Structure and dynamics of the thylakoid membrane

• Professor James Barber FRS, Imperial College London, UK

Biography

Professor James Barber, born 16 July 1940, is the Ernst Chain Professor of Biochemistry at the Imperial College London, Visiting Nanyang Professor to Nanyang Technological University, Singapore and Visiting Professor to the Politecnico di Torino, Italy. He is Fellow of the Royal Society, Fellow of the Royal Society of Chemistry, a member of the European Academy (Academia Europæa) and a foreign member of the Royal Swedish Academy of Sciences. Recently, he served as President of the International Society of Photosynthesis Research.

Professor Barber graduated from the University of Wales with a degree in Chemistry, and later gained a MSc and PhD in Biophysics from the University of East Anglia. After a postdoctoral year in The Netherlands, he joined the academic staff at Imperial College London as a Lecturer in 1968. He was promoted to Full Professor in 1979.  In 1988, he served as Dean of the Royal College of Science, and from 1989 to 1999 was Head of the Biochemistry Department at Imperial College. Professor Barber has been awarded   honorary doctorates from Stockholm University and the University of East Anglia.

Professor Barber was awarded the Flintoff Medal by the Royal Society of Chemistry in 2002, the Italgas/Eni Prize for Energy and Enivronment in 2005, the Biochemical Society Novartis medal and prize in 2006, and the Wheland Medal and Prize from the University of Chicago in 2007.  In 2008 he gave Daniel Arnon Lecture,University of California, Berkeley, in 2009 Kuan Yew Distinguished Visitors Lectures (Singapore) and the G8University Summit Energy Lecture (Torino, Italy). Very recently he gave the Sir Ernst Chain Distinguished Lecture, Imperial College London.

Professor Barber primarily works on the molecular processes of Photosynthesis. The focus of his research has been the investigation of photosynthesis and the functional role of the photosystems with emphasis on their structures. Much of his work has focused on Photosystem Two, a biological machine able to use light energy to split water into oxygen and reducing equivalents, and Professor Barber contributed greatly to this subject by elucidating the structure of the catalytic centre for this reaction. To date, he has published over 500 research and review articles and produced 16 books covering various aspects of photosynthesis research.

• Professor Peter Horton FRS, Sheffield University, UK

Biography

Professor Peter Horton is Emeritus Professor of Biochemistry in the Department of Molecular Biology and Biotechnology at the University of Sheffield. He holds a DPhil and DSc from the University of York and received postdoctoral training at Purdue University. He was appointed as Assistant Professor at the State University of New York at Buffalo in 1975, took up the post of Lecturer in Biochemistry at the University of Sheffield in 1978, was promoted to Reader in 1984 and to Professor in 1990. He was elected Fellow of the Royal Society in 2010. His research has concerned the regulation of the light reactions of photosynthesis, particularly the transformations that enable the photosynthetic apparatus to deal efficiently with limiting light and to dissipate excess light during environmental stress. He contributed to establishing the role of LHCII phosphorylation in the state transitions, developing the methodology and framework of chlorophyll fluorescence analysis and determining the mechanisms underlying photoprotective energy dissipation or nonphotochemical quenching. He has also studied how light harvesting regulation is related to the ecophysiology of plant species, and how it may play a part in limiting photosynthesis and abiotic stress tolerance in crop plants.

• Professor James Barber FRS, Imperial College London, UK
• Audio recording (mp3)

Biography

Professor James Barber, born 16 July 1940, is the Ernst Chain Professor of Biochemistry at the Imperial College London, Visiting Nanyang Professor to Nanyang Technological University, Singapore and Visiting Professor to the Politecnico di Torino, Italy. He is Fellow of the Royal Society, Fellow of the Royal Society of Chemistry, a member of the European Academy (Academia Europæa) and a foreign member of the Royal Swedish Academy of Sciences. Recently, he served as President of the International Society of Photosynthesis Research.

Professor Barber graduated from the University of Wales with a degree in Chemistry, and later gained a MSc and PhD in Biophysics from the University of East Anglia. After a postdoctoral year in The Netherlands, he joined the academic staff at Imperial College London as a Lecturer in 1968. He was promoted to Full Professor in 1979.  In 1988, he served as Dean of the Royal College of Science, and from 1989 to 1999 was Head of the Biochemistry Department at Imperial College. Professor Barber has been awarded   honorary doctorates from Stockholm University and the University of East Anglia.

Professor Barber was awarded the Flintoff Medal by the Royal Society of Chemistry in 2002, the Italgas/Eni Prize for Energy and Enivronment in 2005, the Biochemical Society Novartis medal and prize in 2006, and the Wheland Medal and Prize from the University of Chicago in 2007.  In 2008 he gave Daniel Arnon Lecture,University of California, Berkeley, in 2009 Kuan Yew Distinguished Visitors Lectures (Singapore) and the G8University Summit Energy Lecture (Torino, Italy). Very recently he gave the Sir Ernst Chain Distinguished Lecture, Imperial College London.

Professor Barber primarily works on the molecular processes of Photosynthesis. The focus of his research has been the investigation of photosynthesis and the functional role of the photosystems with emphasis on their structures. Much of his work has focused on Photosystem Two, a biological machine able to use light energy to split water into oxygen and reducing equivalents, and Professor Barber contributed greatly to this subject by elucidating the structure of the catalytic centre for this reaction. To date, he has published over 500 research and review articles and produced 16 books covering various aspects of photosynthesis research.

