PDF(Pubmed)
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 vivo3-5, 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.
摘要：
高等植物通过阻止细胞活动（脱水）和复苏过程（补液）来生存陆地缺水和波动。然而,植物如何在补液过程中监测水的可用性是未知的。尽管长期以来一直认为低渗透压诱导的胞浆Ca2浓度（HOSCA）的增加是感测再液压1,2中的低渗透压的机制，但分子基础仍然未知。由于渗透压会触发膜张力，并且只能在体内确定渗透传感通道的渗透传感特异性3-5，因此这些通道已被分类为机械传感器的亚型。在这里，我们确定了拟南芥中真正的细胞表面低渗透传感器，并发现花粉Ca2加标通过这些低渗透传感器直接由水控制-也就是说，Ca2+尖峰是水状态的第二信使。我们在大肠杆菌中开发了低渗透敏感通道的功能表达筛选，并鉴定了OSCA2.1，这是蛋白质6的高渗透压门控钙渗透通道（OSCA）家族的成员。我们筛选了单个和高阶OSCA突变体，并观察到osca2.1/osca2.2双敲除突变体在花粉萌发和HOSCA中受损。OSCA2.1和OSCA2.2在植物和HEK293细胞中充当低渗透敏感性Ca2+-可渗透通道。降低培养基的渗透压会增强花粉Ca2振荡，它们是由OSCA2.1和OSCA2.2介导的，是发芽所必需的。OSCA2.1和OSCA2.2将细胞外水状态转化为花粉中的Ca2掺入，并可作为必需的低渗透传感器，用于跟踪植物中的补液。
