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International audience; NFU3 is one of the two NFU proteins present in the chloroplast of Chlamydomonas involved in the insertion of (iron-sulfur) Fe-S clusters in client proteins. Fe-S proteins are found in several chloroplastic processes such as photosynthesis, chlorophyll, amino acid and sulfur metabolisms (see abstract Przybyla-Toscano et al. for more information). Three insertional mutants of the CLIP library [1] bearing a disruption of the NFU3 gene are analyzed. Growth of the mutants is affected in the light and to a lesser extent in the dark when cells are grown on acetate. The maximum photosynthesis efficiency and PSII are slightly reduced. No major decrease of proteins constituting the core of Photosystem I is observed by Western blotting. Chlorophyll metabolism is investigated. Two Fe-S enzymes are affected in the nfu3 mutants: the dark-operative Fe-S protochlorophyllide oxidoreductase (DPOR) and the 7 hydroxy-methyl chlorophyll a reductase (HCAR). DPOR is an enzyme catalyzing the synthesis of chlorophyll in the dark, which is present in algae, but lost in angiosperms. HCAR plays a critical role in chlorophyll degradation, when cells are starved of nitrogen [2]. To find additional targets, the promoter sequence of NFU3 was scanned for putative cis-regulatory elements. Motifs for anaerobiosis and sulfur-deprivation are present. Fe-S enzymes of the fermentative metabolism are currently investigated. First results show that the pyruvate ferredoxin oxidoreductase and H2 metabolism would be impacted. Binary yeast two-hybrid experiments aiming at validating the interactions of NFU3 with the candidate client Fe-S proteins are underway (see abstract Przybyla-Toscano et al.). Additional targets present in the sulfur or amino acid metabolism will be investigated. Overall, our results suggest that NFU3 is involved in maturation of both classical and algal-specific Fe-S enzymes, which could be relevant biotechnological applications.Funded by FNRS-FWO EOS Project 30829584 and CDR J.0175.20[1] X. Li et al. Nature Genetics 51, 627 (2019).[2] S. Schmollinger et al. Plant Cell 26, 410 (2014).

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

An Arabidopsis homolog of the mammalian mitochondrial calcium uniporter MCU acts as Ca2+ channel, and its absence impacts mitochondrial function and morphology.

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• –) ≥ 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 μM, 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 μM), prevents H2O2 accumulation under high-light illumination conditions, thus providing antioxidant surveillance and photoprotection.