Abstract

It was the work of Jan Anderson, together with Keith Boardman (1) that showed it was possible to physically separate Photosystem I (PSI) from Photosysten II (PSII)  and later it was Jan Anderson (2) who realised the importance of this work in terms of the fluid-mosaic model as applied to the thylakoid membrane. Since then there has been a steady progress in the development of biochemical procedures to isolate both PSII and PSI for physical, biochemical, molecular biological and structural studies, culminating in their crystallization and structural determination at atomic resolution. There are crystal structures for PSII and PSI isolated from cyanobacteria (3,4,5,6) and for PSI   from higher plants (7). In the case of higher plants, the biochemical procedures developed have built on the recognition that PSII and PSI are lateral separated between granal and stromal regions as proposed by Jan Anderson and Bertil Andersson (8)

The structure of the cyanobacterial PSII has now been resolved to 1.9A (5). It is a dimer having a molecular mass of 700 kDa and the crystal structures have provided  organisational details of  the 19/20 subunits (16/17 intrinsic and 3 extrinsic) which make up each monomer and revealed information about the position and protein environments of  the cofactors involved in the absorption of light, charge separation and water splitting. This level of detail has yet to be elucidated for higher plant PSII especially important because there are a number of significant differences between  PSII of cyanobacteria and that of higher plants including differences in core subunits composition (both intrinsic and extrinsic) and light harvesting systems (Chla/Chlb binding proteins in plants and phycobilisomes in cyanobacteria). Progress towards this end will be presented.

References:
1.         Boardman, N K & Anderson, J M.  1964 Isolation from spinach chloroplasts of particles containing different proportions of chlorophyll a and chlorophyll b and their possible role in the light reactions of photosynthesis. Nature 203, 166-167.
2.         Anderson, J M.  1975 The molecular organization of chloroplast thylakoids. Biochim  Biophys  Acta 416, 191-235.
3.         Ferreira, K N, Iverson, T M, Maghlaoui, K, Barber J &  Iwata, S. 2004 Architecture of the photosynthetic oxygen evolving center. Science 303, 1831–1838.
4.         Loll, B, Kern, J, Saenger, W, Zouni, A & Biesiadka, J. 2005 Towards complete cofactor arrangement in the 3.0 Å resolution structure of photosystem II. Nature 438, 1040–1044.
5          Umena, Y, Kawakami, K, Shen, J R & Kamiya, N. 2011 Crystal structure of oxygen-evolving photosystem II at a resolution of 1.9 Å. Nature 473, 55–60.
6.         Jordan, P, Fromme, P, Witt, H T, Klukas, O, Saenger, W & Krauß, N. 2001 Three-dimensional structure of cyanobacterial photosystem I at 2.5 Å resolution. Nature 411, 909–917.
7.         Amunts, A, Drory, O & Nelson, N. 2007 The structure of a plant photosystem I supercomplex at 3.4 Å resolution. Nature 447, 58–63.
8.         Andersson, B & Anderson, J M. 1980 Lateral heterogeneity in the distribution of chlorophyll protein complexes of the thylakoid membranes of spinach chloroplasts. Biochim Biophys Acta 593, 427–440.

• Professor Nathan Nelson, Tel Aviv University, Israel
• Audio recording (mp3)

Biography

Biography not yet available.

Abstract

Abstract not yet available.

• Professor William Cramer, Purdue University, USA
• Audio recording (mp3)

Biography

Bill Cramer's career can be summarized as a step down by a factor of 10 to the exponent nineteen, the energy in electron-volts (eV) of the cosmic rays that he studied as an undergraduate and grad student, to the 1 eV characteristic energy of the electron transfer events that he studies in analysis of structure-function of the photosynthetic cytochrome b6f electron transport complex. As a consequence of attempts to follow these different trajectories of charged atomic particles, and studies on other problems in membrane protein structural biology, he is a Fellow of the Biophysical Society and Henry Koffler Distinguished Professor of Biological Sciences at Purdue University.

Abstract

Lipid binding sites and properties were compared in the hetero-oligomeric cytochrome b₆f and bc₁ complexes that function in photosynthetic and respiratory membrane energy transduction.  Seven lipid binding sites in the cyanobacterial b₆f complex overlap three natural sites in the Chlamydomonasreinhardtii algal complex and four sites in the yeast mitochondrial bc₁ complex.  Inferences of lipid binding sites and functions are supported by sequence, interatomic distance, and B-factor information on interacting lipid groups and coordinating amino acid residues. Lipid functions in the b₆f complex include the consequence of substitution of the eighth (‘H’) trans-membrane helix present in the mitochondrial cytochrome b subunit by a lipid and chlorin ring in b₆f. The question of the function of this lipid substitution is of interest. The quinol oxidation site is on the p- (lumenal) side of the ‘H’ helix or the substituted lipid. Oxidation of PQH₂ is coupled to the n (stromal)-side activation of an LHC kinase.  It is suggested that the presence of the lipid may enable the trans-membrane signaling that activates the kinase. (Support from NIH GM-038323). 

