Cyanobacterial psbA gene family: optimization of oxygenic photosynthesis

The D1 protein of Photosystem II (PSII), encoded by the psbA genes, is an indispensable component of oxygenic photosynthesis. Due to strongly oxidative chemistry of PSII water splitting, the D1 protein is prone to constant photodamage requiring its replacement, whereas most of the other PSII subunits remain ordinarily undamaged. In cyanobacteria, the D1 protein is encoded by a psbA gene family, whose members are differentially expressed according to environmental cues. Here, the regulation of the psbA gene expression is first discussed with emphasis on the model organisms Synechococcus sp. and Synechocystis sp. Then, a general classification of cyanobacterial D1 isoforms in various cyanobacterial species into D1m, D1:1, D1:2, and D1′ forms depending on their expression pattern under acclimated growth conditions and upon stress is discussed, taking into consideration the phototolerance of different D1 forms and the expression conditions of respective members of the psbA gene family

Photosystem II repair in plant chloroplasts — Regulation, assisting proteins and shared components with photosystem II biogenesis

AbstractPhotosystem (PS) II is a multisubunit thylakoid membrane pigment–protein complex responsible for light-driven oxidation of water and reduction of plastoquinone. Currently more than 40 proteins are known to associate with PSII, either stably or transiently. The inherent feature of the PSII complex is its vulnerability in light, with the damage mainly targeted to one of its core proteins, the D1 protein. The repair of the damaged D1 protein, i.e. the repair cycle of PSII, initiates in the grana stacks where the damage generally takes place, but subsequently continues in non-appressed thylakoid domains, where many steps are common for both the repair and de novo assembly of PSII. The sequence of the (re)assembly steps of genuine PSII subunits is relatively well-characterized in higher plants. A number of novel findings have shed light into the regulation mechanisms of lateral migration of PSII subcomplexes and the repair as well as the (re)assembly of the complex. Besides the utmost importance of the PSII repair cycle for the maintenance of PSII functionality, recent research has pointed out that the maintenance of PSI is closely dependent on regulation of the PSII repair cycle. This review focuses on the current knowledge of regulation of the repair cycle of PSII in higher plant chloroplasts. Particular emphasis is paid on sequential assembly steps of PSII and the function of the number of PSII auxiliary proteins involved both in the biogenesis and repair of PSII. This article is part of a Special Issue entitled: Chloroplast Biogenesis

Model for the Fluorescence Induction Curve of Photoinhibited Thylakoids

AbstractThe fluorescence induction curve of photoinhibited thylakoids measured in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethyl urea was modeled using an extension of the model of Lavergne and Trissl (Biophys. J. 68:2474–2492), which takes into account the reversible exciton trapping by photosystem II (PSII) reaction centers and exciton exchange between PSII units. The model of Trissl and Lavergne was modified by assuming that PSII consists of photosynthetically active and photoinhibited (inactive in oxygen evolution) units and that the inactive PSII units can efficiently dissipate energy even if they still retain the capacity for the charge separation reaction. Comparison of theoretical and experimental fluorescence induction curves of thylakoids, which had been subjected to strong light in the presence of the uncoupler nigericin, suggests connectivity between the photoinhibited and active PSII units. The model predicts that photoinhibition lowers the yield of radical pair formation in the remaining active PSII centers. However, the kinetics of PSII inactivation in nigericin-treated thylakoids upon exposure to photoinhibitory light ranging from 185 to 2650μmol photons m−2 s−1 was strictly exponential. This may suggest that photoinhibition occurs independently of the primary electron transfer reactions of PSII or that increased production of harmful substances by photoinhibited PSII units compensates for the protection afforded by the quenching of excitation energy in photoinhibited centers

Koulu-uudistuksen käyntiinpanon unohdetut arkkitehdit

Koulu-uudistusprosessin liikkeellelähtö 1960-luvun alussa tapahtui paljolti yksittäisten kansalaisten ja vapaiden kansalaisjärjestöjen aktiivisuuden pohjalta. Me kirjoittajat elimme lapsuutemme ja nuoruutemme koulu-uudistuksen sydämessä 1950-luvulta lähtien. Perehdyttyämme isämme Onni Niemen jäämistöön valotamme tässä artikkelissa kahden yksityishenkilön, diplomi-insinööri Aarne Hellemaan ja filosofian tohtori Onni Niemen, uraauurtavaa työtä koulunuudistusprosessin käyntiinpanossa Suomessa

True oxygen reduction capacity during photosynthetic electron transfer in thylakoids and intact leaves

Photosynthetically derived H2O2 only accumulates at Photosystem I and may trigger cooperation with mitochondria during stress.Reactive oxygen species (ROS) are generated in electron transport processes of living organisms in oxygenic environments. Chloroplasts are plant bioenergetics hubs where imbalances between photosynthetic inputs and outputs drive ROS generation upon changing environmental conditions. Plants have harnessed various site-specific thylakoid membrane ROS products into environmental sensory signals. Our current understanding of ROS production in thylakoids suggests that oxygen (O-2) reduction takes place at numerous components of the photosynthetic electron transfer chain (PETC). To refine models of site-specific O-2 reduction capacity of various PETC components in isolated thylakoids of Arabidopsis thaliana, we quantified the stoichiometry of oxygen production and consumption reactions associated with hydrogen peroxide (H2O2) accumulation using membrane inlet mass spectrometry and specific inhibitors. Combined with P700 spectroscopy and electron paramagnetic resonance spin trapping, we demonstrate that electron flow to photosystem I (PSI) is essential for H2O2 accumulation during the photosynthetic linear electron transport process. Further leaf disc measurements provided clues that H2O2 from PETC has a potential of increasing mitochondrial respiration and CO2 release. Based on gas exchange analyses in control, site-specific inhibitor-, methyl viologen-, and catalase-treated thylakoids, we provide compelling evidence of no contribution of plastoquinone pool or cytochrome b6f to chloroplastic H2O2 accumulation. The putative production of H2O2 in any PETC location other than PSI is rapidly quenched and therefore cannot function in H2O2 translocation to another cellular location or in signaling

D1 protein degradation during photoinhibition of intact leaves a modification of the D1 protein precedes degradation

AbstractIllumination of intact pumpkin leaves with high light led to severe photoinhibition of photosystem II with no net degradation of the D1 protein. Instead, however, a modified form of D1 protein with slightly slower electrophoretic mobility was induced with corresponding loss in the original form of the D1 protein. When the leaves were illuminated in the presence of chloramphenicol the modified form was degraded, which led to a decrease in the total amount of the D1 protein. Subfractionation of the thylakoid membranes further supported the conclusion that the novel form of the D1 protein was not a precursor but a high-light modified form that was subsequently degraded

SRM dataset of the proteome of inactivated iron-sulfur cluster biogenesis regulator SufR in Synechocystis sp. PCC 6803

This article contains SRM proteomics data related to the research article entitled ”Inactivation of iron-sulfur cluster biogenesis regulator SufR in Synechocystis sp. PCC 6803 induces unique iron-dependent protein-level responses”[1]. The data described here provide comprehensive information on the applied SRM assays, together with the results of quantifying 94 Synechocystis sp. PCC 6803 proteins.  The data has been deposited in Panorama public  (https://panoramaweb.org/labkey/SufR) and from PASSEL under the PASS00765 identifier (http://www.peptideatlas.org/PASS/PASS00765).  </p