Associated group leaders are employed by other departments, but in their research projects they strongly interact with research groups at UPSC and take benefit from the UPSC scientific environment and infrastructure.
Plants need to integrate an array of signals to regulate complex patterns of gene expression. This is important since plants have specialized needs to respond to changes in the environment. Regulation of gene expression in plants is important for integration of external signals such as temperature, day length, concentration of different metabolites and light quality in the series of events that ultimately lead to flowering. Finally, the regulation of gene expression during specific stages of seed development is an interesting example of tissue and developmental control which is of considerable agricultural importance.
In all eukaryotes, protein-encoding genes are transcribed by RNA polymerase II (pol II). To perform its most basal functions; promoter recognition, melting of the DNA template at the transcription start, formation of the first phosphodiester bonds and promoter escape, pol II requires five so called general transcription factors (GTFs). These GTFs; TBP, TFIIB, E, F, and H are conserved in all eukaryotes and together with pol II they form a preinitiation complex comprising nearly 30 polypeptides. Mediator is a multisubunit complex which functions as a connector between the promoter-bound transcriptional regulators and pol II.
Surprisingly, Mediator had not been identified in plants until we recently succeeded to purify Mediator from A. thaliana through conventional biochemical purification combined with reversed-phase LC-ESI-MS/MS. This was the first description of Mediator in a plant, and it was evident that it required a biochemical approach since most of the A. thaliana Mediator subunits show very low sequence homol- ogy to the corresponding proteins in yeast and metazoans. Plant Mediator is probably structurally conserved, but the amino acid sequences of individual subunits differ considerably when compared to other eukaryotes. Plants also contain a set of unique Mediator subunits, which are likely to be involved in regulation of plant-specific gene expression.
Key publicationsBalciunas, D., Hallberg, M., Björklund, S., and Ronne, H. (2003) Functional interactions within yeast mediator and evi- dence of differential subunit modifications.J. Biol. Chem. 278:3831-3839.
Hallberg, M., Polozkov, G.V., Hu, G.Z., Beve, J., Gustafsson, C.M., Ronne, H., and Björklund, S. (2005) Site-specific Srb10- dependent phosphorylation of the yeast mediator subunit Med2 regulates gene expression from the 2-microm plas- mid. Proc. Natl. Acad. Sci. U. S. A. 101:3370-3375 (2004)
Björklund S., and Gustafsson C.M. The yeast mediator complex and its regulation. Trends. Biochem. Sci. 30:240- 244.
Hallberg, M., Hu, G-Z., Balciunas, D., Sheikhibrahim, Z., Björklund, S., and Ronne, H. (2006) Functional and physical inter- actions of the Mediator subunit Med21/Srb7. Mol. Genet Genomics 276:197-210
Bäckström, S., Elfving, N., Nilsson, R., Wingsle, G., and Björklund, S. (2007) Purification of a Plant Mediator from Arabi- dopsis thaliana identifies PFT1 as the Med25 subunit. Mo- lecular Cell 5: 717-729.
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The absorption of sunlight is the first step in the process of photosynthesis and is performed by a special group of proteins, called antenna proteins. Ligation of chlorophyll to the pigmentbinding proteins is a central step in the assembly of the photosynthetic apparatus. This process is complicated by the facts that i) free chlorophyll has a potentially damaging photooxidative activity in the light and ii) the pigmentbinding proteins are stabilized by chlorophyll, but in the absence of this pigment they are rapidly degraded. Therefore this process has to be highly coordinated, possibly by the use of special pigmentcarrier proteins.
Functional photosynthetic complexes only have a short lifespan, as a means of quality control. Turnover of pigmentbinding proteins and changes in the composition of lightharvesting and/or reaction centre pigmentprotein complexes are also the major tools for light adaptation. When the protein is degraded, pigments become free and may damage the cell. Under these conditions, pigmentcarrier proteins are extremely important. A special scenario for protein degradation is leaf senescence, which starts with a decrease in photosynthesis.