Co-authors:
S S Hasan, Purdue University, USA
E Yamashita, Osaka University, Japan

• Professor Sir John Walker FRS, University of Cambridge, UK
• Audio recording (mp3)

Biography

John Walker is Director of the Medical Research Council Mitochondrial Biology Unit in Cambridge, UK. From 1974-1998 at the Laboratory of Molecular Biology he established the details of the modified genetic code of mitochondria, helped to discover overlapping genes in bacteriophages and discovered two protein sequence motifs involved in binding nucleotides to which his name has become attached. They are the most widely dispersed motifs in the biological world. His work led in 1994 to the determination of the 3D structure of the catalytic domain of the ATP synthase, which pointed towards a mechanical rotary mechanism of coupling of transmembrane protonmotive force to ATP synthesis. Recently he has demonstrated that the energy cost of making an ATP molecule is constant throughout multi-cellular animals from man to sponges, but not in unicellular organisms.  He continues to work towards a complete understanding of this extraordinary machine.

In 1997, he was awarded the Nobel Prize in Chemistry jointly with Dr Paul Boyer for their elucidation of the enzymatic mechanism underlying the synthesis of adenosine triphosphate (ATP).

He is a Fellow of the Royal Society, a Fellow of the Academy of Medical Sciences, and a Foreign Associate of the US National Academy of Sciences.

Abstract

The ATP synthase found in chloroplasts has many features in common with the ATP synthases found in eubacteria and mitochondria. Their overall architectures are similar, and they all consist of two rotary motors linked by a stator and a flexible rotor. When rotation of the membrane bound rotor is driven by proton motive force, the direction of rotation ensures that ATP is made from ADP and phosphate in the globular catalytic domain. When ATP serves as the source of energy and is hydrolysed in the catalytic domain, the rotor turns in the opposite sense and protons are pumped outwards through the membrane domain, and away from the catalytic domain. The lecture will describe the common features of their catalytic mechanisms. However, the ATP synthase from chloroplasts, eubacteria and mitochondria differ in several key features, in their mechanisms of regulation and most fundamentally in the energy cost that is paid to make an ATP molecule. The most efficient ATP synthase is found in the mitochondria from multicellular animals. The ATP synthases in unicellular organisms, and chloroplasts, pay various higher costs that seem to reflect the supply of available energy.

• Professor Jan Anderson FRS, Australian National University, Australia
• Audio recording (mp3)

Biography

Professor Jan M Anderson was awarded her BSc in 1954 and MSc (Hons) 1^st Class in 1956 in Chemistry at the University of Otago, New Zealand. Following the Award of the only King George VI Scholarship for New Zealand, she went to the University of California (Berkeley) (1956-1959) gaining her PhD in 1959 with Professor Melvin Calvin as her Supervisor. In 1961, Jan came to Canberra to the CSIRO, Division of Plant Industry to do research on the light reaction of photosynthesis. She became a Fellow of the Australian Academy of Science in 1987 and a Fellow of the Royal Society in 1996. Her research interests include proof of the concept of two photosystems (PS); the molecular organization of plant thylakoid membranes; the significance of lateral heterogeneity of PSII and PSI between stacked and unstacked thylakoid membranes; sun/shade and light quality and quantity acclimation, and the significance of the grana stacking. She was an Original Thomson ISI Highly Cited Researcher in Plant Biology in 2002, and the ISI Australian Citation Laureate on Plant and Animal Sciences in 2004. 

Abstract

The concept that in photosynthesis two photosystems cooperate in series, immortalised in Hill and Bendall’s (1960) Z scheme, was still a black box defining neither structural nor the molecular organization of the photosystems within thylakoids. Digitonin  fragmentation of  isolated chloroplasts, followed by differential centrifugation, yielded a heavier granal fraction enriched in PSII which bound a third “enigmatic” cytochrome b-559, and a lighter PSI fraction, proving that indeed there were two photosystems.  The differentiation of the continuous thylakoid membrane network into grana and stroma thylakoids is a morphological reflection of the non-random distribution of PSII and PSI and ATP synthase, which became known as lateral heterogeneity. Long-term acclimation of sun versus shade plants modulates the composition and function and membrane appression of thylakoids. Significantly, highly dynamic rapid grana-stacking/ destacking, with reversible macro-organization of PSII/LHCII supercomplex arrays within grana optimise photosynthetic function in vivo over the entire range of irradiance; this still poses a grana conundrum.

Co-author:
Wah Soon Chow, Australian National University, Australia

• Professor Werner Kühlbrandt, Max-Planck-Institute of Biophysics, Germany
• Audio recording (mp3)

Biography

Werner Kühlbrandt studied chemistry and crystallography in Berlin, and went on to do his PhD with Nigel Unwin at the MRC Laboratory of Molecular Biology in Cambridge, UK, investigating the structure of two-dimensional ribosome crystals by electron microscopy. He turned to structural studies of membrane proteins as a postdoc, first at the ETH Zürich, and then at Imperial College London. After a brief interlude at UC Berkeley, CA, he became a group leader at the EMBL Heidelberg in 1988. Since 1997 he is a director at the Max Planck Institute of Biophysics in Frankfurt, Germany, where his department of Structural Biology studies the structure and mechanisms of membrane proteins by X-ray and electron crystallography, single-particle cryo-EM, electron tomography and biophysical techniques.

Abstract

Electron cryo-microscopy (cryo-EM) covers a larger size range than any other technique in structural biology, from atomic resolution structures of membrane proteins, to large non-crystalline single molecules, entire organelles or even cells.

