Genetius

The study investigates the distinct roles of the two main chloroplastic ferredoxins, FDX1 and FDX2, in Chlamydomonas reinhardtii, showing that FDX1 is essential for growth and sulfur assimilation while FDX2 primarily supports nitrate/nitrite assimilation. Loss‑of‑function mutants revealed that FDX1 deficiency mimics sulfur deficiency at the transcriptomic level and reduces cellular sulfur, whereas FDX2 can partially compensate for sulfur metabolism when overexpressed.

The study identified two thylakoid lumenal TPM-domain proteins, LMTP1 and TLP26, in Chlamydomonas reinhardtii, produced knockout strains and recombinant proteins, and solved their crystal structures, revealing a novel redox‑responsive cysteine pair and manganese binding by LMTP1. Double mutants lacking both proteins exhibit impaired photosystem II acceptor‑side activity yet increased chlorophyll and photosynthetic protein synthesis, indicating that LMTP1 and TLP26 function redundantly in the maturation of nascent PSII complexes during assembly and repair.

The study characterizes the yellow‑in‑the‑dark (chIL) mutant of Chlamydomonas reinhardtii, revealing that loss of the CHLL subunit of dark‑operative POR prevents chlorophyll synthesis in the dark but allows rapid chloroplast biogenesis upon illumination, with pigment and photosynthetic protein accumulation within 1‑3 hours. Lincomycin treatment blocks plastid translation, halting light‑induced chloroplast development and cell growth, establishing the mutant and the drug as tools for dissecting chloroplast biogenesis and plastid‑to‑nucleus signaling.

Using CRISPR/Cas9 to delete the sole inner-envelope KEA homolog (CrKEA1) in Chlamydomonas reinhardtii, the authors showed that loss of this K/H antiporter impairs photoautotrophic growth, chloroplast morphology, and stromal rRNA maturation, mirroring phenotypes of Arabidopsis kea1kea2 mutants. Transcriptomic and single‑cell imaging analyses revealed both conserved responses (e.g., PhANG repression) and lineage‑specific effects (e.g., activation of the chloroplast unfolded protein response and defective cytokinesis). Heterologous expression of CrKEA1 rescued Arabidopsis kea1kea2 deficiencies, demonstrating functional continuity across green lineages.

The study investigates the role of the pyrenoid‑associated protein LCI9 in starch sheath formation in Chlamydomonas reinhardtii using an lci9 mutant. Loss of LCI9 disrupts sheath assembly, reduces inorganic carbon affinity, and impairs growth under low CO2, while proximity labeling reveals LCI9 is adjacent to starch‑metabolism enzymes and scaffolding proteins, and it also associates with starch in Arabidopsis.

The study examined nitrogen use strategies in the model alga Chlamydomonas reinhardtii by comparing growth on ammonium, nitrate, and urea, finding similar molar nitrogen utilization efficiency under saturating conditions. Rapid nitrogen uptake and storage were demonstrated through pulse experiments, and source‑specific transcriptome analysis revealed distinct regulation of assimilation pathways and transporters, supporting a model of flexible nitrogen acquisition and storage.

The authors introduced an enhancer-driven random gene overexpression (ERGO) screen in the green alga Chlamydomonas reinhardtii, generating >33,000 insertional mutants to identify genes affecting carotenoid metabolism. Visual screening revealed a mutant with elevated carotenoids and high‑light resistance, linked to upregulation of a novel F‑box protein gene (CMRP1), whose loss‑of‑function by CRISPR reduced carotenoid levels, confirming its regulatory role.

The study investigates how prior diurnal light acclimation influences fitness and the speed of photoprotective reprogramming in Chlamydomonas when light intensity shifts. HL‑acclimated cells show reduced growth and delayed cell‑cycle completion when moved to low light, whereas LL‑acclimated cells experience acute photodamage in high light but rapidly remodel thylakoid membranes, boost protective quenching, and restore chloroplast function within a single day. Transcriptomic and proteomic data reveal swift induction of thousands of genes, including those linked to the chloroplast unfolded protein response, underscoring the alga’s remarkable flexibility.

Using TurboID proximity labeling, the authors compared wild‑type CDJ5 with ATPase‑deficient and 4Fe‑4S‑cluster mutants in Chlamydomonas reinhardtii, revealing that the 4Fe‑4S cluster directs CDJ5 to a chloroplast microcompartment containing HSP70B, HSP90C, and PGRL1. The data suggest CDJ5, via its 4Fe‑4S cluster, cooperates with HSP70B/HSP90C to regulate photosynthetic electron flow and thylakoid membrane protein complex biogenesis.

The study demonstrates that Chlamydomonas reinhardtii elevates its intracellular zinc levels under low CO₂ conditions in a Cia5‑dependent manner, and reveals that Cia5 interacts constitutively with the metal‑binding GTPase ZNG3. While zng3 mutants retain most low‑CO₂ CCM gene induction, they fail to grow when excess carbon (high CO₂ or acetate) is supplied, suggesting ZNG3 and Cia5 jointly coordinate zinc trafficking and carbon metabolism.