Carrier proteins – no matter if they function during assembly of new antenna proteins or during turnover of proteins - should be able to bind pigments transiently; uptake as well as handing over the chlorophylls must also be easy. Photooxidative damage by chlorophyll has to be prevented, either by quenchers like carotenoids or a special protein structure. Therefore, carrier proteins will not have the same features as normal antenna proteins. However, the hypothetical pigmentcarrier proteins known today have high structural homology to the antenna proteins. Despite this similarity, their regulation is very different.
Three model organisms are being studied: the tree Populus trichocarpa, the annual plant Arabidopsis thaliana and the cyanobacterium Synechocystis sp. PCC 6803. Using these organisms, interesting and relevant comparative studies are possible.
Key PublicationsStorm P, Hernandez-Prieto MA, Eggink LL, Hoober JK, Funk C (2008) The small CAB-like proteins of Synechocystis sp. PCC 6803 are able to bind pigments. Photosynth. Res., in press.
Yao D, Kieselbach T, Komenda J, Promnares K, Hernandez-Prieto M, Tichy M, Vermaas W, Funk C (2007) Localization of the small CAB-like proteins in the photosynthetic complexes, J. Biol. Chem. 282, 267-276.
Garcia-Lorenzo M, Sjödin A, Jansson S, Funk C (2006) Protease gene families in Populus and Arabidopsis, BMC Plant Biology 6:30.
Zelisko A, Garcia-Lorenzo M, Jackowsky G, Jansson S, Funk C (2005) AtFtsH6 is involved in the degradation of the light-harvesting complex II during high light acclimation and senescence. Proc. Natl. Acad. Sci. USA 102, 13699-13704.
Xu H, Vavilin D, Funk C, Vermaas W (2004) Multiple de- letions of small Cab-like proteins in the cyanobacterium Synechocystis sp.PCC 6803: consequences for pigment biosynthesis and accumulation. J. Biol. Chem. 279, 27971-27979.
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Wood is derived from stem cells that occur as a cylindrical sheet in the trunk of a tree. We investigate how genes regulate these stem cells. We are investigating this process in tree systems and in the more amenable species Arabidopsis. We have shown that cytokinin phytohormones are important regulators underlying cambial development.
In Arabidopsis we have identified two genes (CRE1/WOL, encoding a cytokinin receptor, and ; AHP6, encoding a regulator of cytokinin signalling), which has allowed us to show that cytokinins promote stem cell identity and inhibit the default xylem identity during root development. Decrease in cytokinin activity causes all vascular cells to differentiate into protoxylem cells. AHP6, an inhibitory protein, counteracts cytokinin signalling in a spatially specific manner, thereby allowing protoxylem formation. We have also shown that the CRE1/WOL cytokinin receptor is a bifunctional kinase/ phosphatase, and elimination of the negatively regulating phosphatase activity of CRE1/WOL results in stimulation of proliferation of vascular cell files. This indicates that in addition to specifying vascular cell identity, cytokinins have a further role in controlling the rate of proliferation of vascular cell files. We have also identified the first component (APL) of the regulatory machinery that defines whether the cell takes the wood or phloem vascular tissue fate.
An obvious step was to assess how much the Arabidopsis genetic information applies to economically important plants. In collaboration with Rishi Bhalerao and Karin Ljung we reduced cytokinin levels endogenously by engineering transgenic poplar trees (P. tremula x tremuloides) to express a cytokinin catabolic gene, Arabidopsis CYTOKININ OXIDASE 2. Transgenic trees showed reduced concentrations of a biologically active cytokinin, correlating with impaired cytokinin responsiveness. In these trees, radial growth and cambial activity were specifically compromised. Together, our results show that cytokinins are major hormonal regulators required for cambial development.
Key publicationsBonke M, Thitamadee S, Mähönen AP, Hauser MT, Helari- utta Y (2003) APL regulates vascular identity in Arabidop- sis. Nature 426: 181-186.
Mähönen AP, Bishopp A, Higuchi M, Nieminen KM, Ki- noshita K, Törmäkangas K, Ikeda Y, Oka A, Kakimoto T, Helariutta Y (2006) Cytokinin signaling and its inhibitor AHP6 regulate cell fate during vascular development. Sci- ence 311:94-98.