Electron crystallography of two-dimensional (2D) crystals makes it possible to examine membrane proteins in the quasi-native environment of a lipid bilayer at high to moderately high resolution. Recently, we have used electron crystallography to investigate functionally important conformational changes in membrane transport proteins such as the sodium/proton antiporters NhaA and NhaP, or the structure of channelrhodopsin.

“Single particle” cryo-EM is well suited to study the structure of large macromolecular assemblies in the 3.2 to 20Å resolution range.  A recent example is our 19Å map of a mitochondrial respiratory chain supercomplex consisting of one copy of complex 1, two copies of complex III, and one of complex IV.  The fit of the x-ray structures to our map indicates short pathways for efficient electron shuttling between complex I and III by ubiquinol, and between complex III and IV by cytochrome c.

Electron cryo-tomography can visualize large protein complexes in their cellular context at 30-50Å resolution, bridging the gap between protein crystallography and light microscopy. Cryo-ET is particularly suitable for studying biological membranes and large membrane protein complexes in situ. Cryo-ET of chloroplast thylakoids revealed the ATP synthase in flat stromal membranes and grana end membranes. We also could localize photosystem-II dimers in stacked and unstacked grana membranes.  Together with the high-resolution structure of LHC-II, this enabled us to build a molecular model of membrane interaction in chloroplast grana. 

In mitochondria of 6 different species we studied (2 mammals, 3 fungi, 1 plant), we found long rows of ATP synthase dimers along the tightly curved cristae ridges, whereas it is always monomeric and confined to flat membrane regions in chloroplasts. The proton pumps of the mitochondrial respiratory chain seemed to be confined to the flat membrane regions on either side of the dimer rows. This highly conserved arrangement appears to be a fundamental feature of all mitochondria from healthy cells, and suggests a fundamental role of the mitochondrial cristae as proton traps for efficient ATP synthesis.  Interestingly, the inner membrane of mitochondria from the aging model organism Podospora anserina, a filamentous fungus with a fixed life span of ~20 days, undergoes a dramatic change as the cells age, and the dimer rows break up.

References:

Goswami P, Paulino C, Hizlan D, Vonck J, Yildiz Ö, Kühlbrandt W  (2010) Structure of the archaeal Na+/H+ antiporter NhaP1 and functional role of transmembrane helix 1. EMBO J. 30, 439-449.

Strauss M, Hofhaus G, Schröder R R, Kühlbrandt W (2008) Dimer ribbons of ATP synthase shape the inner mitochondrial membrane. EMBO J 27, 1154-1160.

Single-particle analysis:
Gipson P, Mills D, Wouts R, Grininger M, Vonck J, Kühlbrandt W (2010):
Direct structural insight into the substrate-shuttling mechanism of yeast fatty acid synthase by electron cryomicroscopy.
Proc Natl Acad Sci USA107, 9164-9169

Electron crystallography:
Kühlbrandt W, Wang DN, Fujiyoshi Y (1994):
Atomic model of plant light-harvesting complex by electron crystallography. Nature367, 614-621.      

Appel M, Hizlan D, Vinothkumar KR, Ziegler C and Kühlbrandt W (2009):
Conformations of NhaA, the Na⁺/H⁺ exchanger from Escherichia coli, in the pH-activated and ion-translocating states.
J Mol Biol388, 659-672.

Electron cryo-tomography:
Strauss M, Hofhaus G, Schröder RR, Kühlbrandt W (2008):
Dimer ribbons of ATP synthase shape the inner mitochondrial membrane.
EMBO J27, 1154-1160.

Daum B, Nicastro D, Austin II J, McIntosh JR, Kühlbrandt W (2010):
Arrangement of photosystem-II and ATP synthase in chloroplast membranes of spinach and pea.
Plant Cell22, 1299-1312. 

• Professor Egbert Boekema, Groningen University, The Netherlands
• Audio recording (mp3)

Biography

Egbert Boekema was born in Groningen in 1952, studied (bio) chemistry at the University of Groningen and completed a PhD degree on the structure of the mitochondrial membrane protein NADH: ubiquinone oxidoreductase (complex I) in 1984. Electron microscopy and membrane proteins have been his key interests since then. First as a post-doctoral fellow from 1984 – 1989 in the department of electron microscopy at the Fritz‑Haber‑Institute of the Max‑Planck‑Society in Berlin, where he became interested in photosynthesis by Jan Dekker and Matthias Rögner, and later back in Groningen with a fellowship of the Dutch Academy of Arts and Sciences. In 2004 he was appointed as professor and currently he is also serving as head of the GGB research school. His main topics are supercomplex structures from chloroplasts and mitochondria. He published on many relevant photosynthetic complexes, including photosystem I and II, IsiA, PsbS, ATPase, cytochrome b6f, phycobilisomes, chlorosomes, RC-Lh1, Lh2, LHCII and NDH-1. Last but not least he investigated   the structure of plant thylakoid membranes by cryo-electron tomography and single particle averaging. In his free time he likes bird watching in the countryside.

