Nejvíce citovaný článek - PubMed ID 29464563
Organization of Plant Photosystem II and Photosystem I Supercomplexes
The heart of oxygenic photosynthesis is the water-splitting photosystem II (PSII), which forms supercomplexes with a variable amount of peripheral trimeric light-harvesting complexes (LHCII). Our knowledge of the structure of green plant PSII supercomplex is based on findings obtained from several representatives of green algae and flowering plants; however, data from a non-flowering plant are currently missing. Here we report a cryo-electron microscopy structure of PSII supercomplex from spruce, a representative of non-flowering land plants, at 2.8 Å resolution. Compared with flowering plants, PSII supercomplex in spruce contains an additional Ycf12 subunit, Lhcb4 protein is replaced by Lhcb8, and trimeric LHCII is present as a homotrimer of Lhcb1. Unexpectedly, we have found α-tocopherol (α-Toc)/α-tocopherolquinone (α-TQ) at the boundary between the LHCII trimer and the inner antenna CP43. The molecule of α-Toc/α-TQ is located close to chlorophyll a614 of one of the Lhcb1 proteins and its chromanol/quinone head is exposed to the thylakoid lumen. The position of α-Toc in PSII supercomplex makes it an ideal candidate for the sensor of excessive light, as α-Toc can be oxidized to α-TQ by high-light-induced singlet oxygen at low lumenal pH. The molecule of α-TQ appears to shift slightly into the PSII supercomplex, which could trigger important structure-functional modifications in PSII supercomplex. Inspection of the previously reported cryo-electron microscopy maps of PSII supercomplexes indicates that α-Toc/α-TQ can be present at the same site also in PSII supercomplexes from flowering plants, but its identification in the previous studies has been hindered by insufficient resolution.
- MeSH
- alfa-tokoferol * analýza metabolismus MeSH
- elektronová kryomikroskopie MeSH
- fotosyntéza MeSH
- fotosystém II - proteinový komplex * metabolismus MeSH
- rostliny metabolismus MeSH
- tylakoidy metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Názvy látek
- alfa-tokoferol * MeSH
- fotosystém II - proteinový komplex * MeSH
The acclimation of higher plants to different light intensities is associated with a reorganization of the photosynthetic apparatus. These modifications, namely, changes in the amount of peripheral antenna (LHCII) of photosystem (PS) II and changes in PSII/PSI stoichiometry, typically lead to an altered chlorophyll (Chl) a/b ratio. However, our previous studies show that in spruce, this ratio is not affected by changes in growth light intensity. The evolutionary loss of PSII antenna proteins LHCB3 and LHCB6 in the Pinaceae family is another indication that the light acclimation strategy in spruce could be different. Here we show that, unlike Arabidopsis, spruce does not modify its PSII/PSI ratio and PSII antenna size to maximize its photosynthetic performance during light acclimation. Its large PSII antenna consists of many weakly bound LHCIIs, which form effective quenching centers, even at relatively low light. This, together with sensitive photosynthetic control on the level of cytochrome b6f complex (protecting PSI), is the crucial photoprotective mechanism in spruce. High-light acclimation of spruce involves the disruption of PSII macro-organization, reduction of the amount of both PSII and PSI core complexes, synthesis of stress proteins that bind released Chls, and formation of "locked-in" quenching centers from uncoupled LHCIIs. Such response has been previously observed in the evergreen angiosperm Monstera deliciosa exposed to high light. We suggest that, in contrast to annuals, shade-tolerant evergreen land plants have their own strategy to cope with light intensity changes and the hallmark of this strategy is a stable Chl a/b ratio.
- Klíčová slova
- Arabidopsis thaliana, LHCII antenna, Light acclimation, Non-photochemical quenching, Photoprotection, Photosynthetic control, Picea abies, Thylakoid membrane,
- MeSH
- aklimatizace MeSH
- Arabidopsis * metabolismus MeSH
- chlorofyl a metabolismus MeSH
- chlorofyl metabolismus MeSH
- cytochromy b metabolismus MeSH
- fotosystém I - proteinový komplex metabolismus MeSH
- fotosystém II - proteinový komplex metabolismus MeSH
- komplex cytochromů b6f metabolismus MeSH
- proteiny tepelného šoku metabolismus MeSH
- smrk * metabolismus MeSH
- světlo MeSH
- světlosběrné proteinové komplexy metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
- Názvy látek
- chlorofyl a MeSH
- chlorofyl MeSH
- cytochromy b MeSH
- fotosystém I - proteinový komplex MeSH
- fotosystém II - proteinový komplex MeSH
- komplex cytochromů b6f MeSH
- proteiny tepelného šoku MeSH
- světlosběrné proteinové komplexy MeSH
Photosynthetic light-harvesting antennae are pigment-binding proteins that perform one of the most fundamental tasks on Earth, capturing light and transferring energy that enables life in our biosphere. Adaptation to different light environments led to the evolution of an astonishing diversity of light-harvesting systems. At the same time, several strategies have been developed to optimize the light energy input into photosynthetic membranes in response to fluctuating conditions. The basic feature of these prompt responses is the dynamic nature of antenna complexes, whose function readily adapts to the light available. High-resolution microscopy and spectroscopic studies on membrane dynamics demonstrate the crosstalk between antennae and other thylakoid membrane components. With the increased understanding of light-harvesting mechanisms and their regulation, efforts are focusing on the development of sustainable processes for effective conversion of sunlight into functional bio-products. The major challenge in this approach lies in the application of fundamental discoveries in light-harvesting systems for the improvement of plant or algal photosynthesis. Here, we underline some of the latest fundamental discoveries on the molecular mechanisms and regulation of light harvesting that can potentially be exploited for the optimization of photosynthesis.