Mähönen AP, Higuchi M, Törmäkangas K, Kinosita K, Pischke M, Sussman MR, Helariutta Y, Kakimoto T (2006) Cytokinins regulated bidirectional phosphorelay network. Current Biology 16:1116-1122.
Tuskan GA et al. (2006) The genome of black cottonwood, Populus trichocarpa (Torr. & Gray). Science 313:1596-604.
Nieminen K, Immanen J, Laxell M, Kauppinen L, Tar- kowski P, Dolezal K, Tähtiharju S, Elo A, Decourteix M, Ljung K, Bhalerao R, Keinonen K, Albert VA, Helariutta Y (2008). Cytokinin signaling regulates cambial development in poplar. Procedings Natl Acad Sci USA:105:20032-20037.
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My research group is focused on understanding how plants are adapted to the environment in which they occur. We are interested in determining the actual genes involved in conferring local adaptation and how genetic variation in these genes has been shaped by evolutionary processes, such as natural selection and genetic drift.
The genetic basis of local adaptation
Natural selection can lead to genetic differentiation between populations for adaptive traits, even in the presence of substantial migration. A classic example in forest trees is adaptation to the steep latitudinal gradient in the length of growing season that characterizes northern environments. Trees often show latitudinal clines in traits, such as the timing of bud set, the onset of flowering and frost hardening. We are investigating the genetic basis of phenological traits that are responsible for climatic adaptations in European aspen (Populus tremula). We are using a collection of P. tremula genotypes (the SwAsp collection) to infer the genetic basis of phenology traits along a latitudinal gradient across Sweden. We are using a combination of association mapping techniques and molecular population genetic studies to link variation in candidate genes to naturally occurring variation in phenology.
The genetic basis of plant defence
Plants have evolved numerous adaptations to defend themselves against attack by herbivores and my group is also studying the genetic basis of plant resistance using the SwAsp collection. We are currently inferring historical patterns of evolution of genes involved in herbivore defence using molecular population genetic methods and using association mapping to dissect naturally occurring variation in herbivore resistance in the SwAsp collection. Many important phenotypic adaptations are mediated by changes in gene regulation, rather than through changes in protein coding sequences, and we are also investigating genes involved in signal transduction pathways that induce wound responses in P. tremula.
Key publicationsIngvarsson, PK (2002) A metapopulation perspective on genetic diversity and differentiation in partially self-fertilizing plants. Evolution 56; 2368-2373
Ingvarsson, PK (2005) Nucleotide polymorphism and linkage disequilibrium within and among natural populations of European aspen (Populus tremula L., Salicaceae). Genetics 169: 945-953
Ingvarsson, PK (2007) Gene expression and protein length influence codon usage and rates of sequence evolution in Populus tremula. Molecular Biology and Evolution, 24: 836-844
Ingvarsson, PK, Garcia, MV, Luquez, V, Hall, D and Jansson, S (2008) Nucleotide polymorphism and phenotypic associations within and around the phytochromeB2 locus in European aspen (Populus tremula, Salicaceae). Genetics 178: 2217-2226
Ingvarsson, PK (2008) Multilocus patterns of nucleotide polymorphism and the demographic history of Populus tremula. Genetics 180: 329-340
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Our research focuses on the modelling of physical systems, in particular charge transport, collective, and nonlinear effects. Such models have a wide range of applicability, and the knowledge obtained from one physical system can often be applied to a completely different system, due to similarities in the mathematical structures of the models. Thus, the strength of our research lies in generality, and in this respect we may learn things from, e.g. ocean waves, that are applicable to optical fibres or to the quantum transport of charges in nanoscale devices.
We have paid particular attention to problems concerning so-called plasma systems, i.e. electrically conducting gases, in which the collective nature of the plasma constituents gives rise to long-range phenomena, instead of close-range collisional interactions. Instead of being just a game of billiards, the charges move and create electric and magnetic fields that further interact with particles at large distances. Such interactions are extremely important in many applications, ranging from semiconductors to welding flames. As many fundamental properties rely on charge transport, understanding the dynamics of such plasmas can be an important tool for treating a diverse set of systems.
