ROS production and suggests novel putative molecular mechanisms in the algal response to Hg2+. Moreover, we indicated that important transcription factor (TF) families associated with stress responses differentially expressed in C. velia cultures under Hg stress. Our study presents the first in-depth transcriptomic analysis of C. velia, focusing on the expression of genes involved in different detoxification defense systems in response to heavy metal stress.
- MeSH
- Alveolata účinky léků genetika růst a vývoj metabolismus MeSH
- chemické látky znečišťující vodu toxicita MeSH
- chlorofyl metabolismus MeSH
- peroxid vodíku metabolismus MeSH
- reaktivní formy dusíku metabolismus MeSH
- reaktivní formy kyslíku metabolismus MeSH
- rtuť toxicita MeSH
- transkriptom účinky léků MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Chromera velia is a marine photosynthetic relative of human apicomplexan parasites. It has been isolated from coral reefs and is indicted for being involved in symbioses with hermatypic corals. C. velia has been subject to intensive research, but still very little is known of its response to light quality and quantity. Here, we have studied the growth and compositional responses of C. velia to culture under monochromatic light (blue, green or red), at two photon flux densities (PFD, 20 and 100 μmol photons m-2 s-1). Our results show that C. velia growth rate is unaffected by the quality of light, whereas it responds to PFD. However, light quality influenced cell size, which was smaller for cells exposed to blue monochromatic light, regardless of PFD. PFD strongly influenced carbon allocation: at 20 μmol photons m-2 s-1, carbon was mainly allocated into proteins while at 100 μmol photons m-2 s-1, carbon was allocated mainly into carbohydrate and lipid pools. The blue light treatment caused a decrease in the lipids and carbohydrates to proteins and thus suggested to affect nitrogen metabolism in acclimated cells. Whole-cell absorption spectra revealed the existence of red-shifted chlorophyll a antenna not only under red light but in all low PFD treatments. These findings show the ability of C. velia to successfully adapt and thrive in spectrally very different environments of coral reefs.
Endosymbioses necessitate functional cooperation of cellular compartments to avoid pathway redundancy and streamline the control of biological processes. To gain insight into the metabolic compartmentation in chromerids, phototrophic relatives to apicomplexan parasites, we prepared a reference set of proteins probably localized to mitochondria, cytosol, and the plastid, taking advantage of available genomic and transcriptomic data. Training of prediction algorithms with the reference set now allows a genome-wide analysis of protein localization in Chromera velia and Vitrella brassicaformis. We confirm that the chromerid plastids house enzymatic pathways needed for their maintenance and photosynthetic activity, but for carbon and nitrogen allocation, metabolite exchange is necessary with the cytosol and mitochondria. This indeed suggests that the regulatory mechanisms operate in the cytosol to control carbon metabolism based on the availability of both light and nutrients. We discuss that this arrangement is largely shared with apicomplexans and dinoflagellates, possibly stemming from a common ancestral metabolic architecture, and supports the mixotrophy of the chromerid algae.
- MeSH
- algoritmy MeSH
- Alveolata metabolismus MeSH
- cytosol metabolismus MeSH
- dusík metabolismus MeSH
- fotosyntéza genetika fyziologie MeSH
- fylogeneze MeSH
- molekulární evoluce MeSH
- symbióza genetika fyziologie MeSH
- uhlík metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Chromera velia is an alveolate alga which represents the closest known phototrophic relative to apicomplexan parasites. Although the nuclear, mitochondrial, and plastid genomes of this alga have been sequenced, the number of chromosomes and ploidy of C. velia are unknown. We explored ploidy in the vegetative cell, the predominant stage in cultures of Chromera, using the tyramide signal amplification-fluorescence in situ hybridization (TSA-FISH) in isolated nuclei of C. velia. Probes were derived from three single copy genes coding for 4-diphosphocytidyl-2-C-methyl-D-erythritol (CDP-ME) kinase, 2-C-methyl-D-erythritol 2,4-cyclodiphosphate (MEcPP) synthase and Topoisomerase II. Our results indicate that the vegetative cell of C. velia is haploid, as each probe produced a single fluorescent signal, although the possibility of diploidy with somatic pairing of homologous chromosomes cannot be completely excluded. Restriction analysis and hybridization with the telomere probe produced eight bands suggesting the presence of four chromosomes in haploid vegetative cells of C. velia. However, when the chromerid-specific telomere probe (TTTAGGG)4 was used for TSA-FISH, we consistently obtained a double signal. This may indicate that the four chromosomes are organized in clusters in interphase nuclei of C. velia, which is a chromosome organization similar to that of their apicomplexan relatives.
In the present work, we report the first comparative spectroscopic investigation between Photosystem I (PSI) complexes isolated from two red clade algae. Excitation energy transfer was measured in PSI from Chromera velia, an alga possessing a split PsaA protein, and from the model diatom Phaeodactylum tricornutum. In both cases, the estimated effective photochemical trapping time was in the 15-25ps range, i.e. twice as fast as higher plants. In contrast to green phototrophs, the trapping time was rather constant across the whole emission spectrum. The weak wavelength dependence was attributed to the limited presence of long-wavelength emitting chlorophylls, as verified by low temperature spectroscopy. As the trapping kinetics of C. velia PSI were barely distinguishable from those of P. tricornutum PSI, it was concluded that the scission of PsaA protein had no significant impact on the overall PSI functionality. In conclusion, the two red clade algae analysed here, carried amongst the most efficient charge separation so far reported for isolated Photosystems.
