Chromerids are a group of alveolates, found in corals, that show peculiar morphological and genomic features. These organisms are evolutionary placed in-between symbiotic dinoflagellates and parasitic apicomplexans. There are two known species of chromerids: Chromera velia and Vitrella brassicaformis. Here, the biochemical composition of the C. velia cell wall was analyzed. Several polysaccharides adorn this structure, with glucose being the most abundant monosaccharide (approx. 80%) and predominantly 4-linked (approx. 60%), suggesting that the chromerids cell wall is mostly cellulosic. The presence of cellulose was cytochemically confirmed with calcofluor white staining of the algal cell. The remaining wall polysaccharides, assuming structures are similar to those of higher plants, are indicative of a mixture of galactans, xyloglucans, heteroxylans, and heteromannans. The present work provides, for the first time, insights into the outermost layers of the photosynthetic alveolate C. velia.

• Klíčová slova
• Chromera velia, Alveolata, calcofluor white, cell wall, cellulose, chromerids, monosaccharide linkage analysis,
• MeSH
• Alveolata * MeSH
• buněčná stěna MeSH
• fotosyntéza MeSH
• fylogeneze MeSH
• polysacharidy MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• polysacharidy MeSH

Heme biosynthesis is essential for almost all living organisms. Despite its conserved function, the pathway's enzymes can be located in a remarkable diversity of cellular compartments in different organisms. This location does not always reflect their evolutionary origins, as might be expected from the history of their acquisition through endosymbiosis. Instead, the final subcellular localization of the enzyme reflects multiple factors, including evolutionary origin, demand for the product, availability of the substrate, and mechanism of pathway regulation. The biosynthesis of heme in the apicomonad Chromera velia follows a chimeric pathway combining heme elements from the ancient algal symbiont and the host. Computational analyses using different algorithms predict complex targeting patterns, placing enzymes in the mitochondrion, plastid, endoplasmic reticulum, or the cytoplasm. We employed heterologous reporter gene expression in the apicomplexan parasite Toxoplasma gondii and the diatom Phaeodactylum tricornutum to experimentally test these predictions. 5-aminolevulinate synthase was located in the mitochondria in both transfection systems. In T. gondii, the two 5-aminolevulinate dehydratases were located in the cytosol, uroporphyrinogen synthase in the mitochondrion, and the two ferrochelatases in the plastid. In P. tricornutum, all remaining enzymes, from ALA-dehydratase to ferrochelatase, were placed either in the endoplasmic reticulum or in the periplastidial space.

• Klíčová slova
• Chromera velia, heterologous expression, predictions, tetrapyrrole biosynthesis,
• MeSH
• Alveolata fyziologie   MeSH
• Apicomplexa metabolismus   MeSH
• biologický transport MeSH
• hem metabolismus   MeSH
• metabolické sítě a dráhy * MeSH
• mitochondrie genetika   metabolismus   ultrastruktura   MeSH
• molekulární evoluce MeSH
• protozoální proteiny chemie   genetika   metabolismus   MeSH
• regulace genové exprese enzymů MeSH
• rozsivky metabolismus   MeSH
• sekvence aminokyselin MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• hem MeSH
• protozoální proteiny MeSH

Aminoacyl-tRNA synthetases (AaRSs) are enzymes that catalyze the ligation of tRNAs to amino acids. There are AaRSs specific for each amino acid in the cell. Each cellular compartment in which translation takes place (the cytosol, mitochondria, and plastids in most cases), needs the full set of AaRSs; however, individual AaRSs can function in multiple compartments due to dual (or even multiple) targeting of nuclear-encoded proteins to various destinations in the cell. We searched the genomes of the chromerids, Chromera velia and Vitrella brassicaformis, for AaRS genes: 48 genes encoding AaRSs were identified in C. velia, while only 39 AaRS genes were found in V. brassicaformis. In the latter alga, ArgRS and GluRS were each encoded by a single gene occurring in a single copy; only PheRS was found in three genes, while the remaining AaRSs were encoded by two genes. In contrast, there were nine cases for which C. velia contained three genes of a given AaRS (45% of the AaRSs), all of them representing duplicated genes, except AsnRS and PheRS, which are more likely pseudoparalogs (acquired via horizontal or endosymbiotic gene transfer). Targeting predictions indicated that AaRSs are not (or not exclusively), in most cases, used in the cellular compartment from which their gene originates. The molecular phylogenies of the AaRSs are variable between the specific types, and similar between the two investigated chromerids. While genes with eukaryotic origin are more frequently retained, there is no clear pattern of orthologous pairs between C. velia and V. brassicaformis.

• Klíčová slova
• Aminoacyl tRNA synthetase (AaRS), Chromera velia, Vitrella brassicaformis, chloroplast, evolution, mitochondrion, nucleus, protein localization,
• MeSH
• Alveolata klasifikace   enzymologie   genetika   MeSH
• aminoacyl-tRNA-synthetasy genetika   MeSH
• fylogeneze MeSH
• protozoální proteiny genetika   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• aminoacyl-tRNA-synthetasy MeSH
• protozoální proteiny MeSH

Photoprotective non-photochemical quenching (NPQ) represents an effective way to dissipate the light energy absorbed in excess by most phototrophs. It is often claimed that NPQ formation/relaxation kinetics are determined by xanthophyll composition. We, however, found that, for the alveolate alga Chromera velia, this is not the case. In the present paper, we investigated the reasons for the constitutive high rate of quenching displayed by the alga by comparing its light harvesting strategies with those of a model phototroph, the land plant Spinacia oleracea. Experimental results and in silico studies support the idea that fast quenching is due not to xanthophylls, but to intrinsic properties of the Chromera light harvesting complex (CLH) protein, related to amino acid composition and protein folding. The pKa for CLH quenching was shifted by 0.5 units to a higher pH compared with higher plant antennas (light harvesting complex II; LHCII). We conclude that, whilst higher plant LHCIIs are better suited for light harvesting, CLHs are 'natural quenchers' ready to switch into a dissipative state. We propose that organisms with antenna proteins intrinsically more sensitive to protons, such as C. velia, carry a relatively high concentration of violaxanthin to improve their light harvesting. In contrast, higher plants need less violaxanthin per chlorophyll because LHCII proteins are more efficient light harvesters and instead require co-factors such as zeaxanthin and PsbS to accelerate and enhance quenching.

• MeSH
• Alveolata fyziologie   MeSH
• bílkoviny řas metabolismus   MeSH
• fotosyntéza * MeSH
• protony * MeSH
• protozoální proteiny metabolismus   MeSH
• rostlinné proteiny metabolismus   MeSH
• Spinacia oleracea fyziologie   MeSH
• světlosběrné proteinové komplexy metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• srovnávací studie MeSH
• Názvy látek
• bílkoviny řas MeSH
• protony * MeSH
• protozoální proteiny MeSH
• rostlinné proteiny MeSH
• světlosběrné proteinové komplexy MeSH