Carbon dioxide not only plays a central role in the carbon cycle, but also acts as a crucial signal in living cells. Adaptation to changing CO₂ concentrations is critical for all organisms. Conversion of CO₂ to HCO₃⁻ by carbonic anhydrase and subsequent HCO₃⁻-triggered signalling are thought to be important for cellular responses to CO₂ (refs. ^1,2,3). However, carbonic anhydrases are suggested to transduce a change in CO₂ rather than be a direct CO₂ sensor^4,5, the mechanism(s) by which organisms sense CO₂ remain unknown. Here we demonstrate that a unique group of PP2C phosphatases from fungi and plants senses CO₂, but not HCO₃⁻, to control diverse cellular programmes. Different from other phosphatases, these PP2Cs all have an intrinsically disordered region (IDR). They formed reversible liquid-like droplets through phase separation both in cells and in vitro, and were activated in response to elevated environmental CO₂ in an IDR-dependent manner. The IDRs in PP2Cs are characterized by a sequence of polar amino acids enriched in serine/threonine, which provides CO₂ responsiveness. CO₂-responsive activation of PP2Cs via the serine/threonine-rich IDR-mediated phase separation represents a direct CO₂ sensing mechanism and is widely exploited.

二氧化碳不仅在碳循环中起着核心作用，而且在活细胞中也起着至关重要的作用。适应不断变化的 CO ₂浓度对所有生物都至关重要。通过碳酸酐酶将CO ₂转化为HCO ₃ ^-和随后的HCO ₃ ^-触发信号被认为对于细胞对CO ₂的反应很重要（参考文献^1,2,3）。然而，建议碳酸酐酶转导 CO 2 的变化，_而不是直接的 CO ₂传感器^4,5，这是生物体感知 CO _2的机制仍然未知。在这里，我们证明了来自真菌和植物的一组独特的 PP2C 磷酸酶可以感知 CO ₂，​​但不感知 HCO ₃ ^-，以控制不同的细胞程序。与其他磷酸酶不同，这些 PP2Cs 都具有内在无序区域 (IDR)。它们在细胞和体外通过相分离形成可逆的液体状液滴，并以 IDR 依赖性方式响应升高的环境 CO _{2被激活。}PP2Cs 中的 IDR 以富含丝氨酸/苏氨酸的极性氨基酸序列为特征，提供 CO ₂响应性。通过富含丝氨酸/苏氨酸的 IDR 介导的相分离对 PP2C 的CO _{2响应性激活代表了直接的 CO2}传感机制，并被广泛利用。