The largest stable photosystem II (PSII) supercomplex in land plants (C2S2M2) consists of a core complex dimer (C2), two strongly (S2) and two moderately (M2) bound light-harvesting protein (LHCB) trimers attached to C2 via monomeric antenna proteins LHCB4-6. Recently, we have shown that LHCB3 and LHCB6, presumably essential for land plants, are missing in Norway spruce (Picea abies), which results in a unique structure of its C2S2M2 supercomplex. Here, we performed structure-function characterization of PSII supercomplexes in Arabidopsis (Arabidopsis thaliana) mutants lhcb3, lhcb6, and lhcb3 lhcb6 to examine the possibility of the formation of the "spruce-type" PSII supercomplex in angiosperms. Unlike in spruce, in Arabidopsis both LHCB3 and LHCB6 are necessary for stable binding of the M trimer to PSII core. The "spruce-type" PSII supercomplex was observed with low abundance only in the lhcb3 plants and its formation did not require the presence of LHCB4.3, the only LHCB4-type protein in spruce. Electron microscopy analysis of grana membranes revealed that the majority of PSII in lhcb6 and namely in lhcb3 lhcb6 mutants were arranged into C2S2 semi-crystalline arrays, some of which appeared to structurally restrict plastoquinone diffusion. Mutants without LHCB6 were characterized by fast induction of non-photochemical quenching and, on the contrary to the previous lhcb6 study, by only transient slowdown of electron transport between PSII and PSI. We hypothesize that these functional changes, associated with the arrangement of PSII into C2S2 arrays in thylakoids, may be important for the photoprotection of both PSI and PSII upon abrupt high-light exposure.
- MeSH
- Arabidopsis genetika metabolismus MeSH
- fotosystém II - proteinový komplex genetika metabolismus MeSH
- proteiny huseníčku genetika metabolismus MeSH
- proteiny vázající chlorofyl genetika metabolismus MeSH
- smrk metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Názvy látek
- fotosystém II - proteinový komplex MeSH
- Lhcb6 protein, Arabidopsis MeSH Prohlížeč
- proteiny huseníčku MeSH
- proteiny vázající chlorofyl MeSH
Diatoms are a large group of marine algae that are responsible for about one-quarter of global carbon fixation. Light-harvesting complexes of diatoms are formed by the fucoxanthin chlorophyll a/c proteins and their overall organization around core complexes of photosystems (PSs) I and II is unique in the plant kingdom. Using cryo-electron tomography, we have elucidated the structural organization of PSII and PSI supercomplexes and their spatial segregation in the thylakoid membrane of the model diatom species Thalassiosira pseudonana. 3D sub-volume averaging revealed that the PSII supercomplex of T. pseudonana incorporates a trimeric form of light-harvesting antenna, which differs from the tetrameric antenna observed previously in another diatom, Chaetoceros gracilis. Surprisingly, the organization of the PSI supercomplex is conserved in both diatom species. These results strongly suggest that different diatom classes have various architectures of PSII as an adaptation strategy, whilst a convergent evolution occurred concerning PSI and the overall plastid structure.
- MeSH
- fotosyntéza * MeSH
- fotosystém I - proteinový komplex ultrastruktura MeSH
- fotosystém II - proteinový komplex ultrastruktura MeSH
- rozsivky metabolismus ultrastruktura MeSH
- tylakoidy ultrastruktura MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Názvy látek
- fotosystém I - proteinový komplex MeSH
- fotosystém II - proteinový komplex MeSH
Photosystem II (PSII) complexes are organized into large supercomplexes with variable amounts of light-harvesting proteins (Lhcb). A typical PSII supercomplex in plants is formed by four trimers of Lhcb proteins (LHCII trimers), which are bound to the PSII core dimer via monomeric antenna proteins. However, the architecture of PSII supercomplexes in Norway spruce[Picea abies (L.) Karst.] is different, most likely due to a lack of two Lhcb proteins, Lhcb6 and Lhcb3. Interestingly, the spruce PSII supercomplex shares similar structural features with its counterpart in the green alga Chlamydomonas reinhardtii [Kouřil et al. (2016) New Phytol. 210, 808-814]. Here we present a single-particle electron microscopy study of isolated PSII supercomplexes from Norway spruce that revealed binding of a variable amount of LHCII trimers to the PSII core dimer at positions that have never been observed in any other plant species so far. The largest spruce PSII supercomplex, which was found to bind eight LHCII trimers, is even larger than the current largest known PSII supercomplex from C. reinhardtii. We have also shown that the spruce PSII supercomplexes can form various types of PSII megacomplexes, which were also identified in intact grana membranes. Some of these large PSII supercomplexes and megacomplexes were identified also in Pinus sylvestris, another representative of the Pinaceae family. The structural variability and complexity of LHCII organization in Pinaceae seems to be related to the absence of Lhcb6 and Lhcb3 in this family, and may be beneficial for the optimization of light-harvesting under varying environmental conditions.
- Klíčová slova
- Picea abies, Pinus sylvestris, clear native polyacrylamide electrophoresis, grana membrane, megacomplex, photosystem II, single-particle electron microscopy, supercomplex,
- MeSH
- fotosystém II - proteinový komplex chemie metabolismus MeSH
- smrk metabolismus MeSH
- světlosběrné proteinové komplexy chemie metabolismus MeSH
- terciární struktura proteinů MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Názvy látek
- fotosystém II - proteinový komplex MeSH
- světlosběrné proteinové komplexy MeSH
