Functional Analyses Of ZmCBL-ZmCIPK In Potassium Uptake And Translocation In Zea Mays

Potassium(K)is one of the essential macronutrients for plant growth and development.In China,K deficiency has become a limited factor for crop production,Genetic improvement of crop K acquisition and utilization efficiency(KUE)is considered as one of approaches to solve this problem.Previous study has revealed a regulatory pathway for K~+ uptake in Arabidopsis.The K~+ channel AKT1 mediates K~+ uptake in Arabidopsis root,and AKT1 activity is regulated by the Ca2+ binding protein CBL1/9 and protein kinase CIPK23.Overexpression of CBL1/9 and CIPK23 can enhance Arabidopsis tolerance to low-K~+ stress by increasing K~+ uptake.ZMK1 is the homolog of AKT1 in maize,whose activity could be activated by ZmCBL1 and several ZmCIPK proteins in vitro.In this dissertation work,the physiological functions of ZmCBL1 and ZmCIPK3/9/23 in maize K~+ uptake and translocation were analyzed.The ZmCBL1 and ZmCIPK3/9/23 overexpressing(OE)maize plants were generated and the KUE of these transgenic inbred maize lines were determined.The hydroponic culture experiments indicated that ZmCBL1 OE lines were sensitive to low-K~+ stress,whose older leaves showed chlorosis symptom.The K~+ content in both root and shoot of ZmCBL1 OE plants were lower than that of control plants under low-K~+ conditions.These results indicated that overexpression of ZmCBLl may lead to a sensitive phenotype of maize to low-K~+ stress.The K~+-depletion experiments indicated that ZmCIPK23 OE lines showed higher K~+ uptake rates than control plants.However,ZmCIPK23 OE lines displayed a low-K~+-sensitive phenotype,whose shoot K~+ content were slightly decreased under low-K~+ conditions.Further study showed that the K~+content in the older and upper leaves of ZmCIPK23 OE plants were lower than that of control plants under low-K~+ stress,but the K~+ contents in the stem of ZmCIPK23 OE plants were higher.Gene expression analyses indicated that ZmCIPK23 was mainly expressed in root under normal conditions,but low-K~+ treatment could induce its transcriptional level in shoot.These results suggested that ZmCIPK23 may be involved in K~+ uptake and redistribution in maize.Overexpression of ZmCIPK23 may disturb K~+ redistribution in maize shoot,and consequently affects maize K efficiency.In addition,ZmCIPK3 and ZmCIPK9 could also activate the potassium transport activity of ZMK1 when expressed in oocytes.The phenotype and K~+ contents of the ZmCIPK9 and ZmCIPK3 transgenic lines were similar to control plant on low K conditions.The field test experiments showed that reduction of potash fertilizer significantly affected maize growth.At jointing stage,part of the transgenic inbred lines(ZmCBLl transgenic lines and the ZmCIPK9 transgenic lines)showed growth superiority compared with control plants.However,at silking stage,there was no phenotype difference between the transgenic inbred lines and control plants.In summary,the results presented in this dissertation showed that ZmCBL1 and ZmCIPK23 may be involved in K~+ uptake and redistribution in maize.However,constitutive overexpression of ZmCBL1 and ZmCIPK23 cannot enhance maize KUE.It is suggested that the regulatory mechanisms of K~+acquisition and utilization in maize may be different from that in Arabidopsis.The spatial and temporal transcript regulation of ZmCBLl and ZmCIPK23,as well as the proper regulation of their protein activities may be more crucial for maize KUE.The results in this dissertation provide some reference for the genetic improvement of maize KUE in future.