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.
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We thank the Arabidopsis Biological Resource Center for providing Arabidopsis thaliana seed stocks. This work was supported by the National Science Foundation (grant nos. MCB-1714795 and ISO-1339239 to S.L.), the Innovative Genomics Institute of the University of California (to S.L.) and the National Natural Science Foundation of China (grant no. 31770266 to F.-G.Z.). C.W. is sponsored by the Tang Distinguished Scholarship of the University of California at Berkeley.
The authors declare no competing interests.
Peer review information Nature Plants thanks Ingo Dreyer, Enrico Martinoia and the other, anonymous, reviewer for their contribution to the peer review of this work.
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Tang, RJ., Zhao, FG., Yang, Y. et al. A calcium signalling network activates vacuolar K+ remobilization to enable plant adaptation to low-K environments. Nat. Plants 6, 384–393 (2020). https://doi.org/10.1038/s41477-020-0621-7
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