Current crop yields will not be enough to sustain today's diets for a growing global population. As plant photosynthetic efficiency has not reached its theoretical maximum, optimizing photosynthesis is a promising strategy to enhance plant productivity. The low productivity of C 3 plants is caused in part by the substantial energetic investments necessary to maintain a high flux through the photorespiratory pathway. Accordingly, lowering the energetic costs of photorespiration to enhance the productivity of C 3 crops has been a goal of synthetic plant biology for decades. The use of synthetic bypasses to photorespiration in different plants showed an improvement of photosynthetic performance and growth under laboratory and field conditions, even though in silico predictions suggest that the tested synthetic pathways should confer a minimal or even negative energetic advantage over the wild type photorespiratory pathway. Current strategies increasingly utilize theoretical modeling and new molecular techniques to develop synthetic biochemical pathways that bypass photorespiration, representing a highly promising approach to enhance future plant productivity.

Photosynthesis is fundamental to biomass production, but is a dynamic process sensitive to environmental constraints. In recent years, approaches to increase biomass and grain yield by altering photosynthetically related processes in the plant have received considerable attention. However, improving biomass yield requires a predictive understanding of the molecular mechanisms that allow photosynthesis to be adjusted. The important roles of metabolic reactions external to those directly involved in photosynthesis are highlighted in this review; however, our major focus is on the routes taken to improve photosynthetic carbon assimilation and to increase photosynthetic efficiency and consequently biomass yield.

Plant photosystem I (PSI) is one of the most intricate membrane complexes in nature. It comprises two complexes, a reaction center and light-harvesting complex (LHC), which together form the PSI–LHC supercomplex. The crystal structure of plant PSI was solved with two distinct crystal forms. The first, crystallized at pH 6.5, exhibited P 21 symmetry; the second, crystallized at pH 8.5, exhibited P 212121 symmetry. The surfaces involved in binding plastocyanin and ferredoxin are identical in both forms. The crystal structure at 2.6 Å resolution revealed 16 subunits, 45 transmembrane helices, and 232 prosthetic groups, including 143 chlorophyll a , 13 chlorophyll b , 27 β-carotene, 7 lutein, 2 xanthophyll, 1 zeaxanthin, 20 monogalactosyl diglyceride, 7 phosphatidyl diglyceride, 5 digalactosyl diglyceride, 2 calcium ions, 2 phylloquinone, and 3 iron sulfur clusters. The model reveals detailed interactions, providing mechanisms for excitation energy transfer and its modulation in one of nature's most efficient photochemical machine.

Along with the development of several large-scale methods such as mass spectrometry or micro arrays, genome wide models became not only a possibility but an obvious tool for theoretical biologists to integrate and analyse complex biological data. Nevertheless, incorporating the dynamics of photosynthesis remains one of the major challenges while reconstructing metabolic networks of plants and other photosynthetic organisms. In this review, we aim to provide arguments that small-scale models are still a suitable choice when it comes to discovering organisational principles governing the design of biological systems. We give a brief overview of recent modelling efforts in understanding the interplay between rapid, photoprotective mechanisms and the redox balance within the thylakoid membrane, discussing the applicability of a reductionist approach in modelling self-regulation in plants and outline possible directions for further research.

In the present paper, we review the toxicity of sugar- and lipid-derived RCs (reactive carbonyls) and the RC-scavenging systems observed in photosynthetic organisms. Similar to heterotrophs, photosynthetic organisms are exposed to the danger of RCs produced in sugar metabolism during both respiration and photosynthesis. RCs such as methylglyoxal and acrolein have toxic effects on the photosynthetic activity of higher plants and cyanobacteria. These toxic effects are assumed to occur uniquely in photosynthetic organisms, suggesting that RC-scavenging systems are essential for their survival. The aldo–keto reductase and the glyoxalase systems mainly scavenge sugar-derived RCs in higher plants and cyanobacteria. 2-Alkenal reductase and alkenal/alkenone reductase catalyse the reduction of lipid-derived RCs in higher plants. In cyanobacteria, medium-chain dehydrogenases/reductases are the main scavengers of lipid-derived RCs.