- MeSH
- Alveolata metabolismus MeSH
- chlorofyl metabolismus MeSH
- fluorescenční spektrometrie MeSH
- fotosystém I - proteinový komplex metabolismus MeSH
- kinetika MeSH
- přenos energie fyziologie MeSH
- Rhodophyta metabolismus MeSH
- rozsivky metabolismus MeSH
- světlosběrné proteinové komplexy metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Resonance Raman spectroscopy was used to evaluate pigment structure in the FCP-like light-harvesting complex of Chromera velia (Chromera light-harvesting complex or CLH). This antenna protein contains chlorophyll a, violaxanthin and a new isofucoxanthin-like carotenoid (called Ifx-l). We show that Ifx-l is present in two non-equivalent binding pockets with different conformations, having their (0,0) absorption maxima at 515 and 548nm respectively. In this complex, only one violaxanthin population absorbing at 486nm is observed. All the CLH-bound carotenoid molecules are in all-trans configuration, and among the two Ifx-l carotenoid molecules, the red one is twisted, as is the red-absorbing lutein in LHCII trimers. Analysis of the carbonyl stretching region for Chl a excitations indicates CLH binds up to seven Chl a molecules in five non-equivalent binding sites, in reasonable agreement with sequence analyses which have identified eight potential coordinating residues. The binding modes and conformations of CLH-bound pigments are discussed with respect to the known structures of LHCII and FCP.
Non-photochemical quenching (NPQ) is a photoprotective mechanism in light-harvesting antennae. NPQ is triggered by chloroplast thylakoid lumen acidification and is accompanied by violaxanthin de-epoxidation to zeaxanthin, which further stimulates NPQ. In the present study, we show that violaxanthin can act in the opposite direction to zeaxanthin because an increase in the concentration of violaxanthin reduced NPQ in the light-harvesting antennae of Chromera velia. The correlation overlapped with a similar relationship between violaxanthin and NPQ as observed in isolated higher plant light-harvesting complex II. The data suggest that violaxanthin in C. velia can act as an inhibitor of NPQ, indicating that violaxanthin has to be removed from the vicinity of the protein to reach maximal NPQ.
Four respiratory complexes and ATP-synthase represent central functional units in mitochondria. In some mitochondria and derived anaerobic organelles, a few or all of these respiratory complexes have been lost during evolution. We show that the respiratory chain of Chromera velia, a phototrophic relative of parasitic apicomplexans, lacks complexes I and III, making it a uniquely reduced aerobic mitochondrion. In Chromera, putative lactate:cytochrome c oxidoreductases are predicted to transfer electrons from lactate to cytochrome c, rendering complex III unnecessary. The mitochondrial genome of Chromera has the smallest known protein-coding capacity of all mitochondria, encoding just cox1 and cox3 on heterogeneous linear molecules. In contrast, another photosynthetic relative of apicomplexans, Vitrella brassicaformis, retains the same set of genes as apicomplexans and dinoflagellates (cox1, cox3, and cob).
- MeSH
- Alveolata genetika metabolismus MeSH
- Apicomplexa genetika MeSH
- cytochromy c metabolismus MeSH
- fotosyntéza genetika MeSH
- fylogeneze * MeSH
- genetická variace * MeSH
- genom mitochondriální MeSH
- kyselina mléčná metabolismus MeSH
- mitochondriální protonové ATPasy genetika metabolismus MeSH
- mitochondrie genetika metabolismus MeSH
- molekulární evoluce * MeSH
- paraziti genetika metabolismus MeSH
- respirační komplex I genetika metabolismus MeSH
- transport elektronů MeSH
- zvířata MeSH
- Check Tag
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
We report on energy transfer pathways in the main light-harvesting complex of photosynthetic relative of apicomplexan parasites, Chromera velia. This complex, denoted CLH, belongs to the family of FCP proteins and contains chlorophyll (Chl) a, violaxanthin, and the so far unidentified carbonyl carotenoid related to isofucoxanthin. The overall carotenoid-to-Chl-a energy transfer exhibits efficiency over 90% which is the largest among the FCP-like proteins studied so far. Three spectroscopically different isofucoxanthin-like molecules were identified in CLH, each having slightly different energy transfer efficiency that increases from isofucoxanthin-like molecules absorbing in the blue part of the spectrum to those absorbing in the reddest part of spectrum. Part of the energy transfer from carotenoids proceeds via the ultrafast S2 channel of both the violaxanthin and isofucoxanthin-like carotenoid, but major energy transfer pathway proceeds via the S1/ICT state of the isofucoxanthin-like carotenoid. Two S1/ICT-mediated channels characterized by time constants of ~0.5 and ~4ps were found. For the isofucoxanthin-like carotenoid excited at 480nm the slower channel dominates, while those excited at 540nm employs predominantly the fast 0.5ps channel. Comparing these data with the excited-state properties of the isofucoxanthin-like carotenoid in solution we conclude that, contrary to other members of the FCP family employing carbonyl carotenoids, CLH complex suppresses the charge transfer character of the S1/ICT state of the isofucoxanthin-like carotenoid to achieve the high carotenoid-to-Chl-a energy transfer efficiency.
The structure and composition of the light harvesting complexes from the unicellular alga Chromera velia were studied by means of optical spectroscopy, biochemical and electron microscopy methods. Two different types of antennae systems were identified. One exhibited a molecular weight (18-19kDa) similar to FCP (fucoxanthin chlorophyll protein) complexes from diatoms, however, single particle analysis and circular dichroism spectroscopy indicated similarity of this structure to the recently characterized XLH antenna of xanthophytes. In light of these data we denote this antenna complex CLH, for "Chromera Light Harvesting" complex. The other system was identified as the photosystem I with bound Light Harvesting Complexes (PSI-LHCr) related to the red algae LHCI antennae. The result of this study is the finding that C. velia, when grown in natural light conditions, possesses light harvesting antennae typically found in two different, evolutionary distant, groups of photosynthetic organisms.
