2025-11-25 中国科学院(CAS)
中国科学院武漢植物園の研究によって、水生植物 Ottelia alismoides が通常は同一細胞で共存しない C4光合成(NAD-ME型)・CAM・HCO₃⁻利用という3種類のCO₂濃縮機構(CCMs)を同時に作動させる極めて特異な植物であることが示された。研究チームは高低CO₂条件下での栽培に加え、酵素活性測定、細胞内局在、トランスクリプトーム、プロテオーム、¹³C標識を組み合わせ、単一細胞内での3つのCCMの協調機構を解析した。O. alismoides は一般的C4植物と異なり、初期固定産物としてマレートを用い、夜間には特定PEPCとMDH1がCAMサイクルを担い、日中には別のアイソフォームがC4代謝を駆動する。さらに輸送体TDT・DTCが両経路のマレート輸送を調整し、NAD-MEでの脱炭酸を通じてカルビン回路にCO₂を供給する仕組みが明らかになった。
Coordinated metabolic model of HCO₃⁻ utilization, C₄ and CAM pathways in Ottelia alismoides. (Image by WBG)
<関連情報>
- https://english.cas.cn/newsroom/research_news/life/202511/t20251125_1133183.shtml
- https://nph.onlinelibrary.wiley.com/doi/10.1111/nph.70673
水生植物におけるCAMと重炭酸塩の利用を統合した新規単細胞NAD-ME C4サブタイプ A novel single-cell NAD-ME C4 subtype integrated with CAM and bicarbonate use in an aquatic plant
Hong Sheng Jiang, Wenmin Huang, Shijuan Han, Pengpeng Li, Zuying Liao, Liyuan Wei, Lei Zhao, Shuping Gu, Jun Ding, Brigitte Gontero, Stephen C. Maberly, Wei Li
New Phytologist Published: 21 October 2025
DOI:https://doi.org/10.1111/nph.70673
Summary
- Many plants maximize photosynthesis by using a CO2-concentrating mechanism (CCM). Based on physiology, the freshwater plant Ottelia alismoides has three CCMs: C4 metabolism (NAD-malic enzyme (NAD-ME) subtype) and bicarbonate-use during the day plus crassulacean acid metabolism (CAM) at night and lacks Kranz anatomy.
- Here, we combined a range of techniques including analysis of enzyme activity and location, transcriptomics, proteomics and 13C labelling in plants grown at low and high concentrations of CO2 to investigate how these CCMs interact and can be integrated without Kranz anatomy.
- We showed that, unlike canonical NAD-ME subtypes, malate is the first stable compound, produced by a cytosolic malate dehydrogenase, rather than aspartate produced by aspartate aminotransferase. CAM depends on the nocturnal synthesis and transport of malic acid into the vacuole involving a vacuolar-ATPase and a tonoplast dicarboxylate transporter that are highly expressed at night.
- These results show that C4 and CAM are compatible within a single cell, thanks to temporal regulation and expression of different isoforms of key enzymes and transporters. They contribute to the growing appreciation of the diversity of CCMs and how different processes can co-occur and be coordinated. This study presents a model that could facilitate future plant engineering.
