Biology subjects

Alric, J.

Publications and source records attributed to Alric, J..

6 recordsLinked to original sources

bioRxiv2025

Acclimation of photosynthesis began with a Cu-binding superoxide detoxifying enzyme

Plant acclimation is a growing scientific concept, at molecular, cellular and global scales. All photosynthetic organisms that created an oxic atmosphere on earth possess a gene of unknown function "Acclimation of Photosynthesis to the Environment 1". Here we show that APE1 encodes a thylakoid-bound protein with a unique motif that binds copper and detoxifies the superoxide anion radical, O2*-. Maturation of the recombinant APE1 protein from Chlamydomonas reinhardtii requires formation of cysteine disulfide bonds after copper binding or via a high affinity interaction with a copper chaperone (Plastid Copper Chaperone 1) that boosts its scavenging capacity for O2*-. APE1 co-occurs in evolution with Photosystem II oxygen evolving proteins and it is the archaic O2*- detoxifying enzyme for acclimating photosynthesis to an oxygenic environment.

plant biology↗

bioRxiv2024

Crystal structure of a Photosystem II-related, Manganese-binding, TPM-domain protein at a 1.6 A resolution

Many proteins conserved across oxygenic phototrophs play essential roles in photosynthetic function and acclimation, yet many remain unidentified or poorly characterized. In the green alga Chlamydomonas reinhardtii we identified two paralogous thylakoid lumenal proteins, encoded by Cre15.g636050 (LMTP1) and Cre03.g154600 (TLP26), belonging to the conserved TPM-domain (TLP18.3-Psb32-MOLO1) PF04536 family. We generated C. reinhardtii knock-out mutants for LMTP1 and TLP26 and produced recombinant proteins to assess their biochemical properties. The crystal structures of both proteins reveal the presence of a conserved redox-responsive cysteine pair, novel in TPM-domain proteins, and show that LMTP1 binds manganese. Double mutants lacking both LMTP1 and TLP26 show reduced photosynthetic performance due to effects at the acceptor-side of Photosystem II (PSII); however, these mutants accumulate more chlorophyll and photosynthetic proteins due to increased synthesis rates, a phenotype not observed for the single lmtp1 and tlp26 mutants. We propose that these two TPM-domain proteins, LMTP1 and TLP26, are functionally redundant in maturing nascent PSII intermediates during assembly and repair.

plant biology↗

bioRxiv2024

In vivo ElectroChromic Shift measurements of photosynthetic activity in far-red absorbing cyanobacteria

Some cyanobacteria can do photosynthesis using not only visible but also far-red light that is unused by most other oxygenic photoautotrophs because of its lower energy content. These species have a modified photosynthetic apparatus containing red-shifted pigments. The incorporation of red-shifted pigments decreases the photochemical efficiency of photosystem I and, especially, photosystem II, and it might affect the distribution of excitation energy between the two photosystems with possible consequences on the activity of the entire electron transport chain. To investigate the in vivo effects on photosynthetic activity of these pigment changes, we present here the adaptation of a spectroscopic method, based on a physical phenomenon called ElectroChromic Shift (ECS), to the far-red absorbing cyanobacteria Acaryochloris marina and Chroococcidiopsis thermalis PCC7203. ECS measures the electric field component of the trans-thylakoid proton motive force generated by photosynthetic electron transfer. We show that ECS can be used in these cyanobacteria to investigate in vivo the stoichiometry of photosystem I and photosystem II and their absorption cross-section, as well as the overall efficiency of light energy conversion into electron transport. Our results indicate that both species use visible and far-red light with similar efficiency, despite significant differences in their light absorption characteristics. ECS thus represents a new non-invasive tool to study the performance of naturally occurring far-red photosynthesis.

biophysics↗

bioRxiv2024

Redox regulation by the CDSP32 thioredoxin of ATP-synthase activity and enzymatic antioxidant network in Solanum tuberosum