Many important processes in biological systems are governed by charge transport phenomena, photosynthesis being no exception. In particular, we have chosen to study the problem of proton transport in PSII, of fundamental importance for the understanding of photosynthesis. Here we are developing new self-consistent models for proton transfer and we are further implementing these codes in numerical schemes in order to make comparisons with experiments.
Key publicationsM. Marklund and P. K. Shukla (2006) Nonlinear collective effects in photon-photon and photon-plasma interactions, Reviews of Modern Physics 78, 591-640
M. Marklund and G. Brodin (2007) Dynamics of spin-1/2 quantum plasmas, Physical Review Letters 98, 025001
Dan Anderson, Björn Hall, Mietek Lisak, and Mattias Marklund (2002) Statistical effects in the multistream model for quantum plasmas, Physical Review E 65, 046417
M. Marklund (2005) Classical and quantum kinetics of the Zakharov system, Physics of Plasmas 12, 082110
Lundström, E.; Brodin, G.; Lundin, J.; Marklund, M.; Bingham, R.; Collier, J.; Mendonça, J. T.; Norreys, P. (2001) Proposal for Detection of QED Vacuum Nonlinearities in Maxwell's Equations by the Use of Waveguides, Physical Re- view Letters 96, 083602
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Photosystem II (PSII) is a unique, specialized protein complex that uses light energy to oxidize water, resulting in the release of molecular oxygen into the atmosphere. PSII performs this reaction within a functional unit known as the water-oxidizing complex (WOC) or the oxygen-evolving complex (OEC). The WOC consists of an inorganic manganese-oxygen-calcium core (Mn4OxCa complex) surrounded by a functionally important ligand sphere. Understanding the structure of the WOC and its water-splitting mechanism is not only of academic interest, but is also important for the development of artificial water-splitting catalysts, for which the WOC often serves as a blueprint.
Although crystal structures are available for PSII, the detailed structure of the WOC cannot be discerned from them, because of specific radiation damage to the Mn4OxCa cluster. We are therefore trying to derive the structure of the water- splitting complex of photosystem II by a combination of biophysical techniques, such as magnetic resonance (EPR, NMR), X-ray spectroscopy, time-resolved mass spectrometry, electrochemistry and quantum mechanical calculations. These experiments are performed within a network of local and international collaborations. Special emphasis is given to the question of how substrate water is coordinated to the Mn4OxCa cluster. Comparative studies on Mn model complexes and genetically modified photosystem II complexes are carried out to guide data interpretation.
In a new second line of experiments, artificial water-splitting and hydrogen-producing catalysts are being studied under various experimental conditions with an electrochemical cell that is directly coupled to a membrane-inlet mass spectrometer. These activity studies will help our understanding of the water-splitting mechanisms and capacities of such artificial catalysts, which is crucial for their improvement. The ultimate goal is the construction of an ‘artificial leaf’ that uses sunlight to split water into O2 and H2
Key publicationsMessinger J, Badger M, Wydrzynski T (1995) Detection of one slowly exchanging substrate water molecule in the S3 state of photosystem II. Proc. Natl. Acad. Sci. USA 92: 3209- 3213
Messinger J, Nugent JH, Evans MCW (1997) Detection of an EPR multiline signal for the S0* state in photosystem II. Biochemistry 36: 11055-11060
Yano J, Kern J, Sauer KH, Latimer M, Pushkar Y, Biesiadka J, Loll B, Saenger W, Messinger J, Zouni A, Yachandra VK (2006) Where water is oxidized to dioxygen: Structure of the Mn4Ca cluster in photosystem II. Science 314: 821-825
Kulik, LV, Epel B, Lubitz W, Messinger J (2007) Electronic structure of the Mn4OxCa cluster in the S0 and S2 states of the oxygen-evolving complex of photosystem II based on pulse 55Mn-ENDOR and EPR spectroscopy. J. Am. Chem. Soc. 129: 13421-13435
Lubitz W, Reijerse EJ, Messinger J (2008) Solar water- splitting into H2 and O2: design principles of photosystem II and hydrogenases. Energy Environ. Sci. 1: 15-31
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We use and develop chemometrics tools and strategies for global phenotyping of transgenic and wild type Poplar trees. Chemometrics represents a key philosophy and technology, since it is used for planning experiments to maximise information, to obtain good predictions and to visualize collected complex data. We apply a systems biology approach, in which multiple profiling techniques, e.g. metabolomics and proteomics, are combined to elucidate biochemical mechanisms and pathways at different organization levels.
