STATE TRANSITION7-Dependent Phosphorylation Is Modulated by Changing Environmental Conditions, and Its Absence Triggers Remodeling of Photosynthetic Protein Complexes

In plants and algae, the serine/threonine kinase STN7/STT7, orthologous protein kinases in Chlamydomonas reinhardtii and Arabidopsis (Arabidopsis thaliana), respectively, is an important regulator in acclimation to changing light environments. In this work, we assessed STT7-dependent protein phosphorylation under high light in C. reinhardtii, known to fully induce the expression of light-harvesting complex stress-related protein3 (LHCSR3) and a nonphotochemical quenching mechanism, in relationship to anoxia where the activity of cyclic electron flow is stimulated. Our quantitative proteomics data revealed numerous unique STT7 protein substrates and STT7-dependent protein phosphorylation variations that were reliant on the environmental condition. These results indicate that STT7-dependent phosphorylation is modulated by the environment and point to an intricate chloroplast phosphorylation network responding in a highly sensitive and dynamic manner to environmental cues and alterations in kinase function. Functionally, the absence of the STT7 kinase triggered changes in protein expression and photoinhibition of photosystem I (PSI) and resulted in the remodeling of photosynthetic complexes. This remodeling initiated a pronounced association of LHCSR3 with PSI-light harvesting complex I (LHCI)-ferredoxin-NADPH oxidoreductase supercomplexes. Lack of STT7 kinase strongly diminished PSII-LHCII supercomplexes, while PSII core complex phosphorylation and accumulation were significantly enhanced. In conclusion, our study provides strong evidence that the regulation of protein phosphorylation is critical for driving successful acclimation to high light and anoxic growth environments and gives new insights into acclimation strategies to these environmental conditions

Association of Ferredoxin:NADP+ oxidoreductase with the photosynthetic apparatus modulates electron transfer in Chlamydomonas reinhardtii

R.M. acknowledges support from the MEXT (Ministry of Education, Culture, Sports, Science and Technology, 15K21122). T.H. gratefully acknowledges support from the DFG (DIP project cooperation “Nanoengineered optoelectronics with biomaterials and bioinspired assemblies”) and the Volkswagen Foundation (LigH2t). G.K. acknowledges support from CREST, Japan Science and Technology Agency. M.H. acknowledges support from the DFG (Deutsche Forschungsgemeinschaft, HI 739/13-1)

Association of Early Repolarization Pattern on ECG with Risk of Cardiac and All-Cause Mortality: A Population-Based Prospective Cohort Study (MONICA/KORA)

In a population-based cohort study of middle-aged people in Central Europe, Stefan Kääb and colleagues find an association between electrocardiographic early repolarization pattern and mortality risk

Thylakoid Ultrastructure: Visualizing the Photosynthetic Machinery

The surface of our planet receives ∼3020 ZJ per year of solar energy annually, which is >5000 times the energy required to power our entire global economy (∼0.6 ZJ per year). Of this energy, ∼43% is photosynthetic active light radiation (PAR) that can be used to drive microalgal biotechnologies for the production of food, fuels, high value products, carbon sequestration, and bioremediation. The first step of all light-driven microalgal processes is light capture. A diverse array of highly efficient, self-assembling, light-responsive “solar interfaces,” the thylakoid membranes, have evolved to tap into this abundant, but constantly changing, energy resource to power the biosphere. The photosynthetic machinery within the thylakoids is intricately arranged in a complex 3D architecture and designed to adapt dynamically (i.e., 4D: representing changes in 3D structures over time) to constantly changing environmental conditions, to maximize solar to chemical energy conversion. The ATP and NADPH generated are used to produce the complex set of biomolecules that collectively form biomass. Here, we review the structural organization of these amazing photosynthetic interfaces in the model organism Chlamydomonas reinhardtii and summarize recent advances in structural biology, which underpin the development of next-generation atomic resolution dynamic simulations of these systems. Revealing such a 4D atlas of 3D structures in atomic resolution detail is of fundamental importance to enable structure-guided design of natural photosynthetic systems for biotechnological application and to provide a blueprint for the design of nanoscale components, which are the building blocks for the development of next-generation artificial solar fuel systems.They are also thankful to the University of Rouen, the region Haute-Normandie now called Normandie and the IUF for their financial support

