In photosynthetic electron transport, large multiprotein complexes are connected by small diffusible electron carriers, the mobility of which is challenged by macromolecular crowding. For thylakoid membranes of higher plants, a long-standing question has been which of the two mobile electron carriers, plastoquinone or plastocyanin, mediates electron transport from stacked grana thylakoids where photosystem II (PSII) is localized to distant unstacked regions of the thylakoids that harbor PSI. Here, we confirm that plastocyanin is the long-range electron carrier by employing mutants with different grana diameters. Furthermore, our results explain why higher plants have a narrow range of grana diameters since a larger diffusion distance for plastocyanin would jeopardize the efficiency of electron transport. In the light of recent findings that the lumen of thylakoids, which forms the diffusion space of plastocyanin, undergoes dynamic swelling/shrinkage, this study demonstrates that plastocyanin diffusion is a crucial regulatory element of plant photosynthetic electron transport.
- MeSH
- biologické modely MeSH
- fotosystém I - proteinový komplex metabolismus MeSH
- fotosystém II - proteinový komplex metabolismus MeSH
- Magnoliopsida fyziologie MeSH
- plastocyanin metabolismus MeSH
- počítačová simulace MeSH
- regulace genové exprese u rostlin fyziologie MeSH
- transport elektronů MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Research Support, U.S. Gov't, Non-P.H.S. MeSH
Survival of phototrophic organisms depends on their ability to collect and convert enough light energy to support their metabolism. Phototrophs can extend their absorption cross section by using diverse pigments and by tuning the properties of these pigments via pigment-pigment and pigment-protein interaction. It is well known that some cyanobacteria can grow in heavily shaded habitats by utilizing far-red light harvested with far-red-absorbing chlorophylls d and f. We describe a red-shifted light-harvesting system based on chlorophyll a from a freshwater eustigmatophyte alga Trachydiscus minutus (Eustigmatophyceae, Goniochloridales). A comprehensive characterization of the photosynthetic apparatus of T. minutus is presented. We show that thylakoid membranes of T. minutus contain light-harvesting complexes of several sizes differing in the relative amount of far-red chlorophyll a forms absorbing around 700 nm. The pigment arrangement of the major red-shifted light-harvesting complex is similar to that of the red-shifted antenna of a marine alveolate alga Chromera velia. Evolutionary aspects of the algal far-red light-harvesting complexes are discussed. The presence of these antennas in eustigmatophyte algae opens up new ways to modify organisms of this promising group for effective use of far-red light in mass cultures.
- MeSH
- biologické pigmenty metabolismus MeSH
- diuron MeSH
- fluorescenční spektrometrie MeSH
- Heterokontophyta metabolismus účinky záření MeSH
- membránové proteiny metabolismus MeSH
- sladká voda * MeSH
- světlo * MeSH
- světlosběrné proteinové komplexy metabolismus MeSH
- teplota MeSH
- tylakoidy metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
Photosystem I (PSI) is a multi-subunit integral pigment-protein complex that performs light-driven electron transfer from plastocyanin to ferredoxin in the thylakoid membrane of oxygenic photoautotrophs. In order to achieve the optimal photosynthetic performance under ambient irradiance, the absorption cross section of PSI is extended by means of peripheral antenna complexes. In eukaryotes, this role is played mostly by the pigment-protein complexes of the LHC family. The structure of the PSI-antenna supercomplexes has been relatively well understood in organisms harboring the primary plastid: red algae, green algae and plants. The secondary endosymbiotic algae, despite their major ecological importance, have so far received less attention. Here we report a detailed structural analysis of the antenna-PSI association in the stramenopile alga Nannochloropsis oceanica (Eustigmatophyceae). Several types of PSI-antenna assemblies are identified allowing for identification of antenna docking sites on the PSI core. Instances of departure of the stramenopile system from the red algal model of PSI-Lhcr structure are recorded, and evolutionary implications of these observations are discussed.
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
Diatoms greatly contribute to carbon fixation and thus strongly influence the global biogeochemical balance. Capable of chromatic acclimation (CA) to unfavourable light conditions, diatoms often dominate benthic ecosystems in addition to their planktonic lifestyle. Although CA has been studied at the molecular level, our understanding of this phenomenon remains incomplete. Here we provide new data to better explain the acclimation-associated changes under red-enhanced ambient light (RL) in diatom Phaeodactylum tricornutum, known to express a red-shifted antenna complex (F710). The complex was found to be an oligomer of a single polypeptide, Lhcf15. The steady-state spectroscopic properties of the oligomer were also studied. The oligomeric assembly of the Lhcf15 subunits is required for the complex to exhibit a red-shifted absorption. The presence of the red antenna in RL culture coincides with the development of a rounded phenotype of the diatom cell. A model summarizing the modulation of the photosynthetic apparatus during the acclimation response to light of different spectral quality is proposed. Our study suggests that toggling between alternative organizations of photosynthetic apparatus and distinct cell morphologies underlies the remarkable acclimation capacity of diatoms.