Plant thioredoxins (TRXs) form a complex family involved in numerous metabolic and signalling pathways, such as the regulation of photosynthetic metabolism in relation with light conditions. The atypical CDSP32, chloroplastic drought-induced stress protein of 32 kDa, TRX includes two TRX-fold domains, one of which has an atypical redox-active HCGPC motif, and has been initially reported to participate in responses to oxidative stress as an electron donor to peroxiredoxins and methionine sulfoxide reductases. Here, we further characterized potato lines modified for CDSP32 expression to clarify the physiological roles of the TRX. Upon high salt treatments, modified lines displayed changes in the abundance and redox status of CDSP32 antioxidant partners, and exhibited sensitivity to NaHCO3, but not to NaCl. In non-stressed plants overexpressing CDSP32, a lower abundance of photosystem II PsbO and D1 subunits and ATP-synthase {gamma} subunit was noticed. The CDSP32 co-suppressed line showed altered chlorophyll a fluorescence induction and modified regulation of the plastidial ATP-synthase activity during dark/light and light/dark transitions, revealing the involvement of CDSP32 in the control of the photosynthetic machinery. In agreement with the previously reported interaction in planta between CDSP32 and the ATP-synthase {gamma} subunit, our data show that CDSP32 participates in the regulation of the transthylakoid membrane potential. Consistently, modeling of protein complex 3-D structure indicates that the CDSP32 TRX constitutes a suitable partner of ATP-synthase {gamma} subunit. We discuss the roles of CDSP32 in chloroplast redox homeostasis through the regulation of both photosynthetic activity and enzymatic antioxidant network.

plant biology↗

bioRxiv2023

The stromal side of cytochrome b6f complex regulates state transitions

In oxygenic photosynthesis, state transitions distribute light energy between Photosystem I and Photosystem II. This regulation involves the reduction of the plastoquinone pool, activation of the STT7 protein kinase by cytochrome b6f complex, phosphorylation and migration of Light Harvesting Complexes II (LHCII). Here we show the C-term of cyt b6 subunit acts on phosphorylation of STT7 and state transitions. We used site-directed mutagenesis of the chloroplast petB gene to truncate (remove L215b6) or elongate (add G216b6) the cyt b6 subunit. Modified complexes are devoid of heme ci and degraded by FTSH protease, revealing that salt bridge formation between cyt b6 (PetB) and subunit IV (PetD) is key to the assembly of the complex. In double mutants where FTSH is inactivated, modified cyt b6f are accumulated but the phosphorylation cascade is blocked. We also replaced the arginine interacting with heme ci propionate (R207Kb6). In this modified complex, heme ci is present but the kinetics of phosphorylation are slower. We show that highly phosphorylated forms of STT7 are accumulated transiently after reduction of the PQ pool, and represent the active forms of the protein kinase. 96% protein coverage using phosphoproteomics showed 4 new phosphorylated peptides in the kinase domain of STT7. Phosphorylation of the LHCII targets is favored at the expense of the protein kinase, and the migration of LHCII towards PSI is the limiting step for state transitions. Significance statementState transitions are regulatory mechanisms that optimize the quantum yield of photosynthesis. Chlamydomonas reinhardtii is the choice organism to study this regulation at the molecular level. Our study describes an unprecedented mechanism of stereochemical changes at the Qi site of the cytochrome b6f complex that trigger STT7 protein kinase activation through autophosphorylation.

plant biology↗

bioRxiv2020

ACCLIMATION OF PHOTOSYNTHESIS TO THE ENVIRONMENT 1 regulates Photosystem II Supercomplex dynamics in response to light in Chlamydomonas reinhardtii

Photosynthetic organisms require acclimation mechanisms to regulate photosynthesis in response to light conditions. Here, two mutant alleles of ACCLIMATION OF PHOTOSYNTHESIS TO THE ENVIRONMENT 1 (ape1) have been characterized in Chlamydomonas reinhardtii. The ape1 mutants are photosensitive and show PSII photoinhibition during high light acclimation or under high light stress. The ape1 mutants retain more PSII super-complexes and have changes to thylakoid stacking relative to control strains during photosynthetic growth at different light intensities. The APE1 protein is found in all oxygenic phototrophs and encodes a 25 kDa thylakoid protein that interacts with the Photosystem II core complex as monomers, dimers and supercomplexes. We propose a model where APE1 bound to PSII supercomplexes releases core complexes and promotes PSII heterogeneity influencing the stacking of Chlamydomonas thylakoids. APE1 is a regulator in light acclimation and its function is to reduce over-excitation of PSII centres and avoid PSII photoinhibition to increase the resilience of photosynthesis to high light.

plant biology↗