The High Light Response in Arabidopsis Requires the Calcium Sensor Protein CAS, a Target of STN7-and STN8-Mediated Phosphorylation

Reversible phosphorylation of thylakoid proteins contributes to photoacclimation responses in photosynthetic organisms, enabling the fine-tuning of light harvesting under changing light conditions and promoting the onset of photoprotective processes. However, the precise functional role of many of the described phosphorylation events on thylakoid proteins remains elusive. The calcium sensor receptor protein (CAS) has previously been indicated as one of the targets of the state transition kinase 8 (STN8). Here we show that in Arabidopsis thaliana, CAS is also phosphorylated by the state transition kinase 7 (STN7), as well as by another, so-far unknown, Ca2+-dependent kinase. Phosphoproteomics analysis and in vitro phosphorylation assays on CAS variants identified the phylogenetically conserved residues Thr-376, Ser-378, and Thr-380 as the major phosphorylation sites of the STN kinases. Spectroscopic analyses of chlorophyll fluorescence emission at 77K further showed that, while the cas mutant is not affected in state transition, it displays a persistent strong excitation of PSI under high light exposure, similar to the phenotype previously observed in other mutants defective in photoacclimation mechanisms. Together with the observation of a strong concomitant phosphorylation of light harvesting complex II (LHCII) and photosynthetic core proteins under high irradiance in the cas mutant this suggests a role for CAS in the STN7/STN8/TAP38 network of phosphorylation-mediated photoacclimation processes in Arabidopsis

Belgio

One of the most common reactive oxygen species (ROS) produced in eukaryotic organisms during photosynthesis is hydrogen peroxide (H2O2) [1]. To evaluate the impact of H2O2-scavenging enzymes on algal fitness, we selected a mutant deficient in ascorbate peroxidase 2 (APX2) in the green microalga Chlamydomonas reinhardtii. Ascorbate peroxidase (APX) uses ascorbate and H2O2 as substrates to form monodehydroascorbate (MDHA) and H2O. The enzyme, encoded by eight isoforms in Arabidopsis thaliana, has been already well-described in plants as one of the main actors involved in the Mehler reaction in which electrons obtained from H2O oxidation in photosystem II (PSII) are linearly transported to the acceptor side of photosystem I (PSI) where they are used to completely reduce the superoxide (O2-) to H2O [2]. In Chlamydomonas, four APX isoforms are present and APX2 is predicted to be targeted to the thylakoid membrane of the chloroplast using Target P [3]. In this study, we focus on the importance of APX2 in the Mehler reaction and during linear electron flow. To assess these two functionalities of APX2, we evaluated photosynthetic parameters under control light and high light in cells grown phototrophically and mixotrophically. Therefore, we compared the quantum yield of PSII (φPSII) by monitoring in vivo chlorophyll a fluorescence, and the photooxidation and the re-reduction rate of the PSI of wild type (WT) and apx2 mutant cells. We found that the effects of the loss of APX2 are mainly seen in cells grown phototrophically in control light. The apx2 mutant cells present a decreased rate of the relative electron transport (rETR) in phototrophic control light growth condition and the PSII efficiency resembles the one of WT under high light or H2O2 stress. We also observed a higher PSI photooxidation rate for the apx2 mutant compared to WT in cells grown phototrophically in control light, suggesting an electron donor side limitation at the level of the PSI. Further, the lower re-reduction rate of the PSI in apx2 mutant compared to the WT after a short pulse of saturating light supports our observations. All in all, the APX2 enzyme seems to exert its function under unstressful physiological condition and could be involved in the early redox poise of photosynthesis. Funded by FNRS-FWO EOS Project 30829584 [1] Asada, Plant Physiol. 141, 391 – 396 (2006) [2] Dietz et al., J. Exp. Bot. 53, 1321 – 1329 (2002) [3] Emanuelsson et al., J. Mol. Biol. 300, 4, 1005 – 106 (2000

Merged Heme and Non-Heme Manganese Co-Factors for a Dual Anti-Oxidant Surveillance in Photosynthetic Organisms

