Functional Analysis Of Potassium Channel OsAKT1and Its Regulators In Rice K~+Uptake

Potassium (K+) is the most abundant monovalent cation in plant cells, and plays crucial roles in plant growth and development. Potassium in plants is mainly absorbed from soil, which is mediated by K+channels and K+transporters. In the model plant Arabidopsis, K+channel AKT1is identified as the important component involving in root K+uptake, whose activity is modulated by many different regulators. For the crops, some K+channels and K transporters were also cloned, however, their physiological functions in crops are still unclear. In this dissertation work, we analyzed the physiological function of K+channel OsAKT1in rice. In addition, the regulators of OsAKT1were screened, whose physiological functions were also verified in rice.Rice OsAKT1is the homolog of Shaker potassium channel AKT1from Arabidopsis. The amino acid sequence analysis showed that OsAKT1and AKT1are highly conserved, which indicated their similar physiological functions in plants. OsAKT1could complement the growth of yeast K+defect mutant strain R5421suggesting the K+transport activity of OsAKT1.In addition, OsAKT1could rescue the low-K+-sensitive phenotype of Arabidopsis aktl mutant. The phenotype analysis showed that the rice osaktl mutant plants displayed the obvious low-K+-sensitive phenotype compared with the wild-type rice plants. The osaktl mutant showed growth inhibition, leaf brown spots and reduction of K1content. The results of K--depletion experiments showed that the K+uptake rate in osaktl mutant plants was obviously slower than that in wild-type plants. These results demonstrated that the loss-of-function of OsAKT1led to the reduction of K+uptake in osaktl mutant, which caused the growth inhibition and K+-deficient symptom in mutant plants. Furthermore, the growth of osaktl mutant plants was inhibited during the whole development stages. The heading and grain-filling stages were delayed in osaktl mutant, and the grain yield was also impaired. These data demonstrate that the K+channel OsAKT1plays a crucial role in rice root K+uptake.Furthermore, we tried to screen the regulators of OsAKT1and verified the physiological functions of these regulators. According to the investigation of AKT1in Arabidopsis, the rice calcium sensor OsCBLl and protein kinase OsCIPK23are proposed as the regulators of OsAKT1. OsCBL1and OsCIPK23were both expressed in rice roots, and especially OsCIPK23could be induced by low-K+treatment. Yeast two-hybrid results showed that OsCIPK23could interact with OsAKT1as well as OsCBL1. Phenotype analysis indicated that OsCIPK23and OsCBL1could rescue the low-K’-sensitive phenotype of Arabidopsis Iksl (cipk23) and cbll cbl9mutants, respectively. Moreover, OsCIPK23RNAi rice plants displayed the similar low-K+-sensitive phenotype as osaktl mutant. These results indicated that OsAKT1-mediated K+uptake in rice roots is modulated by OsCBLl-OsCIPK23complex.All the data in this dissertation demonstrate that K+channel OsAKT1is an important component mediated K+uptake in rice roots. The activity of OsAKT1is regulated by the calcium sensor OsCBLl and protein kinase OsCIPK23. These results will provide the theoretical basis that would be used to improve the rice K+utilization efficiency via molecular biology methods.