Molecular bioenergetics deals with the construction, function and regulation of the powerhouses of life. The present overview sketches scenes and actors, farsighted goals and daring hypotheses, meticulous tool-making, painstaking benchwork, lucky discovery, serious scepticism, emphatic believing and strong characters with weak and others with hard arguments, told from a personal, admittedly limited, perspective. Bioenergetics will blossom further with the search focused on both where there is bright light for ever-finer detail and the obvious dark spots for surprise and discovery.

A large variety of new energy-generating technologies are being developed in an effort to reduce global dependence on fossil fuels, and to reduce the carbon footprint of energy generation. The term ‘biological photovoltaic system’ encompasses a broad range of technologies which all employ biological material that can harness light energy to split water, and then transfer the resulting electrons to an anode for power generation or electrosynthesis. The use of whole cyanobacterial cells is a good compromise between the requirements of the biological material to be simply organized and transfer electrons efficiently to the anode, and also to be robust and able to self-assemble and self-repair. The principle that photosynthetic bacteria can generate and transfer electrons directly or indirectly to an anode has been demonstrated by a number of groups, although the power output obtained from these devices is too low for biological photovoltaic devices to be useful outside the laboratory. Understanding how photosynthetically generated electrons are transferred through and out of the organism is key to improving power output, and investigations on this aspect of the technology are the main focus of the present review.

Protection against strong-light-induced photodamage of the photosynthetic apparatus and entire organisms is a vital activity in plants and is also realized at the molecular level of the antenna complexes. Reported recently, the regulatory mechanisms which operate in the largest plant antenna complex, LHCII (light-harvesting complex II), based on light-driven processes, are briefly reviewed and discussed. Among those processes are the light-induced twisting of the configuration of the LHCII-bound neoxanthin, the light-induced configurational transition of the LHCII-bound violaxanthin, the light-induced trimer–monomer transition in LHCII and the blue-light-induced excitation quenching in LHCII. The physiological importance of the processes reviewed is also discussed with emphasis on the photoprotective excitation quenching and on possible involvement in the regulation of the xanthophyll cycle.

Photoreaction centres are Nature's solar batteries. These nanometre-scale power producers are responsible for transducing the energy of sunlight into a form that can be used by biological systems, thereby powering most of the biological activity on the planet. Although to the layman the word ‘photosynthesis’ is usually associated with green plants, much of our understanding of the molecular basis of biological transduction of light energy has come from studies of purple photosynthetic bacteria. Their RCs (reaction centres) and attendant light-harvesting complexes have been subjected to an intensive spectroscopic scrutiny, coupled with genetic manipulation and structural studies, that has revealed many of the molecular and mechanistic details of biological energy transfer, electron transfer and coupled proton translocation. This review provides a short overview of the structure and mechanism of the purple bacterial RC, focusing in the main on the most heavily studied complex from Rhodobacter sphaeroides .

This review presents a broad overview of phosphorylation and signalling in plants. Much of the work of my group in plants focuses on understanding the mechanisms that regulate the production of carbon and nitrogen metabolites in leaves; in this review, I will discuss nitrate, which is one of the most important of these inorganic nutrients. I also detail how protein phosphorylation in plant cells is altered in response to the presence of reactive oxygen species.

Photosystem II (PSII) is a multisubunit enzyme embedded in the lipid environment of the thylakoid membranes of plants, algae and cyanobacteria. Powered by light, this enzyme catalyses the chemically and thermodynamically demanding reaction of water splitting. In so doing, it releases dioxygen into the atmosphere and provides the reducing equivalents required for the conversion of CO 2 into the organic molecules of life. Recently, a fully refined structure of a 700 kDa cyanobacterial dimeric PSII complex was elucidated by X-ray crystallography which gave organizational and structural details of the 19 subunits (16 intrinsic and three extrinsic) which make up each monomer and provided information about the position and protein environments of 57 different cofactors. The water-splitting site was revealed as a cluster of four Mn ions and a Ca 2+ ion surrounded by amino acid side chains, of which six or seven form direct ligands to the metals. The metal cluster was modelled as a cubane-like structure composed of three Mn ions and the Ca 2+ linked by oxo-bonds with the fourth Mn attached to the cubane via one of its oxygens. The overall structure of the catalytic site is providing a framework to develop a mechanistic scheme for the water-splitting process, knowledge which could have significant implications for mimicking the reaction in an artificial chemical system.