Abstract 

Electron microscopy and single particle averaging are important tools to investigate structures of large membrane proteins. For instance, supercomplexes of plant thylakoid membranes and inner mitochondrial membranes are a popular topic. In this contribution, we performed an investigation on isolated RC-LH1 complexes of Rhodobaca with the aim of establishing the peripheral antenna conformation, and in particular the structural role of PufX. Rhodobaca is an alkaliphilic purple nonsulfur bacterium found in African Rift valley soda lakes [Milford 2000]. Projection maps of dimeric complexes were obtained at 13 Å resolution and show the positions of the α-helices of 2x14 LH1 units subunits. They are organized in two half-rings of 2 x 13 units. In addition, there are two units in the interface of the two halves of the dimer. Between the interface and the two half rings are two openings on each side. Next to the openings there are additional densities present, considered to be occupied by in total 4 PufX molecules. The model differs from previously proposed configurations for other purple bacteria, in which the LH1 ribbon is continuous, but with two openings at the end and in which the dimeric RC-LH1 complex contains only two PufX molecules.

Reference:
Milford, A D, Achenbach, L A, Jung, D O and Madigan, M T (2000) Rhodobaca bogoriensis gen nov and sp nov, an alkaliphilic purple nonsulfur bacterium from African Rift Valley soda lakes. Arch Microbiol 174, 18-27

Co-authors:
Dmitry A Semchonok, University of Groningen, The Netherlands
Colette Jungas, CEA, DSV, IBEB, Laboratoire de Biologie Cellulaire and CNRS, UMR Biologie Végétale et Microbiologie Environnementales/Université Aix-Marseille,  France

• Professor Peter Horton FRS, Sheffield University, UK
• Audio recording (mp3)

Biography

Professor Peter Horton is Emeritus Professor of Biochemistry in the Department of Molecular Biology and Biotechnology at the University of Sheffield. He holds a DPhil and DSc from the University of York and received postdoctoral training at Purdue University. He was appointed as Assistant Professor at the State University of New York at Buffalo in 1975, took up the post of Lecturer in Biochemistry at the University of Sheffield in 1978, was promoted to Reader in 1984 and to Professor in 1990. He was elected Fellow of the Royal Society in 2010. His research has concerned the regulation of the light reactions of photosynthesis, particularly the transformations that enable the photosynthetic apparatus to deal efficiently with limiting light and to dissipate excess light during environmental stress. He contributed to establishing the role of LHCII phosphorylation in the state transitions, developing the methodology and framework of chlorophyll fluorescence analysis and determining the mechanisms underlying photoprotective energy dissipation or nonphotochemical quenching. He has also studied how light harvesting regulation is related to the ecophysiology of plant species, and how it may play a part in limiting photosynthesis and abiotic stress tolerance in crop plants.

Abstract

The distinctive lateral organisation of the protein complexes in the thylakoid membrane discovered by Jan Anderson and colleagues is dependent of the balance of various attractive and repulsive forces.  Modulation of these forces allows critical physiological regulation of photosynthesis to provide efficiency light harvesting in limiting light but dissipate excess potentially damaging radiation in saturating light.  The light harvesting complexes (LHCII) are central to this regulation, which is achieved by phosphorylation of stromal residues, protonation on the lumen surface and de-epoxidation of bound violaxanthin.  The functional flexibility of LHCII derives from a remarkable pigment composition and configuration which not only allow efficient absorption of light and efficient energy transfer either to PSII or PSI core complexes, but through subtle configurational changes can also exhibit highly efficient dissipative reactions involving chlorophyll-xanthophyll and/or chlorophyll-chlorophyll interactions.  These changes in function are determined at a macroscopic level by alterations in protein-protein interactions in the thylakoid membrane. The capacity and dynamics of this regulation are tuned to different physiological scenarios by the exact protein and pigment content of the light harvesting system. In this presentation the molecular mechanisms involved will be reviewed, and the optimisation of the light harvesting system in different environmental conditions described.   

• Professor Jean-David Rochaix, University of Geneva, Switzerland
• Audio recording (mp3)

Biography

Jean-David Rochaix gained a Physics diploma in 1968 from the University of Lausanne, his PhD in Biophysics in 1972 from Harvard University.  From 1972-1974 he was a post-doctoral fellow (Fogarty NIH fellowship) in the Department of Biology, Yale University.  From 1974-1981 he was Chargé de recherches, Department of Molecular Biology, University of Geneva, and since 1981 he has been Professor, Departments of Molecular Biology and Plant Biology, University of Geneva.  His departments study the biogenesis of the photosynthetic apparatus of the green unicellular alga Chlamydomonas reinhardtii and the land plant Arabidopsis using mostly molecular-genetic approaches. This process involves a concerted interplay between two genetic systems localized in the chloroplast and nucleus of the cells and is strongly influenced by environmental conditions. They also study the acclimation of plants and algae to changes in the quality and quantity of light. In this way, they have identified and characterized some of the key players in this acclimation process which are the Stt7/STN7 and Stl1/STN8 thylakoid protein kinases and the PPH1/TAB38 protein phosphatase.

Abstract 

Photosynthetic organisms are subjected to frequent changes in light quality and quantity and need to respond accordingly. These acclimatory processes are mediated to a large extent through thylakoid protein phosphorylation. Recently two major thylakoid protein kinases have been identified and characterized. The Stt7/STN7/ kinase is mainly involved in the phosphorylation of the LHCII antenna proteins and required for state transitions. It is firmly associated with the cytochrome b₆f complex and its activity is regulated by the redox state of the plastoquinone pool. The other kinase, Stl1/STN8 is responsible for the phosphorylation of the PSII core proteins. Using a reverse genetics approach we have recently identified two chloroplast protein phosphatases, PPH1/TAP38 and PBCP which counteract the activity of STN7 and STN8, respectively. Both belong to the PP2C-type phosphatase family and are conserved in land plants and algae. PBCP influences the same processes as the STN8 kinase, thylakoid membrane folding and turnover of the PSII core protein D1. The picture which emerges from these studies is that of a complex regulatory network of chloroplast protein kinases and phosphatases which is involved in light acclimation, in maintenance of the plastoquinone redox poise under fluctuating light, in the control of thylakoid protein turnover and in the adjustment to metabolic needs.

