Potassium (K) is an essential nutrient, but levels of the free K ions (K+) in soil are often limiting, imposing a constant stress on plants. We have discovered a calcium (Ca2+)-dependent signalling network, consisting of two calcineurin B-like (CBL) Ca2+ sensors and a quartet of CBL-interacting protein kinases (CIPKs), which plays a key role in plant response to K+ starvation. The mutant plants lacking two CBLs (CBL2 and CBL3) were severely stunted under low-K conditions. Interestingly, the cbl2 cbl3 mutant was normal in K+ uptake but impaired in K+ remobilization from vacuoles. Four CIPKs-CIPK3, 9, 23 and 26-were identified as partners of CBL2 and CBL3 that together regulate K+ homeostasis through activating vacuolar K+ efflux to the cytoplasm. The vacuolar two-pore K+ (TPK) channels were directly activated by the vacuolar CBL-CIPK modules in a Ca2+-dependent manner, presenting a mechanism for the activation of vacuolar K+ remobilization that plays an important role in plant adaptation to K+ deficiency.

中文翻译：

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钙信号网络激活液泡 K+ 再动员，使植物适应低 K 环境。

钾 (K) 是一种必需营养素，但土壤中游离 K 离子 (K+) 的水平通常是有限的，对植物造成持续压力。我们发现了一个依赖钙 (Ca2+) 的信号网络，由两个钙调神经磷酸酶 B 样 (CBL) Ca2+ 传感器和一组 CBL 相互作用蛋白激酶 (CIPK) 组成，它在植物对 K+ 饥饿的反应中起关键作用。缺乏两个 CBL（CBL2 和 CBL3）的突变植物在低 K 条件下严重矮化。有趣的是，cbl2 cbl3 突变体在 K+ 吸收方面是正常的，但在 K+ 从液泡中的再动员方面受损。四个 CIPKs-CIPK3、9、23 和 26-被鉴定为 CBL2 和 CBL3 的伙伴，它们通过激活液泡 K+ 外流到细胞质来共同调节 K+ 稳态。