Dual-targeted NADK2 Links Mitochondrial Redox Homeostasis to Carbon Partitioning and Heterotrophic Growth in Chlamydomonas reinhardtii

Verdict. In Chlamydomonas reinhardtii , we localized CreNADK1 to the chloroplast, CreNADK3 to the cytoplasm, and CreNADK2 to both the chloroplast and mitochondria. It intersects mitochondrial stress/dysfunction themes (reactive oxygen species).

What the authors report

ABSTRACT NAD kinases (NADKs) can modulate NADP(H) levels across shifting environmental conditions.

Key results stated in the abstract include the following. In Chlamydomonas reinhardtii , we localized CreNADK1 to the chloroplast, CreNADK3 to the cytoplasm, and CreNADK2 to both the chloroplast and mitochondria. Importantly, during mixotrophic (light + acetate) and photoautotrophic (light) growth, most CreNADK2 is chloroplast localized whereas an increased proportion resides in mitochondria when the cells are grown heterotrophically (dark + acetate). In Cre nadk2 mutants, a diminished ability to synthesize mitochondrial NADP(H) inhibits the TCA cycle and markedly retards heterotrophic growth.

Why it matters for mitochondrial biology

Within mitochondrial research, this work maps primarily to redox biology, metabolism, immunology, genetics. It is relevant to mitochondrial dysfunction discourse because the abstract invokes reactive oxygen species. That does not by itself establish a validated disease mechanism; it indicates thematic proximity. Server: biorxiv. Posted 2026-08-17. Synthesis confidence is bounded by abstract completeness.

Study design (abstract-level)

The abstract does not cleanly separate methods from results. Treat design details as incomplete until the full preprint is inspected.

Principal findings

1. In Chlamydomonas reinhardtii , we localized CreNADK1 to the chloroplast, CreNADK3 to the cytoplasm, and CreNADK2 to both the chloroplast and mitochondria.
2. Importantly, during mixotrophic (light + acetate) and photoautotrophic (light) growth, most CreNADK2 is chloroplast localized whereas an increased proportion resides in mitochondria when the cells are grown heterotrophically (dark + acetate).
3. In Cre nadk2 mutants, a diminished ability to synthesize mitochondrial NADP(H) inhibits the TCA cycle and markedly retards heterotrophic growth.
4. In the light, photosynthesis becomes the primary energy source, and the presence of chloroplastic CreNADK1 enables near-normal growth in mutant cells, with inhibition of TCA cycle activity partially ameliorated via rerouting of acetate metabolism through the glyoxylate shunt, bypassing the TCA cycle and diminishing mitochondrial ROS production.
5. These findings demonstrate spatial plasticity of NAD(H)Ks and the implementation of ‘bypass’ metabolism to enable growth of Cre nadk2 mutants.

Limitations of this brief

• This Mitos brief is an abstract-level synthesis of a preprint; it is not peer review and not a substitute for reading the full paper.
• Preprint status: findings may change with revision or journal review.
• Effect sizes, n numbers, statistics, and full experimental controls are typically incomplete at abstract resolution.
• Comparator/control language is weak or absent in the abstract, limiting causal inference from this brief alone.
• Primary source: biorxiv DOI 10.64898/2026.08.14.744979 (posted 2026-08-17).

Open scientific questions

• Which specific experimental panels in the full paper establish the strongest causal claim, and how robust are the controls?
• How do these findings sit relative to prior literature on the same pathway—replication, contradiction, or incremental extension?

Bottom line

For mitochondrial biologists focused on redox biology, metabolism, immunology, this preprint is worth full-text review if the topic matches your program. Abstract-level takeaway: In Chlamydomonas reinhardtii , we localized CreNADK1 to the chloroplast, CreNADK3 to the cytoplasm, and CreNADK2 to both the chloroplast and mitochondria. Confirm methods, effect sizes, and controls in the full PDF before citing the result as established.

Bibliographic record

Abstract-based editorial synthesis by Mitos. Not peer review.