Biology subjects

Cardol, P.

Publications and source records attributed to Cardol, P..

4 recordsLinked to original sources

bioRxiv2026

Structural basis for far-red light harvesting in a euglenophyte photosystem II supercomplex

Photosystem II (PSII) is in eukaryotic phototrophs is generally considered to operate within a more restricted spectral range than photosystem I (PSI), in which long-wavelength chlorophylls are a well-established feature of the peripheral antenna. Whether eukaryotic PSII can acquire comparable far-red-associated properties through lineage-specific antenna diversification has remained unclear. Here we present a 3.09 [A] cryo-electron microscopy structure of the C2S2M2L2 PSII supercomplex from Euglena gracilis, a euglenophyte species harbouring a secondary plastid and unusual light-harvesting system. We show that the euglenophyte-specific antenna protein LhcE9 occupies the position corresponding to canonical Lhcb5, but in a markedly different orientation that creates a distinct interface with the PSII core, particularly with CP43. Combined structural, spectroscopic, mutagenesis and proteomic analyses support LhcE9 as the stably bound PSII antenna subunit most closely associated with the far-red state in the supercomplex. Excitation-energy-transfer calculations further indicate two fast lineage-specific antenna-to-core routes mediated by LhcE9 and PsbX. Together, these findings reveal an unexpected mode of PSII antenna diversification and provide a structural framework for far-red-associated light harvesting in PSII.

plant biology↗

bioRxiv2026

Proteomic Response of Thalassiosira pseudonana to Anoxia Reveals Alanine Fermentation Pathway and Reprogramming of Nitrogen Metabolism

O_LIDiatoms are key players in marine ecosystems and are frequently exposed to low-oxygen conditions in sediments and oxygen minimum zones. However, the metabolic strategies that enable their survival under anoxia remain poorly understood. C_LIO_LIUsing the model diatom Thalassiosira pseudonana, we investigated its response to dark anoxia. We first used proteomic approaches to identify differences between dark anoxia and dark oxic conditions combined with a phylogenetic analysis to decipher how the anoxic tolerance was acquired by this lineage. This approach revealed unexpected shunts involving amino acid pathways. We then correlated these findings with targeted metabolomic analysis on amino acids. C_LIO_LIOur results show that the diatom T. pseudonana undergoes a coordinated metabolic reprogramming under anoxia, centered on alanine production and tightly coupled to nitrogen metabolism. This work reveals how carbon and nitrogen fluxes are integrated to maintain cellular homeostasis in the absence of oxygen and provides a framework for understanding the resilience of diatoms in oxygen-depleted environments. C_LIO_LIWe identify three key features for anoxic adaptation in this lineage (i) alanine-centered metabolic reprogramming as a central component of acclimation to anoxia (ii) the involvement of an arginine-succinate shunt; and (iii) a critical contribution of lateral gene transfer (LGT) for anoxic tolerance. C_LI

plant biology↗

bioRxiv2025

A Unique LHCE Light-Harvesting protein Family is involved in Photosystem I and II Far-Red Absorption in Euglena gracilis

Photosynthetic organisms have evolved diverse strategies to adapt to fluctuating light conditions, balancing efficient light capture with photoprotection. In green algae and land plants, this involves specialized light-harvesting complexes (LHCs), non-photochemical quenching, and state transitions driven by dynamic remodeling of antenna proteins associated with Photosystems (PS) I and II. Euglena gracilis, a flagellate with a secondary green plastid, represents a distantly related lineage whose light-harvesting regulation remains poorly understood. Although spectral shifts under different light regimes have been observed, their molecular basis was unknown. Here, through integrated phylogenomic, proteomic, structural, and spectroscopic analyses, we identify a novel chlorophyll a far-red-absorbing antenna complex in E. gracilis, composed of a species-specific Lhce protein family. This antenna forms a pentameric complex under low light and transiently associates with PSII during far-red light exposure. It is structurally and functionally distinct from canonical LHCII{square} trimers and absent in Viridiplantae. Additionally, PSI in E. gracilis is surrounded by an expanded Lhce/LhcbM belt around a minimal core. These findings reveal a unique mechanism for regulating PS antenna size in E. gracilis, distinct from known models in plants and green algae, and highlight an alternative evolutionary strategy for light acclimation in organisms with secondary plastids. HighlightEuglena gracilis features a unique, lineage-specific LhcE antenna system that dynamically associates with PSII and expands PSI light harvesting, revealing an alternative strategy for light acclimation in secondary plastids.

plant biology↗

bioRxiv2017

Cyclic electron flow in Chlamydomonas reinhardtii

Cyclic electron flow (CEF), one of the major alternative electron transport pathways to the primary linear electron flow (LEF) in chloroplasts has been discovered in the middle of the last century. It is defined as a return of the reductants from the acceptor side of the Photosystem I (PSI) to the pool of its donors via the cytochrome b6f, and has proven essential for photosynthesis. However, despite many efforts aimed at its characterisation, the pathway and regulation of CEF remain equivocal, and its physiological significance remains to be properly defined. Here we use novel spectroscopic approaches to measure CEF in transitory conditions in the green alga Chlamydomonas reinhardtii. We show that CEF operates at the same maximal rate regardless of the oxygen concentration, and that the latter influences LEF, rather than CEF in vivo, which questions the recent hypotheses about the CEF supercomplex formation. We further reveal that the pathways proposed for CEF in the literature are inconsistent with the kinetic information provided by our measurements. We finally provide cues on the regulation of CEF by light.

plant biology↗