Experimental sciences, e.g. biology, chemistry and medicine, have to a large extent become information sciences and, in turn, bioinformatics and chemometrics are now prerequisites for experimental and applied research. Our aim is to develop and apply a systems biology approach to study growth and development in Poplar (the tree model) and Arabidopsis (the universal plant model) - all this in collaboration with Umeå Plant Science Centre and the Computational Life Science Cluster at Umeå University. We have already developed and optimized experimental protocols and data modelling tools to enable global phenotyping of thousands of plants using low-, semi- and high-throughput molecular profiling techniques for both Poplar and Arabidopsis. We have also developed novel strategies for generating and combining transcriptomic, proteomic and metabolomic profile data acquired from parallel analyses of hybrid aspen (Populus tremula × P. tremuloides). However, further research is needed to develop systems informatics tools and existing databases and statistical modeling to ‘catch up’ with the challenges that new experimental technologies provide.
Computational Life Science cluster (CLiC)
In our multidisciplinary approach, we integrate the fields of biology, mathematics, chemistry, physics and informatics. As a result, we have established a unique bioinformatics cluster, the Computational Life Science cluster (CLiC) at the Chemical Biology Centre (KBC), which encompass more than 30 researchers working together from six different departments. CLiC will stimulate and advance our already world-leading experimental research in forest biotechnology, by providing the missing link in informatics and modelling.
Key publicationsTrygg, J. and S. Wold, Orthogonal projections to latent structures (O-PLS), Journal of Chemometrics, 2002 16(3), p:119-128.
Trygg J, Holmes E, Lundstedt T, Chemometrics in metabonomics. J. Proteome Res 6 (2): 469-479, 2007
Bylesjö, M., D. Eriksson, M. Kusano, T. Moritz and J. Trygg, Data integration in plant biology: the O2PLS method for combined modeling of transcript and metabolite data, Plant Journal, 2007 52(6), p:1181-1191.
Bylesjö M, Nilsson R, Srivastava V, Grönlund A, Johansson, AI, Jansson S, Karlsson J, Moritz T, Wingsle G, Trygg J, Integrated Analysis of Transcript, Protein and Metabolite Data to Study Lignin Biosynthesis in Hybrid Aspen, J. Proteome Res. 2009, 8, 199-210
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Hybridization among plants may lead to the formation of new species and adaptation to novel habitats. We investigate the genetic and ecological mechanisms involved in diploid hybrid speciation in pines.
Hybridization is an important force in plant evolution. It can quickly create evolutionary novelties that promote adaptation and speciation. Pinus densata forms extensive forests on the Tibetan Plateau. Documented evidence indicates that P. densata originated via natural hybridization between two other pine species, and dates back to the uplift of the plateau 5-10 million years ago. Its ancient history and unique adaptation offer a rare opportunity to study the genetic basis of speciation. Natural populations of the ancient hybrid, populations at the species’ boundaries and man-made F1 hybrids will be used in comparative analyses. By combining genetic and ecological approaches with molecular functional studies, we are investigating the tempo and mode of the hybrid speciation. This project is relevant to understanding the patterns of functional divergence of gene families and the relationship between genetic variation and ecological diversification. This project is being run in close collaboration with the Institute of Botany, Chinese Academy of Sciences.