Co-authors:
Sylvain Lemeille, Alexey Shapiguzov, Iga Samol, Geoffrey Fucile, Adrian Willig and  Michel Goldschmidt-Clermont, University of Geneva, Switzerland 

• Professor Peter J Nixon, Imperial College London, UK
• Audio recording (mp3)

Biography

Peter Nixon is currently a Professor of Biochemistry within the Department of Life Sciences at Imperial College London. He has a longstanding interest in the molecular basis of solar energy conversion by chloroplasts and cyanobacteria with particular emphasis on the Photosystem II complex involved in water splitting. More recently, he and his colleagues within the Energy Futures Lab at Imperial College have begun to develop cyanobacteria, green algae and tobacco chloroplasts as solar biorefineries for the production of biofuels and other high value products.

Abstract

Despite the existence of multiple photoprotective mechanisms in vivo, visible light will ultimately cause fatal and irreversible damage to the Photosystem II (PSII) complex (so-called chronic photoinhibition).  Damaged PSII can, however, be repaired through the operation of a ‘PSII repair cycle’, which involves partial disassembly of the damaged PSII complex and the selective replacement of the damaged subunit (predominantly the D1 subunit) by a newly synthesised copy and reassembly. A key area of current research is to understand how damaged D1 is recognised and removed from the thylakoid membrane. Our recent experimental data support a model in which D1 is degraded in the cyanobacterium Synechocystis sp. PCC 6803 by a hetero-oligomeric complex composed of two different types of FtsH subunit (FtsH2 and FtsH3), with degradation proceeding from the N-terminus of D1 in a highly processive reaction [1]. We postulate that a similar mechanism of D1 degradation also operates in chloroplasts. Deg proteases are not required for D1 degradation in Synechocystis 6803 but members of this protease family appear to play a supplementary role in D1 degradation in chloroplasts.

Reference:
[1] Komenda, J, Sobotka, R and Nixon, P J (2012) Assembling and maintaining the Photosystem II complex in chloroplasts and cyanobacteria. Curr Opin Plant Biol

• Professor Eva-Mari Aro, University of Turku, Finland
• Audio recording (mp3)

Biography

Eva-Mari Aro is a professor in Molecular Plant Biology at Turku University (since 1987), and an Academy professor from 1998 to 2008. Teaching and research: plant physiology, photosynthesis and biofuel production. She has supervised 25 PhD theses in the field of photosynthetic light reactions, focusing on the biogenesis, turnover and repair of Photosystem II as well on the regulation of thylakoid dynamics by protein phosphorylation. She has been a visiting researcher at the University of California Berkeley, CSIRO Canberra, CEA Cadarache, Hebrew University and Stockholm University. She has been the president/past president of the International Society of Photosynthesis Research 2004 – 2010, and a board member of the European Plant Science Organisation. She is the Chair of the Finnish Centre of Excellence “Integrative Photosynthesis and Bioactive Compound Research at Systems Biology Level” and partner of several EU FP7 and Nordic research networks. She is an honorary professor of the Chinese Academy of Sciences.

Abstract

In sharp contrast to constant photodamage to PSII, the PSI centers are very efficiently protected against light damage, and in rare cases of damage to PSI, the subsequent recovery occurs very slowly. However, it was recently demonstrated that high light illumination can be very dangerous also to PSI. This occurs when the amount of electrons fed to the electron transfer chain (ETC) by PSII exceeds the capacity of electron acceptors on the reducing side of PSI. Plants have a capacity to regulate the relative reducing efficiencies of PSII and PSI by several different means. These include (i) the control of relative excitation of PSII and PSI, (ii) the regulation of the speed of electron transfer via the Cyt b₆f complex, and (iii) the tuning of the amount of active PSII reaction centers. We have recently shown, by using the pgr5 mutant, that in the absence of the proton gradient dependent control of Cyt b₆f, the PSI centers are very sensitive to photoinhibition. Likewise, we have shown that an accumulation in the stn7 mutant of excess electrons in intersystem ETC under low light, due to an excitation unbalance of the photosystems, is very harmful to PSI upon subsequent exposure of leaves to high light. These findings have prompted us to develop new hypotheses and theories concerning the photosensitivity of the photosynthetic apparatus and the mechanisms developed during evolution to protect the photosynthetic apparatus against photodamage.  We consider highly probable that decreasing the PSII activity upon photoinhibition is a mechanism that has developed to protect PSI against photodamage upon prolonged high light stress or under fluctuating light conditions. We will discuss about the relationships between PSII turnover, thermal dissipation of excitation energy, regulation of excitation energy distribution between PSII and PSI and the regulation of electron transfer in order to broaden the current picture on photoprotection of photosynthesis.

