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Potassium (K+) deficiency severely threatens crop growth and productivity. Calcium (Ca2+) signaling and its sensors play a central role in the response to low-K+ stress. Calmodulin (CaM) is an important Ca2+ sensor. However, the mechanism by which Ca2+ signaling and CaM mediate the response of roots to low-K+ stress remains unclear. In this study, we found that the K+ concentration significantly decreased in both shoots and roots treated with Ca2+ channel blockers, a Ca2+ chelator, and CaM antagonists. Under low-K+ stress, reactive oxygen species (ROS) accumulated, and the activity of antioxidant enzymes, NAD kinase (NADK), and NADP phosphatase (NADPase) decreased. This indicates that antioxidant enzymes, NADK, and NADPase might be downstream target proteins in the Ca2+-CaM signaling pathway, which facilitates K+ uptake in plant roots by mediating ROS homeostasis under low-K+ stress. Moreover, the expression of NtCNGC3 , NtCNGC10 , K+ channel genes, and transporter genes was significantly downregulated in blocker-treated, chelator-treated, and antagonist-treated plant roots in the low K+ treatment, suggesting that the Ca2+-CaM signaling pathway may mediate K+ uptake by regulating the expression of these genes. Overall, this study shows that the Ca2+-CaM signaling pathway promotes K+ absorption by regulating ROS homeostasis and the expression of K+ uptake-related genes in plant roots under low-K+ stress. [ABSTRACT FROM AUTHOR]

Potassium (K + ) deficiency severely threatens crop growth and productivity. Calcium (Ca 2+ ) signaling and its sensors play a central role in the response to low-K + stress. Calmodulin (CaM) is an important Ca 2+ sensor. However, the mechanism by which Ca 2+ signaling and CaM mediate the response of roots to low-K + stress remains unclear. In this study, we found that the K + concentration significantly decreased in both shoots and roots treated with Ca 2+ channel blockers, a Ca 2+ chelator, and CaM antagonists. Under low-K + stress, reactive oxygen species (ROS) accumulated, and the activity of antioxidant enzymes, NAD kinase (NADK), and NADP phosphatase (NADPase) decreased. This indicates that antioxidant enzymes, NADK, and NADPase might be downstream target proteins in the Ca 2+ -CaM signaling pathway, which facilitates K + uptake in plant roots by mediating ROS homeostasis under low-K + stress. Moreover, the expression of NtCNGC3 , NtCNGC10 , K + channel genes, and transporter genes was significantly downregulated in blocker-treated, chelator-treated, and antagonist-treated plant roots in the low K + treatment, suggesting that the Ca 2+ -CaM signaling pathway may mediate K + uptake by regulating the expression of these genes. Overall, this study shows that the Ca 2+ -CaM signaling pathway promotes K + absorption by regulating ROS homeostasis and the expression of K + uptake-related genes in plant roots under low-K + stress., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Wang, Dai, Xu, Dai, Chen, Zhang and Zhang.)