The coupling of a polycationic Mn(III)-porphyrin, with a dinuclear Mn2(II,II)L2 core (HL = 2-{[[di(2-pyridyl)methyl](methyl)amino]methyl}phenol), results in a dual Superoxide Dismutase (SOD) and Catalase (CAT) functional analogue, Mn2L2Pn+, enabling a detoxification cascade of the superoxide anion and hydrogen peroxide into benign H2O and O2. The SOD/CAT artificial manifolds, joined in one asset, exhibit a peak catalytic performance under physiological conditions, with log kcat(O2\u2022\u202f\u2013) 65 7 and kcat(H2O2)/KM = 1890. The dual-enzyme (dizyme) concept allows for a built-in self-protection against the irreversible bleaching of the porphyrin unit (>75% protection), readily induced by H2O2 (200 \u3bcM, 20 equiv, in buffer solution, pH 7.8). We show herein that incubation of the photosynthetic green algae, Chlamydomonas reinhardtii, with the synthetic dizyme (as low as 0.1 \u3bcM), prevents H2O2 accumulation under high-light illumination conditions, thus providing antioxidant surveillance and photoprotection

Lipid management in contemporary community practice: Results from the Provider Assessment of Lipid Management (PALM) Registry

Background: The latest cholesterol guidelines have shifted focus from achieving low-density lipoprotein cholesterol (LDL-C) targets toward statin use and intensity guided by atherosclerotic cardiovascular disease (ASCVD) risk. Methods: Statin use and intensity were evaluated in 5,905 statin-eligible primary or secondary prevention patients from 138 PALM Registry practices. Results: Overall, 74.7% of eligible adults were on statins; only 42.4% were on guideline-recommended intensity. Relative to primary prevention patients, ASCVD patients were more likely to be on a statin (83.6% vs 63.4%, P\u3c.0001) and guideline-recommended intensity (47.3% vs 36.0%, P\u3c.0001). Men were more likely than women to be prescribed recommended intensity for primary (odds ratio [OR] 1.87, 95% CI 1.49-2.34) and secondary (OR 1.47, 95% CI 1.26-1.70) prevention. In primary prevention, increasing age, diabetes, obesity, hypertension, and lower 10-year ASCVD risk were associated with increased odds of receiving recommended intensity. Among ASCVD patients, those with coronary artery disease were more likely to be on recommended intensity than cerebrovascular or peripheral vascular disease patients (OR 1.71, 95% CI 1.41-2.09), as were those seen by cardiologists (OR 1.43, 95% CI 1.12-1.83). Median LDL-C levels were highest among patients not on statins (124.0 mg/dL) and slightly higher among those on lower-than-recommended intensity compared with recommended-therapy recipients (88.0 and 84.0 mg/dL, respectively; P≤.0001). Conclusions: In routine contemporary practice, 1 in 4 guideline-eligible patients was not on a statin; less than half were on the recommended statin intensity. Untreated and undertreated patients had significantly higher LDL-C levels than those receiving guideline-directed statin treatmen

KM3NeT front-end and readout electronics system: hardware, firmware, and software

he KM3NeT research infrastructure being built at the bottom of the Mediterranean Sea will host water-Cherenkov telescopes for the detection of cosmic neutrinos. The neutrino telescopes will consist of large volume three-dimensional grids of optical modules to detect the Cherenkov light from charged particles produced by neutrino-induced interactions. Each optical module houses 31 3-in. photomultiplier tubes, instrumentation for calibration of the photomultiplier signal and positioning of the optical module, and all associated electronics boards. By design, the total electrical power consumption of an optical module has been capped at seven Watts. We present an overview of the front-end and readout electronics system inside the optical module, which has been designed for a 1-ns synchronization between the clocks of all optical modules in the grid during a life time of at least 20 years

Architecture and performance of the KM3NeT front-end firmware

The KM3NeT infrastructure consists of two deep-sea neutrino telescopes being deployed in the Mediterranean Sea. The telescopes will detect extraterrestrial and atmospheric neutrinos by means of the incident photons induced by the passage of relativistic charged particles through the seawater as a consequence of a neutrino interaction. The telescopes are configured in a three-dimensional grid of digital optical modules, each hosting 31 photomultipliers. The photomultiplier signals produced by the incident Cherenkov photons are converted into digital information consisting of the integrated pulse duration and the time at which it surpasses a chosen threshold. The digitization is done by means of time to digital converters (TDCs) embedded in the field programmable gate array of the central logic board. Subsequently, a state machine formats the acquired data for its transmission to shore. We present the architecture and performance of the front-end firmware consisting of the TDCs and the state machine