湖南农业大学远方等研究人员合作揭示渗透传感器介导的对花粉萌发过程中Ca²⁺脉冲的控制。2024年5月22日，《自然》杂志在线发表了这项成果。

研究人员确定了拟南芥细胞表面真正的低渗透传感器，并发现花粉Ca²⁺脉冲是通过这些低渗透传感器直接受水分控制的，也就是说，Ca²⁺脉冲是水分状态的第二信使。研究人员在大肠杆菌中对低渗透敏感通道进行了功能性表达筛选，并确定了高渗透门控钙离子通道（OSCA）蛋白家族的成员OSCA2.1。

研究人员筛选了单阶和高阶OSCA突变体，观察到osca2.1/osca2.2双基因敲除突变体的花粉萌发和HOSCA能力受损。OSCA2.1和OSCA2.2在植物体内和HEK293细胞中发挥着低渗透敏感性Ca²⁺渗透通道的功能。降低培养基的渗透压会增强花粉的Ca²⁺振荡，这种振荡由OSCA2.1和OSCA2.2介导，是发芽所需的。OSCA2.1和OSCA2.2将细胞外水分状态转化为花粉中的Ca²⁺脉冲，可作为跟踪植物补水情况的重要低渗透传感器。

据介绍，高等植物通过停止细胞活动（脱水）和恢复过程（补水）来度过陆地缺水和水量波动期。然而，植物在补水过程中如何监测水分供应情况尚不清楚。虽然低渗透压诱导的细胞膜Ca²⁺浓度（HOSCA）的增加一直被认为是补水过程中感知低渗透压的机制，但其分子基础仍然未知。由于渗透压会触发膜张力，而渗透压传感通道的渗透压传感特异性只能在体内确定，因此这些通道被归类为机械传感器的一种亚型。

附：英文原文

Title: Osmosensor-mediated control of Ca2+ spiking in pollen germination

Author: Pei, Songyu, Tao, Qi, Li, Wenke, Qi, Guoning, Wang, Borong, Wang, Yan, Dai, Shiwen, Shen, Qiujing, Wang, Xi, Wu, Xiaomei, Xu, Shijian, Theprungsirikul, Lynn, Zhang, Jingyuan, Liang, Liang, Liu, Yuantao, Chen, Kena, Shen, Yang, Crawford, Bridget M., Cheng, Mengjia, Zhang, Qi, Wang, Yiqi, Liu, Hongli, Yang, Benguang, Krichilsky, Bryan, Pei, Jessica, Song, Karen, Johnson, Douglas M., Jiang, Zhonghao, Wu, Feihua, Swift, Gary B., Yang, Huanghe, Liu, Zhonghua, Zou, Xuexiao, Vo-Dinh, Tuan, Liu, Feng, Pei, Zhen-Ming, Yuan, Fang

Issue&Volume: 2024-05-22

Abstract: Higher plants survive terrestrial water deficiency and fluctuation by arresting cellular activities (dehydration) and resuscitating processes (rehydration). However, how plants monitor water availability during rehydration is unknown. Although increases in hypo-osmolarity-induced cytosolic Ca2+ concentration (HOSCA) have long been postulated to be the mechanism for sensing hypo-osmolarity in rehydration1,2, the molecular basis remains unknown. Because osmolarity triggers membrane tension and the osmosensing specificity of osmosensing channels can only be determined in vivo3,4,5, these channels have been classified as a subtype of mechanosensors. Here we identify bona fide cell surface hypo-osmosensors in Arabidopsis and find that pollen Ca2+ spiking is controlled directly by water through these hypo-osmosensors—that is, Ca2+ spiking is the second messenger for water status. We developed a functional expression screen in Escherichia coli for hypo-osmosensitive channels and identified OSCA2.1, a member of the hyperosmolarity-gated calcium-permeable channel (OSCA) family of proteins6. We screened single and high-order OSCA mutants, and observed that the osca2.1/osca2.2 double-knockout mutant was impaired in pollen germination and HOSCA. OSCA2.1 and OSCA2.2 function as hypo-osmosensitive Ca2+-permeable channels in planta and in HEK293 cells. Decreasing osmolarity of the medium enhanced pollen Ca2+ oscillations, which were mediated by OSCA2.1 and OSCA2.2 and required for germination. OSCA2.1 and OSCA2.2 convert extracellular water status into Ca2+ spiking in pollen and may serve as essential hypo-osmosensors for tracking rehydration in plants.

DOI: 10.1038/s41586-024-07445-6

Source: https://www.nature.com/articles/s41586-024-07445-6