The Os-AKT1 Channel Is Critical for K+ Uptake in Rice Roots and Is Modulated by the Rice CBL1-CIPK23 Complex

Potassium (K + ) is one of the essential nutrient elements for plant growth and development. Plants absorb K + ions from the environment via root cell K + channels and/or transporters. In this study, the Shaker K + channel Os-AKT1 was characterized for its function in K + uptake in rice ( Oryza sativa ) roots, and its regulation by Os-CBL1 (Calcineurin B-Like protein1) and Os-CIPK23 (CBL-Interacting Protein Kinase23) was investigated. As an inward K + channel, Os-AKT1 could carry out K + uptake and rescue the low-K + -sensitive phenotype of Arabidopsis thaliana akt1 mutant plants. Rice Os- akt1 mutant plants showed decreased K + uptake and displayed an obvious low-K + -sensitive phenotype. Disruption of Os -AKT1 significantly reduced the K + content, which resulted in inhibition of plant growth and development. Similar to the AKT1 regulation in Arabidopsis , Os-CBL1 and Os-CIPK23 were identified as the upstream regulators of Os-AKT1 in rice. The Os-CBL1-Os-CIPK23 complex could enhance Os-AKT1-mediated K + uptake. A phenotype test confirmed that Os- CIPK23 RNAi lines exhibited similar K + -deficient symptoms as the Os- akt1 mutant under low K + conditions. These findings demonstrate that Os-AKT1-mediated K + uptake in rice roots is modulated by the Os-CBL1-Os-CIPK23 complex.