Dynamic Interactions of Plant CNGC Subunits and Calmodulins Drive Oscillatory Ca2+ Channel Activities

First author: Yajun Pan; Affiliations: Capital Normal University (首都师范大学): Beijing, China

Corresponding author: Legong Li

Calcium is a universal signal in all eukaryotes, but the mechanism for encoding calcium signatures remains largely unknown. Calcium oscillations control pollen tube growth and fertilization in flowering plants, serving as a model for dissecting the molecular machines that mediate calcium fluctuations. We report that pollen-tube-specific cyclic nucleotide-gated channels (CNGC18, CNGC8, and CNGC7) together with calmodulin 2 (CaM2) constitute a molecular switch that either opens or closes the calcium channel depending on cellular calcium levels. Under low calcium, calcium-free calmodulin 2 (Apo-CaM2) interacts with CNGC18-CNGC8 complex, leading to activation of the influx channel and consequently increasing cytosolic calcium levels. Calcium-bound CaM2 dissociates from CNGC18/8 heterotetramer, closing the channel and initiating a downturn of cellular calcium levels. We further reconstituted the calcium oscillator in HEK293 cells, supporting the model that Ca2+-CaM-dependent regulation of CNGC channel activity provides an auto-regulatory feedback mechanism for calcium oscillations during pollen tube growth.

钙是所有真核生物都具有的信号，但编码钙信号的分子机制在很大程度上都处于未知状态。在开花植物中钙振荡控制花粉管的生长和植物受精作用，这是解析钙波动分子调控机制的模式系统。作者在本文报道了花粉管特异性环核苷酸门控通道CNGC18、CNGC8和CNGC7与钙调蛋白CaM2一起构成了一个分子开关，依赖于细胞内的钙水平控制该通道的开启或闭合。在低钙水平的情况下，不曾结合钙离子的CaM2（Apo-CaM2）与CNGC18-CNGC8复合物互作，激活钙离子流入通道，进而提高胞质的的钙离子水平。结合钙离子的CaM2会和CNGC18/8异源四聚体分开，从而关闭通道，细胞钙水平开始降低。作者进一步在HEK293细胞中重构了钙振荡，结果证明依赖于Ca2+-CaM的CNGC通道活性调控为花粉管生长过程中的钙振荡提供了一个自动调控反馈机制。

通讯：李乐攻 (http://smkxxy.cnu.edu.cn/szll/zrjs/tpjs/4065.htm)

个人简介：1996年，华东师范大学生物系及中国科学院上海植物生理研究所，博士。

研究方向：逆境或生理反应引起的细胞离子脉冲信号的编码与解码；未知功能膜蛋白家族的筛选和功能解析；细胞有害或有益物质吸收与转运的分子机理。

doi: https://doi.org/10.1016/j.devcel.2018.12.025

Journal: Developmental Cell

Published date: January 31, 2019