Marker-based pedigree reconstruction
Pedigree reconstruction is a key to investigating several major issues in genetics and breeding. Accurate pedigree construction and parentage assignment require high-resolution DNA markers and advanced statistical methods. In this project, we explore the possibility to reconstruct sibship structures from wind-pollinated progenies of Scots pine and Norway spruce seed orchards. This research is relevant to evaluating the gene diversity and gain of seed orchard crops, which supply more than 50% of the seedlings used in Swedish forest plantations, and the feasibility of low-input breeding programs in the future. This project is being run in collaboration with the Forest Genetics section (SLU) of UPSC.
Key PublicationsWang, X.-R., Szmidt, A.E. & Savolainen, O. 2001. Genetic composition and diploid hybrid speciation of a high moun- tain pine, Pinus densata, native to the Tibetan plateau. Genetics 159: 337-346.
Song, B.-H., Wang, X.-Q., Wang, X.-R., Ding, K.-Y. & Hong, D.-Y. 2003. Cytoplasmic composition in Pinus densa- ta and population establishment of the diploid hybrid pine. Molecular Ecology 12:2995-3001.
Zeng, Q.-Y. & Wang, X.-R. 2005. Catalytic properties of glutathione-binding residues in a τ class glutathione transferase (PtGSTU1) from Pinus tabulaeformis. FEBS Letters 579: 2657–2662.
Ma, X.-F., Szmidt, A.E. & Wang, X.-R. 2006. Genetic structure and evolutionary history of a diploid hybrid pine Pinus densata inferred from the nucleotide variation at seven gene loci. Molecular Biology and Evolution. 23:807-816.
Mao, J.-F., Li, Y. & Wang, X.-R. 2008. Empirical assessment of the reproductive fitness components of the hybrid pine Pinus densata on the Tibetan Plateau. Evolutionay Ecology, DOI 10.1007/s10682-008-9244-6.
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Understanding of protein folding processes, and how external factors such as metals affect these reactions, is critical for finding treatments of many debilitating human conditions (e.g., Alzheimer’s, Parkinson’s, prion and Wilson’s diseases). Knowledge about protein folding is also crucial for applications in protein design and structure predictions. The projects in my lab focus on fundamental aspects of folding reactions, using model systems as well as specific human proteins involved in key metabolic pathways. Some of our research aims to increase mechanistic knowledge of how proteins fold in vitro and in vivo.
The major focus of this part of the work is on two key classes of proteins: cofactor-binding proteins and oligomeric proteins. Folding of these proteins involves not only polypeptide folding, but also inter-protein interactions and the folding pathways may be greatly affected by cofactor interactions and protein-protein interactions, respectively. Projects focus on, for example, azurin (copper), flavodoxin (flavin), myoglobin (heme), and co-chaperonin proteins (heptamers). To mimic the crowded cellular environment, experiments are performed in the presence of crowding agents. We recently discovered that crowding has dramatic effects on both the folding and native-state shape of a Borrelia protein. The other branch of my research aims to understand the proteins involved in cellular copper transport. In human cells, the copper chaperone Atox1 delivers copper to Wilson and Menke’s proteins in the Golgi network, which then load the metal onto targets, such as the ferroxidase, ceruloplasmin. Projects within this remit concern folding, interaction and transfer properties of involved proteins from different species. For all projects, a range of equilibrium and kinetic biophysical (often spectroscopic) and biochemical techniques are combined with strategic protein mutagenesis and theoretical approaches to characterize the selected systems. Together with Prof. Samuelsson, I am probing the biophysical behaviour of the chloroplast protein PsbO in cell-like conditions.
Key publicationsCrowded, cell-like environment induces shape changes in aspherical protein M Perham, D Homouz, A Samiotakis, M Cheung, P Wittung-Stafshede, Proc Nat Acad Sci USA, 2008, 105, 11754-11759.
Molecular crowding enhances native structure and stability of α/β protein flavodoxin L Stagg, S-Q Zhang, M Cheung, P Wittung-Stafshede Proc Nat Acad Sci USA 2007,104, 18976-18981
Stability of the nucleotide-binding subdomain of the Wilson disease protein: Role of the common H1069Q mutation in ATP coordination A Rodriguez-Granillo, E Sedlak, P Wittung-Stafshede J Mol Biol, 2008, 383, 1097-111.
