The calcium sensor PeCBL1, interacting with PeCIPK24/25 and PeCIPK26, regulates Na+/K+ homeostasis in Populus euphratica

This paper is the first to directly link two types of ion channel regulation pathway into an emerging and complex CBL-CIPK signal system in wooden plant. In Arabidopsis thaliana, the calcineurin b-like (CBL) 1 gene has been shown to be necessary in response to abiotic stresses. In this study, we identified CBL1 in the woody plant Populus euphratica, designated as PeCBL1. Heterologous expression of PeCBL1 could build the resistance of sensitive phenotypes to low K+ stress in the corresponding Arabidopsis cbl1/cbl9 mutant, and display a salt-sensitive phenotype compared with the mutant. Protein interaction analysis showed that PeCBL1 can interact with PeCIPK24, 25 and 26, and form different complexes of PeCBL-PeCIPK. To further investigate the mechanism of PeCBL1, we analyzed the fluxes of K+ and Na+ in roots of the wild-type Arabidopsis, cbl1/9 mutant, and PeCBL1 transgenic plants under low K+ stress and high Na+ stress. These analyses revealed that, compared to the cbl1/9 mutant, the PeCBL1 transgenic plant roots exhibited a higher capacity to absorb K+ after exposure to low K+ stress, and a lower capacity to discharge Na+ after exposure to salt stress. The results suggest that CBL1 interacts with CIPK24, CIPK25 and CIPK26 to regulate Na+/K+ homeostasis in Populus euphratica.