- MeSH
- fenotyp * MeSH
- fyziologická adaptace MeSH
- multimerizace proteinu MeSH
- rozsivky fyziologie účinky záření MeSH
- spektrální analýza MeSH
- světlosběrné proteinové komplexy metabolismus MeSH
- vodní organismy fyziologie účinky záření MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Spatial segregation of photosystems in the thylakoid membrane (lateral heterogeneity) observed in plants and in the green algae is usually considered to be absent in photoautotrophs possessing secondary plastids, such as diatoms. Contrary to this assumption, here we show that thylakoid membranes in the chloroplast of a marine diatom, Phaeodactylum tricornutum, contain large areas occupied exclusively by a supercomplex of photosystem I (PSI) and its associated Lhcr antenna. These membrane areas, hundreds of nanometers in size, comprise hundreds of tightly packed PSI-antenna complexes while lacking other components of the photosynthetic electron transport chain. Analyses of the spatial distribution of the PSI-Lhcr complexes have indicated elliptical particles, each 14 × 17 nm in diameter. On larger scales, the red-enhanced illumination exerts a significant effect on the ultrastructure of chloroplasts, creating superstacks of tens of thylakoid membranes.
- MeSH
- chloroplasty metabolismus účinky záření ultrastruktura MeSH
- fotosystém I - proteinový komplex metabolismus MeSH
- fotosystém II - proteinový komplex metabolismus MeSH
- multiproteinové komplexy metabolismus ultrastruktura MeSH
- rozsivky metabolismus účinky záření ultrastruktura MeSH
- světlo MeSH
- světlosběrné proteinové komplexy metabolismus MeSH
- transmisní elektronová mikroskopie MeSH
- tylakoidy metabolismus účinky záření ultrastruktura MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
We present proteomic, spectroscopic, and phylogenetic analysis of light-harvesting protein (Lhc) function in oleaginous Nannochloropsis oceanica (Eustigmatophyta, Stramenopila). N. oceanica utilizes Lhcs of multiple classes: Lhcr-type proteins (related to red algae LHCI), Lhcv (VCP) proteins (violaxanthin-containing Lhcs related to Lhcf/FCP proteins of diatoms), Lhcx proteins (related to Lhcx/LhcSR of diatoms and green algae), and Lhc proteins related to Red-CLH of Chromera velia. Altogether, 17 Lhc-type proteins of the 21 known from genomic data were found in our proteomic analyses. Besides Lhcr-type antennas, a RedCAP protein and a member of the Lhcx protein subfamily were found in association with Photosystem I. The free antenna fraction is formed by trimers of a mixture of Lhcs of varied origins (Lhcv, Lhcr, Lhcx, and relatives of Red-CLH). Despite possessing several proteins of the Red-CLH-type Lhc clade, N. oceanica is not capable of chromatic adaptation under the same conditions as the diatom Phaeodactylum tricornutum or C. velia. In addition, a naming scheme of Nannochloropsis Lhcs is proposed to facilitate further work.
The remarkable adaptability of diatoms living in a highly variable environment assures their prominence among marine primary producers. The present study integrates biochemical, biophysical and genomic data to bring new insights into the molecular mechanism of chromatic adaptation of pennate diatoms in model species Phaeodactylum tricornutum, a marine eukaryote alga possessing the capability to shift its absorption up to ~700 nm as a consequence of incident light enhanced in the red component. Presence of these low energy spectral forms of Chl a is manifested by room temperature fluorescence emission maximum at 710 nm (F710). Here we report a successful isolation of the supramolecular protein complex emitting F710 and identify a member of the Fucoxanthin Chlorophyll a/c binding Protein family, Lhcf15, as its key building block. This red-shifted antenna complex of P. tricornutum appears to be functionally connected to photosystem II. Phylogenetic analyses do not support relation of Lhcf15 of P. tricornutum to other known red-shifted antenna proteins thus indicating a case of convergent evolutionary adaptation towards survival in shaded environments.
- MeSH
- barva * MeSH
- chlorofyl metabolismus MeSH
- fluorescence * MeSH
- fluorescenční spektrometrie MeSH
- fotosystém II - proteinový komplex metabolismus MeSH
- fylogeneze MeSH
- fyziologická adaptace * MeSH
- hmotnostní spektrometrie s elektrosprejovou ionizací MeSH
- rozsivky fyziologie MeSH
- světlo MeSH
- světlosběrné proteinové komplexy metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
A novel chlorophyll a containing pigment-protein complex expressed by cells of Chromera velia adapted to growth under red/far-red illumination [1]. Purification of the complex was achieved by means of anion-exchange chromatography and gel-filtration. The antenna is shown to be an aggregate of ~20kDa proteins of the light-harvesting complex (LHC) family, unstable in the isolated form. The complex possesses an absorption maximum at 705nm at room temperature in addition to the main chlorophyll a maximum at 677nm producing the major emission band at 714nm at room temperature. The far-red absorption is shown to be the property of the isolated aggregate in the intact form and lost upon dissociation. The purified complex was further characterized by circular dichroism spectroscopy and fluorescence spectroscopy. This work thus identified the third different class of antenna complex in C. velia after the recently described FCP-like and LHCr-like antennas. Possible candidates for red antennas are identified in other taxonomic groups, such as eustigmatophytes and the relevance of the present results to other known examples of red-shifted antenna from other organisms is discussed. This work appears to be the first successful isolation of a chlorophyll a-based far-red antenna complex absorbing above 700nm unrelated to LHCI.
- MeSH
- aniontoměniče MeSH
- Apicomplexa metabolismus MeSH
- chlorofyl metabolismus MeSH
- chromatografie iontoměničová MeSH
- cirkulární dichroismus MeSH
- fluorescenční spektrometrie metody MeSH
- gelová chromatografie MeSH
- spektrofotometrie ultrafialová metody MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
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.