Conserved residues modulate copper release in human copper chaperone Atox1 F Hussain, JS Olson, P Wittung-Stafshede, Proc. Nat. Acad. Sci. 2008, 105, 11158-11163.
Discrete roles of copper ions in chemical unfolding of human ceruloplasmin E Sedlak, P Wittung-Stafshede, Biochemistry, 2007, 46(33):9638-44.
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The photosystem II (PSII) complex, responsible for splitting water and releasing oxygen, is located mainly in the grana thylakoid membrane. The complex consists of more than 30 different protein subunits, and has a molecular mass of more than 700 kDa. Eighteen of the subunits are low molecular mass proteins (< 10 kDa), all of which contain a single transmembrane span and their protein sequences are highly conserved among photosynthetic organisms. Why are so many single-transmembrane spanning protein subunits found in the PSII complex?
The light driven photosynthetic electron transport of green plants is mediated by chlorophyll-binding protein complexes located in the thylakoid membrane within the chloroplast. The thylakoid membrane has a complex structure, with lateral segregation of protein complexes into distinct regions referred to as the grana and stroma lamellae. The components involved in the light reactions are organized in five supracomplexes: Photosystem I (PSI) and II (PSII), light harvesting complex (LHCII), ATP-synthase and the cytochrome b6/f complex. For these entire complexes, we have medium to high resolution structural information, even though the location of several of the low molecular mass proteins still are unclear. Recently, it has become known that these complexes interact and form higher orders of association complexes, like mega-organized super-complexes within the membrane.
It has been assumed, suggested and accepted that various protein complexes can migrate between the two thylakoid regions. For instance, the antenna protein complex LHCII has been shown to migrate out of the grana region upon phosphorylation. Also, turnover and assembly of the grana-located Photosystem II complex may need migration. On the other hand, the grana thylakoids are among the most protein-dense membranes found in living cells, with suggested 70-80% protein contents. Thus, the mechanism of protein diffusion in such a densely packed membrane is difficult to understand. The protein complexes in the thylakoid membrane must be organized in a manner that optimises migration and allows fast diffusion. How is this achieved? We think that a set of low molecular mass proteins are involved in this process.
So far, isolation of various knock-out mutants of the small proteins has not given clear indications of the functions for several of them. However, recently we have obtained new data that have given us a breakthrough. The data clearly show that the characteristic phosphorylation pattern of the PSII reaction centre proteins is dramatically changed upon deletion of two small proteins. Furthermore, the structure of the thylakoid membrane was found to be changed, so that no PSII-LHCII super complex could be detected.
Key publicationsLundberg E, Storm P, Schröder WP, Funk C (2011) Crystal structure of the TL29 protein from Arabidopsis thaliana: An APX homolog without peroxidase activity.
J Struct Biol. 176(1):24-31
Shi L, Hall M, Funk C, Schröder WP (2012) Photosystem II, a growing complex: Updates on newly discovered components and low molecular mass proteins.
Biochimica et Biophysica Acta – Bioenergetics. 1817 (2012), pp. 13-25
Garcia-Cerdán JG, Kovács L, Tóth T, Kereiche S, Avseeva E, Boekema EJ, Mamedov F, Funk C, Schröder WP (2011) The PsbW protein stabilizes the supramolecular organization of photosystem II in higher plants.
The Plant Journal. 65: 368-381
Hall M, Mata-Cabana A, Åkerlund H-E, Florencio FJ, Schröder WP, Lindahl M, Kieselbach T (2010) Thioredoxin targets of the plant chloroplast lumen and their implications for plastid function.
García-Cerdán JG, Sveshnikov D, Dewez D, Jansson S, Funk C, and Schröder WP. (2008) Antisense inhibition of the PsbX protein Affects PSII integrity in higher plant Arabidopsis thaliana. Plant Cell Physiol 50:1-12
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