Mitochondria affects photosynthetic electron transport and photo-sensitivity in a green alga

Photosynthetic organisms use sunlight as the primary source of energy to support their metabolism. In eukaryotes reactions responsible of the conversion of light into chemical energy occur in specific organelles, the chloroplasts. In this study we showed that mitochondria also have a seminal influence on cells' energy metabolism and on photosynthetic reactions. This is illustrated by the observation that the strong photosensitivity of Chlamydomonas reinhardtii cells depleted of the chloroplast protein PGRL1 was rescued by the introduction of a mitochondrial mutation affecting respiratory complex I. Functional analysis showed that such a reduced respiratory activity influenced chloroplast electron transport with consequent over-reduction of plastoquinone and donor-side limitation of Photosystem (PS) I. As a consequence, damage due to excess light affected more Photosystem (PS) II rather than PSI. Double mutant cells are able to grow under excess illumination, while single pgrl1 are not, thanks to the presence of an efficient repair mechanism of Photosystem II. These results also underline the seminal biological relevance of the regulation of electron transport reactions within the photosynthetic complexes. Photosynthetic organisms evolved a strategy to respond to excess light where damage is targeting preferentially to a specific complex, PSII. Cells are able to endure extensive damage targeting this complex thanks to an efficient repair mechanisms while, if PSI is affected there are drastic consequences on growth

Proton Gradient Regulation5-Like1-Mediated Cyclic Electron Flow Is Crucial for Acclimation to Anoxia and Complementary to Nonphotochemical Quenching in Stress Adaptation

International audienceTo investigate the functional importance of Proton Gradient Regulation5-Like1 (PGRL1) for photosynthetic performances in the moss Physcomitrella patens, we generated a pgrl1 knockout mutant. Functional analysis revealed diminished nonphotochemical quenching (NPQ) as well as decreased capacity for cyclic electron flow (CEF) in pgrl1. Under anoxia, where CEF is induced, quantitative proteomics evidenced severe down-regulation of photosystems but up-regulation of the chloroplast NADH dehydrogenase complex, plastocyanin, and Ca(2+) sensors in the mutant, indicating that the absence of PGRL1 triggered a mechanism compensatory for diminished CEF. On the other hand, proteins required for NPQ, such as light-harvesting complex stress-related protein1 (LHCSR1), violaxanthin de-epoxidase, and PSII subunit S, remained stable. To further investigate the interrelation between CEF and NPQ, we generated a pgrl1 npq4 double mutant in the green alga Chlamydomonas reinhardtii lacking both PGRL1 and LHCSR3 expression. Phenotypic comparative analyses of this double mutant, together with the single knockout strains and with the P. patens pgrl1, demonstrated that PGRL1 is crucial for acclimation to high light and anoxia in both organisms. Moreover, the data generated for the C. reinhardtii double mutant clearly showed a complementary role of PGRL1 and LHCSR3 in managing high light stress response. We conclude that both proteins are needed for photoprotection and for survival under low oxygen, underpinning a tight link between CEF and NPQ in oxygenic photosynthesis. Given the complementarity of the energy-dependent component of NPQ (qE) and PGRL1-mediated CEF, we suggest that PGRL1 is a capacitor linked to the evolution of the PSII subunit S-dependent qE in terrestrial plants

Deletion of Proton Gradient Regulation 5 (PGR5) and PGR5-Like 1 (PGRL1) proteins promote sustainable light-driven hydrogen production in Chlamydomonas reinhardtii due to increased PSII activity under sulfur deprivation

International audienc