Biology subjects

Choquet, Y.

Publications and source records attributed to Choquet, Y..

5 recordsLinked to original sources

bioRxiv2025

The first photosynthetic mutant in diatoms targets the subunit γ of plastidial ATP synthase and reveals a key role of thylakoid electrochemical proton gradient in photosynthesis regulation and heterotrophic metabolism.

Diatoms are major phytoplanktonic algae with secondary endosymbiotic plastids that differ in cellular and regulatory traits from those of the green lineage. Here we exploited the heterotrophic growth ability of Cyclotella cryptica to create the first diatom photosynthetic mutant by CRISPR-Cas inactivation of the nucleus-encoded ATP synthase subunit {gamma}. These mutants showed impaired phototrophic capacity and altered thylakoids morphology. In absence of {gamma}-ATP, protons that accumulate in the thylakoid lumen slow down the cytochrome b6f complex, thus keeping the electron carriers downhill oxidized. These results, reversible when the proton gradient is suppressed, demonstrate the existence of a photosynthetic control in diatoms. At variance with the wild type, {gamma} ATP synthase mutants cannot grow heterotrophically in darkness nor in the light when photosystem II is inhibited. This requirement of heterotrophic growth on photosynthetic electron transfer or on the presence of plastidial ATP synthase suggests that the proton motive force (pmf) is a central integrator of the metabolic interaction between photosynthesis and heterotrophy. Our results establish C. crytica as a robust model for analysis of photosynthetic function, regulation and metabolic integration in organisms with secondary plastids. TeaserMutagenesis in the facultative autotroph diatom Cyclotella cryptica enables exploration of essential plastid functions in diatoms

plant biology↗

bioRxiv2024

Complexome profiling of the Chlamydomonas psb28 mutant reveals THYLAKOID ENRICHED FRACTION 5 as an early photosystem II assembly factor

Several auxiliary factors are required for the assembly of photosystem (PS) II, one of which is Psb28. While the absence of Psb28 in cyanobacteria has little effect on PSII assembly, we show here that the Chlamydomonas psb28-null mutant is severely impaired in PSII assembly, showing drastically reduced PSII supercomplexes, dimers and monomers, while overaccumulating RCII, CP43mod and D1mod. The mutant had less PSI and more Cytb6f and showed fewer thylakoid stacks and distorted chloroplast morphology. Complexome profiling of the psb28 mutant revealed that TEF5, the homolog of Arabidopsis PSB33/LIL8, co-migrated particularly with RCII. TEF5 also interacted with PSI. A Chlamydomonas tef5 null mutant is also severely impaired in PSII assembly and overaccumulates RCII and CP43mod. RC47 was not detectable in the light-grown tef5 mutant. Our data suggest a possible role for TEF5 in facilitating the assembly of CP47mod into RCII. Both the psb28 and tef5 mutants exhibited decreased synthesis of CP47 and PsbH, suggesting negative feedback regulation possibly exerted by the accumulation of RCII and/or CP43mod in both mutants. The strong effects of missing auxiliary factors on PSII assembly in Chlamydomonas suggest a more effective protein quality control system in this alga than in land plants and cyanobacteria. One-sentence summaryThe Chlamydomonas psb28 mutant is severely impaired in PSII assembly which via complexome profiling allowed identifying TEF5 as a novel PSII assembly factor that likely facilitates CP47 assembly. The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (https://academic.oup.com/plcell/pages/General-Instructions) is: Michael Schroda (m.schroda@rptu.de).

plant biology↗

bioRxiv2021

Retracing the evolution from antimicrobial to targeting peptides

We asked what peptide features govern targeting to the mitochondria versus the chloroplast using antimicrobial peptides as a starting point. This approach was inspired by the endosymbiotic hypothesis that organelle-targeting peptides derive from antimicrobial amphipathic peptides delivered by the host cell, to which organelle progenitors became resistant. To explore the molecular changes required to convert antimicrobial into targeting peptides, we expressed a set of 13 antimicrobial peptides in Chlamydomonas reinhardtii. Peptides were systematically modified to test distinctive features of mitochondrial and chloroplast targeting peptides, and we assessed their targeting potential by following the intracellular localization and maturation of a Venus fluorescent reporter used as cargo protein. Mitochondrial targeting can be achieved by some unmodified antimicrobial peptide sequences. Targeting to both organelles is improved by replacing Lysines with Arginines. Chloroplast targeting is enabled by the presence of flanking unstructured sequences, additional constraints consistent with chloroplast endosymbiosis having occurred in a cell that already contained mitochondria. If indeed targeting peptides evolved from antimicrobial peptides, required modifications imply a temporal evolutionary scenario with an early exchange of cationic residues, and a late acquisition of chloroplast specific motifs.

evolutionary biology↗

bioRxiv2021

Complexome profiling on the lpa2 mutant reveals insights into PSII biogenesis and new PSII associated proteins

We have identified the homolog of LOW PSII ACCUMULATION 2 (LPA2) in Chlamydomonas. A Chlamydomonas lpa2 mutant grew slower in low light and was hypersensitive to high light. PSII maximum quantum efficiency was reduced by 38%. Synthesis and stability of newly made PSII core subunits D1, D2, CP43, and CP47 were not impaired. Complexome profiling revealed that in the mutant CP43 was reduced to [~]23%, D1, D2, and CP47 to [~]30% of wild-type levels, while small PSII core subunits and components of the oxygen evolving complex were reduced at most by factor two. PSII supercomplexes, dimers, and monomers were reduced to 7%, 26%, and 60% of wild-type levels, while RC47 was increased [~]6-fold. Our data indicate that LPA2 acts at a step during PSII assembly without which PSII monomers and especially further assemblies become intrinsically unstable and prone to degradation. Levels of ATP synthase and LHCII were 29% and 27% higher in the mutant than in the wild type, whereas levels of the cytochrome b6f complex were unaltered. While the abundance of PSI core subunits and antennae hardly changed, LHCI antennae were more disconnected in the lpa2 mutant, presumably as an adaptive response to reduce excitation of PSI. The disconnection of LHCA2,9 together with PSAH and PSAG was the prime response, but independent and additional disconnection of LHCA1,3-8 along with PSAK occurred as well. Finally, based on co-migration profiles, we identified three novel putative PSII associated proteins with potential roles in regulating PSII complex dynamics, assembly, and chlorophyll breakdown. One-sentence summaryWe provide evidence that the Chlamydomonas LPA2 homolog acts at a step in PSII biogenesis without which PSII monomers and further assemblies become unstable and prone to degradation.

plant biology↗

bioRxiv2020

An antimicrobial origin of targeting peptides to endosymbiotic organelles

Mitochondria and chloroplasts emerged from primary endosymbiosis. Most proteins of the endosymbiont were subsequently expressed in the nucleo-cytosol of the host and organelle-targeted via the acquisition of N-terminal presequences, whose evolutionary origin remains enigmatic. Using a quantitative assessment of their physico-chemical properties, we show that organelle targeting peptides, which are distinct from signal peptides targeting other subcellular compartments, group with a subset of antimicrobial peptides. We demonstrate that extant antimicrobial peptides target a fluorescent reporter to either the mitochondria or the chloroplast in the green alga Chlamydomonas reinhardtii and, conversely, that extant targeting peptides still display antimicrobial activity. Thus, we provide strong computational and functional evidence for an evolutionary link between organelle-targeting and antimicrobial peptides. Our results support the view that resistance of bacterial progenitors of organelles to the attack of host antimicrobial peptides has been instrumental in eukaryogenesis and in emergence of photosynthetic eukaryotes.

evolutionary biology↗