Co-authors:
Marjaana Suorsa, Sari Sirpiö, Michele Grieco, Markus Nurmi and Mikko Tikkanen, University of Turku, Finland 

• Professor Lixin Zhang, Institute of Botany, Chinese Academy of Sciences, China
• Audio recording (mp3)

Biography

Professor Lixin Zhang gained a BSc at Sichuan University in 1992, and a Ph Dat Lanzhou University in 1997.  Research and professional experience includes: 1997 – 2001 post-doctoral fellow, Department of biology, University of Turku, Finland ; 2000 - Research Professor, Cold and Arid Environmental Engineering Institute, Chinese Academy of Sciences; 2002 - Professor, School of Life Sciences, Lanzhou University; 2003 - Professor, Institute of Botany, Chinese Academy of Sciences; and since 2010 Deputy director, Institute of Botany, Chinese Academy of Sciences.  He is Representative of Africa, Asia, Oceania for the International Society of Photosynthesis Research (2010-), Associate Editor of Photosynthesis Research (2011-), and is a member of the editorial boards for Molecular Plant, (2008-), the Journal of Integrative Plant Biology, (2005-), Chinese Science Bulletin (2008-) and Advances in Photosynthesis and Respiration (2010-).  Research interests include chloroplast development/chloroplast gene expression; synthesis, assembly and degradation of photosynthetic protein complexes and chloroplast signal transduction

Abstract 

The major multiprotein photosynthetic complexes, located in thylakoid membranes, are responsible for the capture of light and its conversion to chemical energy in oxygenic photosynthesis organisms. Although the structure and function of these protein complexes for oxygenic photosynthesis have been extensively explored, the molecular mechanisms underlying the biogenesis and assembly of thylakoid protein complexes still remain elusive. In this review, we summarized the present knowledge regarding the regulatory components identified to be involved in the biogenesis of thylakoid protein complexes in photosynthetic organisms. The functions and their conservative mechanisms in thylakoid membrane protein complex biogenesis are discussed. Based on a wealth of information greatly benefited from the studies through genetic, transcriptomic and proteomic approaches, we attempt to integrate the well-established functions of those regulatory factors into the evolution of the structure and components of thylakoid protein complexes.

Co-author:
Wei Chi, Chinese Academy of Sciences, China

• Professor Jane Langdale, University of Oxford, UK
• Audio recording (mp3)

Biography

Jane Langdale is Professor of Plant Developmental Genetics, and Head of the Department of Plant Sciences, at the University of Oxford. Her research on chloroplast development started in the late 1980s when she worked on the genetic mechanisms underpinning dimorphic chloroplast development in the C₄ plant maize. That work led on to the identification of GLK transcription factors, that regulate chloroplast development in all land plant species studied so far. More recently she has been involved in the multi-national effort to engineer ‘C₄ rice’.

Abstract

GOLDEN2-LIKE transcription factors are required for normal chloroplast development in land plant species that encompass the range from bryophytes to angiosperms. The most obvious morphological defect in loss of function glk mutant plants is a failure to assemble thylakoids appropriately. In the flowering plant Arabidopsis thaliana, GLK proteins synchronously upregulate genes relating to light harvesting and chlorophyll biosynthesis, via direct interaction with promoter sequences. We have thus proposed that GLK activity optimizes photosynthesis by co-ordinating responses to variable environmental conditions. The direct connection between GLK activity and thylakoid assembly has yet to be established but intriguing differences between GLK function in C₃ and C₄ photosynthesising plants have led us to propose an evolutionary trajectory for GLK function.

• Professor Christine Foyer, University of Leeds, UK
• Audio recording (mp3)

Biography

Christine Helen Foyer is the Professor of Plant Sciences in Africa College and the Centre for Plant Sciences at the University of Leeds, UK. She is also an adjunct Professor at University of Western Australia, Australia and an external examiner for the University of Mauritius. She has held senior posts at Rothamsted Research (UK), the Institute of Grassland and Environmental Research (UK), the University of Newcastle upon Tyne (UK) and the Institut Nationale Recherché Agronomique (France).She has over 300 published papers and has an H-Index of 68. The Web of Knowledge for individual year counts for whole career reported 301 articles, with an average of 56.72 each. She was ranked number 7 in the top 10 list of world-wide most cited authors in Plant and Animal Sciences. Her lab uses molecular physiology approaches to understand  plant responses to environmental stresses, particularly the role of redox regulation and signalling in the control of growth and defence. She was given the annual “Founders Award” by Plant Physiology and awarded the accolade of “Redox Pioneer”, by Antioxidants and Redox Signalling.

Abstract 

Cellular redox homeostasis is a hub for signal integration. Interactions between redox metabolism and the ABSCISIC ACID (ABA)-INSENSITIVE-4 (ABI4) transcription factor were characterised in the Arabidopsis thaliana VITAMIN C DEFECTIVE 1 (vtc1)and VITAMIN C DEFECTIVE 2 (vtc2) mutants, which are defective in ascorbic acid synthesis and show a slow growth phenotype together with enhanced ABA levels relative to the wild type (Col0). The 75% decrease in the leaf ascorbate pool in the vtc2 mutants was not sufficient to adversely affect GA metabolism. The transcriptome signatures of the abi4, vtc1 and vtc2 mutants showed significant overlap, with a large number of transcription factors or signaling components similarly repressed or induced. Moreover, lincomycin-dependent changes in LIGHT HARVESTING CHLOROPHYLL A/B BINDING PROTEIN 1.1 (LHCB1.1) expression were comparable in these mutants, suggesting overlapping participation in chloroplast to nucleus signaling. The slow growth phenotype of vtc2 was absent in the abi4 vtc2 double mutant, as was the sugar insensitive phenotype of the abi4 mutant. Octadecanoid derivative-responsive AP2/ERF-domain transcription factor 47 (ORA47) and AP3 (an ABI5-binding factor) transcripts were enhanced in vtc2 but repressed in abi4 vtc2, suggesting that ABI4 and ascorbate modulate growth and defence gene expression through jasmonate signalling.

