Genetius

The study identifies APE1 as a thylakoid-associated protein that binds copper and detoxifies superoxide radicals, providing a mechanism for photosynthetic acclimation to oxygenic conditions. Recombinant APE1 from Chlamydomonas reinhardtii matures through cysteine disulfide bond formation after copper binding or via interaction with Plastid Copper Chaperone 1, enhancing its O2*‑ scavenging capacity.

The study identifies a nuclear protein, CBP1, that represses the CO2‑concentrating mechanism (CCM) in the green alga Chlamydomonas reinhardtii when CO2 is abundant. Using pull‑down screens and CRISPR/Cas9 knockouts, the authors show that loss of CBP1 derepresses CCM genes and enhances carbonic anhydrase and transporter expression, increasing inorganic carbon affinity under high CO2, a phenotype rescued by complementation or acetazolamide treatment. These findings reveal a zinc‑dependent regulatory “off switch” that balances energy expenditure and carbon capture in algae.

The study examined how Chlamydomonas reinhardtii adjusts its metabolism under fluctuating light (FL) compared with constant high or low light, across high and low CO2 conditions. Proteomic and metabolomic analyses revealed that low CO2 drives a carbon‑concentrating mechanism and photorespiration, while high CO2 supports growth by increasing ATP pools and promoting mitochondrial respiration, cyclic electron flow, and starch turnover. The results highlight a CO2‑dependent energy trade‑off between photoprotection, repair, and carbon allocation that governs growth under FL.

The study demonstrates that in the green alga Chlamydomonas reinhardtii, distinct photosynthetic electron flow pathways each operate efficiently over specific light‑fluctuation frequencies, defined as their bandwidths. By systematically varying light periodicities, the authors show that cyclic electron flow handles a broad range, pseudo‑cyclic electron flow supports rapid fluctuations, and chloroplast‑mitochondria electron flow is limited to slower changes, linking these capacities to ATP generation and photoprotection. The findings suggest that cells dynamically adjust the contribution of each pathway according to the frequency of environmental light changes.

The study examines how a multifactorial stress combination (MFSC) of five abiotic stresses affects wild‑type and rbo1 mutant Chlamydomonas reinhardtii cells, revealing that MFCS induces cell aggregation, especially in the rbo1 mutant, and that H2O2 can trigger this response. Proteomic profiling shows physiological changes accompanying aggregation, suggesting that stress‑induced aggregation may have broader ecological impacts and could have been a driver for early multicellularity.

The study introduced a cyanobacterial dual-function FBP/SBPase into Chlamydomonas reinhardtii, confirming its Mg2+-dependent catalytic activity and enhanced photosynthetic performance while reducing singlet‑oxygen formation under high light. Although increased cell size was observed across conditions, notable growth and biomass gains—including starch, protein, and lipid accumulation—occurred only under mixotrophic, light‑ and CO2‑limited conditions, also improving sedimentation for harvesting.

The study examined how phosphorylation of plastocyanin (PC) influences its interactions with cytochrome‑b6f (Cytb6f) and Photosystem I (PSI) in Chlamydomonas reinhardtii, identifying two binding orientations (Side‑on and Head‑on) via cross‑linking mass spectrometry. A phosphomimetic PC variant accelerated Cytb6f oxidation but slowed electron transfer to PSI, indicating that PC phosphorylation fine‑tunes electron flow under high‑light stress.

The study uncovers a feedback mechanism wherein phosphomimic mutation (PetD T4E) or deletion of the N‑terminal five amino acids of the b6f subunit PetD suppresses STT7 kinase activity, leading to a State 1‑locked phenotype and impaired electron transfer, highlighting the essential regulatory role of the PetD N‑terminus in photosynthetic state transitions.

A forward genetic screen in Chlamydomonas identified a mutant lacking PSII activity due to disruption of the CrHCF244 gene, the algal homolog of Arabidopsis HCF244, which is required for translation of the chloroplast psbA mRNA encoding the D1 protein. Arabidopsis HCF244 partially rescued the mutant, demonstrating functional conservation, while a high frequency of suppressor mutants suggests additional factors can regulate psbA translation.