Client distribution between Chlamydomonas FDX1 and FDX2 in carbon, nitrogen and sulfur assimilation
Year: 2026
Type: preprint
Abstract: ABSTRACT Plant-type ferredoxins (Fd) comprise small, soluble protein families that distribute electrons from photosystem I to various client proteins within the chloroplast stroma. In Chlamydomonas reinhardtii , the major, constitutively expressed FDX1/PetF supports Fd-NADP + reductase (FNR) in NADPH production. The highly similar FDX2 is present only when its preferred nitrogen (N) source ammonium is absent, supplying Fd-dependent nitrite reductase (NiR) for nitrate/nitrite assimilation. Surprisingly, despite accumulating to ∼10% of FDX1 abundance and preferential interaction with NiR, fdx2 mutants are asymptomatic when grown on nitrate, requiring to additionally deplete FDX1 for growth to be halted. A fdx1 knockout itself appears lethal, severe fdx1 knockdowns have reduced growth rates both in phototrophic and photoheterotrophic conditions, independent of the N source. Transcriptome analyses of fdx1 mutants revealed expression patterns similar to sulfur (S) deficient algae, and fdx1 strains have a reduced total cellular S content. S assimilation requires Fd-dependent sulfite reductase (SiR) activity, an enzyme distantly related to FDX2 client NiR. Expression defects are partially alleviated; growth and S content are less impacted with FDX2 expression. Our mutant analysis shows the two major Fds in Chlamydomonas focus on a specific subset of Fd-dependent metabolism, mostly supplying Fd-dependent enzymes involved in macronutrient assimilation (C/N/S).
Institution: Michigan State University
Language: English
Subfield: Molecular Biology
Domain: Life Sciences
SDG: Zero hunger
Open Access status: green
Awards: G1205207005, G222768804, Plant Biotechnology for Health and Sustainability, INTERDISCIPLINARY RESEARCH AND RELATED TRAINING PROGRAM IN THE PLANT SCIENCES, Plant Biotechnology for Health and Sustainability, G5648016710, G5922791890, INTERDISCIPLINARY RESEARCH AND RELATED TRAINING PROGRAM IN THE PLANT SCIENCES, G8850349022, INTERDISCIPLINARY RESEARCGH PROGRAM IN THE FUNDAMENTAL PLANT SCIENCES, G9000009466, G9000081629
OpenAlex ID: W7124423498