• Professor Wah Soon Chow, The Australian National University, Australia
• Audio recording (mp3)

Biography

Professor W S (Fred) Chow graduated with a PhD at The Flinders University of South Australia in 1977.  After an appointment at CSIRO Plant Industry (1977-1978), he was a Postdoctoral Fellow at the Department of Pure and Applied Biology, Imperial College London (1979-1981) and a Senior Scientific Officer, Glasshouse Crops Research Institute, Littlehampton, U.K. (1981-1985).  He then returned to Canberra to work at CSIRO Plant Industry (1985-1996), eventually as a Senior Principal Research Scientist.  From 1996 to the present, he has been doing research at The Australian National University, Canberra, where he has been a professor since 2007.

His main research interests are:

• In vivo monitoring of light-induced electron transfers in leaf photosynthesis;
• Quantification, functionality and stability of Photosystem II, which splits water into oxygen, protons and electrons during photosynthesis;
• Photoinactivation of Photosystem II;
• Acclimation of photosynthesis to the light environment;
• Cyclic electron flow around Photosystem I; and
• Entropy and entropy production in relation to chloroplast structure and function.

Abstract

Photosynthetic membrane sacs (thylakoids) of plants form granal stacks interconnected by non-stacked thylakoids, thereby being able to fine-tune photosynthesis.  Growth in low light leads to the formation of large grana, which sometimes contain as many as 160 thylakoids.  The net surface charge of thylakoid membranes is negative, even in low-light-grown plants, so an attractive force is required to overcome the electrostatic repulsion.  The theoretical van der Waals attraction is, however, at least 20-fold too small to play the role.  We determined the enthalpy change, in the spontaneous stacking of previously unstacked thylakoids on addition of Mg²⁺, to be zero or marginally positive (endothermic).  The Gibbs free energy change for the spontaneous process is necessarily negative; therefore, an increase in entropy is the only way to achieve such a negative Gibbs free energy change.  We conclude that the dominant attractive force in thylakoid stacking is entropy-driven.  Some mechanisms for increasing entropy upon stacking of thylakoid membranes, particularly in low-light plants, are discussed.

Co-authors:
Husen Jia, John R Liggins, The Australian National University, Australia

• Professor Charles Barry Osmond FRS, The Australian National University and University of Wollongong, Australia
• Audio recording (mp3)

Biography

Barry Osmond is a well known Australian plant biologist (PhD Adelaide 1963-65). His career in photosynthetic ecophysiology emerged from the unparalleled opportunities formerly available in the Research School of Biological Sciences, Institute of Advanced Studies, Australian National University (1967-2001). He was Director, Biosciences Center, Desert Research Institute, University of Nevada Reno (1981-86) and Arts and Sciences Distinguished Professor, Department of Botany, Duke University (1987-91) before returning to Australia as Director RSBS and leader of the Photobioenergetics Research Group (1991-1998). Resigning from ANU in 2001, he moved to Columbia University’s visionary Biosphere 2 Center to promote new approaches in experimental ecosystem and climate change science, now described in some 70 publications arising from research 1998-2003. In retirement he is an Honorary Visiting Fellow at ANU and holds a fractional appointment in the University of Wollongong where he continues research on inner canopy leaves of woody plants as they grow old in the shade.

Abstract

Ever since the pioneering studies of shade-sun acclimation in-vivo (Björkman & Holmgren 1963), the discovery of huge grana in the shade plant Alocasia (Goodchild et al 1972) and analyses of electron transport in thylakoid membranes of isolated pea chloroplasts in response to light intensities during growth (Leong & Anderson 1984), physiological studies in diverse plants have presented reality checks for contemporary understanding of the dynamics of these membrane systems. This paper presents new physiological data from in-vivo chlorophyll fluorescence analyses on the time frames of the slow coordinated photosynthetic development of sink leaves, and on slow renovation of photosynthetic properties of old leaves during sun to shade and shade to sun acclimation in the canopies of woody plants. It also focuses on pigment dynamics in relation to photoprotection in avocado, especially those encouraging further attention to the role of lutein epoxide and lutein in light harvesting and photoprotection in shade leaves. In so doing it grapples with issues in-vivo that seem relevant to our increasingly sophisticated understanding of ΔpH-dependent, xanthophyll pigment stabilized non-photochemical quenching (NPQ) in the antennae of PSII in thylakoid membranes in-vitro. 

Coauthors:
Britta Förster, The Australian National University, Australia
Shizue Matsubara, IBG-2: Pflanzenwissenschaften, Forschungszentrum Jülich, Germany
Melinda Waterman, University of Wollongong, Australia
Brian E S Gunning, The Australian National University, Australia
Barry J Pogson, The Australian National University, Australia