One-carbon transfer reactions are mediated by H 4 F (tetrahydrofolate), a soluble coenzyme (vitamin B 9 ) that is synthesized de novo by plants and microorganisms, and absorbed from the diet by animals. H 4 F synthesis in plants is quartered between the plastids, the cytosol and the mitochondria, a spatial distribution that is not observed in the other organisms and that suggests a complex intracellular traffic. Also, the activity of H 4 F synthesis fluctuates during plant growth, depending on the tissue and the developmental stage of the seedling, thus illustrating the flexibility of one-carbon metabolism in these organisms. This paper will focus on our recent knowledge about H 4 F synthesis in the plant cell and will briefly describe the activity of the pathway during the growth and development of the seedling.

Regulation of photosynthetic membrane synthesis in Rhodobacter sphaeroides 2.4.1 is dependent on the interactions of numerous regulatory elements, with two of the most important being the cbb 3 terminal oxidase and the PrrBAC two-component regulatory system. Here, we reveal that the cbb 3 terminal oxidase possesses extensive, additional regulatory activities under anaerobic conditions, and that the PrrBAC system is further involved in the regulation of the expression of more than 20% of the R. sphaeroides genome under anaerobic conditions, extending well beyond functions related to redox gene expression.

We are using a molecular-genetic approach to investigate the role of nuclear genes in the biogenesis of the electron transfer complexes of mitochondria and chloroplasts. Our analysis of nuclear mutants of the green alga Chlamydomonas that are defective in respiration or photosynthesis has led to the identification of genes encoding factors required for the expression of specific organellar genes, and genes encoding structural components of the complexes.

Redox chemistry is central to the primary functions of chloroplasts and mitochondria, that is, to energy conversion in photosynthesis and respiration. However, these bioenergetic organelles always contain very small, specialized genetic systems, relics of their bacterial origin. At huge cost, organellar genomes contain, typically, a mere 0.1 % of the genetic information in a eukaryotic cell. There is evidence that chloroplast and mitochondrial genomes encode proteins whose function and biogenesis are particularly tightly governed by electron transfer. We have identified nuclear genes for ‘bacterial’ histidine sensor kinases and aspartate response regulators that seem to be targeted to chloroplast and mitochondrial membranes. Sequence similarities to cyano-bacterial redox signalling components indicate homology and suggest conserved sensory and signalling functions. Two-component redox signalling pathways might be ancient, conserved mechanisms that permit endogenous control over the biogenesis, in situ , of bioenergetic complexes of chloroplasts and mitochondria.

Oxygenic photosynthesis can be described effectively by using two long-standing models: the Z-scheme and the chemiosmotic hypothesis. However, these models do not reveal the dynamic nature of the thylakoid membrane and the four major complexes that it binds. The composition of the photosynthetic apparatus is continually changing in response to a range of environmental stimuli. In addition, many photosynthetic components have some of the highest turnover rates in Nature. Changes in composition and turnover of photosynthetic components require the degradation of existing and damaged polypeptides and the resynthesis and co-ordinated assembly of new polypeptides and their associated cofactors. This is achieved by several auxiliary functions, including proteolysis, protein targeting and the action of molecular chaperones. Some of the components involved in these functions, such as translocons, chaperones and proteases, have been identified but many of the auxiliary functions of photosynthesis remain uncharacterized. Among the proteases known to be associated with the thylakoids is the zinc metalloprotease FtsH, which might also act as a chaperone. Here we provide an overview of the thylakoid FtsH protease and discuss its role in the maintenance and assembly of the photosynthetic apparatus.