Li Legong, Kim Beom-Gi, Cheong Yong Hwa, Pandey Girdhar K, Luan Sheng
Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720, USA.
Proc Natl Acad Sci U S A. 2006 Aug 15;103(33):12625-30. doi: 10.1073/pnas.0605129103. Epub 2006 Aug 8.
Nutrient sensing is critical for plant adaptation to the environment. Because of extensive farming and erosion, low content of mineral nutrients such as potassium (K(+)) in soils becomes a limiting factor for plant growth. In response to low-K conditions, plants enhance their capability of K(+) uptake through an unknown signaling mechanism. Here we report the identification of a Ca(2+)-dependent pathway for low-K response in Arabidopsis. We are not aware of any other example of a molecular pathway for a nutrient response in plants. Earlier genetic analyses revealed three genes encoding two Ca(2+) sensors (CBL1 and CBL9) and their target protein kinase (CIPK23) to be critical for plant growth on low-K media and for stomatal regulation, indicating that these calcium signaling components participate in the low-K response and turgor regulation. In this study, we show that the protein kinase CIPK23 interacted with, and phosphorylated, a voltage-gated inward K(+) channel (AKT1) required for K(+) acquisition in Arabidopsis. In the Xenopus oocyte system, our studies showed that interacting calcium sensors (CBL1 and CBL9) together with target kinase CIPK23, but not either component alone, activated the AKT1 channel in a Ca(2+)-dependent manner, connecting the Ca(2+) signal to enhanced K(+) uptake through activation of a K(+) channel. Disruption of both CBL1 and CBL9 or CIPK23 gene in Arabidopsis reduced the AKT1 activity in the mutant roots, confirming that the Ca(2+)-CBL-CIPK pathway functions to orchestrate transporting activities in planta according to external K(+) availability.
营养感知对于植物适应环境至关重要。由于广泛耕种和土壤侵蚀，土壤中钾（K⁺）等矿质营养元素含量低成为植物生长的限制因素。为响应低钾条件，植物通过未知的信号传导机制增强其吸收K⁺的能力。在此，我们报告了拟南芥中一条依赖Ca²⁺的低钾响应途径的鉴定。我们尚未知晓植物中任何其他营养响应分子途径的例子。早期的遗传分析揭示，三个编码两个Ca²⁺传感器（CBL1和CBL9）及其靶蛋白激酶（CIPK23）的基因对于植物在低钾培养基上的生长以及气孔调节至关重要，这表明这些钙信号成分参与低钾响应和膨压调节。在本研究中，我们表明蛋白激酶CIPK23与拟南芥中K⁺获取所需的电压门控内向K⁺通道（AKT1）相互作用并使其磷酸化。在非洲爪蟾卵母细胞系统中，我们的研究表明，相互作用的钙传感器（CBL1和CBL9）与靶激酶CIPK23一起，而非单独的任何一个成分，以Ca²⁺依赖的方式激活AKT1通道，通过激活K⁺通道将Ca²⁺信号与增强的K⁺吸收联系起来。拟南芥中CBL1和CBL9或CIPK23基因的破坏降低了突变体根中的AKT1活性，证实Ca²⁺ - CBL - CIPK途径的功能是根据外部K⁺的可利用性来协调植物体内的转运活动。
