Shi Lihua, Bielawski Jacek, Mu Jinye, Dong Haili, Teng Chong, Zhang Jian, Yang Xiaohui, Tomishige Nario, Hanada Kentaro, Hannun Yusuf A, Zuo Jianru
National Key Laboratory of Plant Genomics, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Datun Road, Beijing 100101, China.
Cell Res. 2007 Dec;17(12):1030-40. doi: 10.1038/cr.2007.100.
Sphingolipids have been suggested to act as second messengers for an array of cellular signaling activities in plant cells, including stress responses and programmed cell death (PCD). However, the mechanisms underpinning these processes are not well understood. Here, we report that an Arabidopsis mutant, fumonisin B1 resistant 11-1 (fbr 11-1), which fails to generate reactive oxygen intermediates (ROIs), is incapable of initiating PCD when the mutant is challenged by fumonisin B(1) (FB(1)), a specific inhibitor of ceramide synthase. Molecular analysis indicated that FBR11 encodes a long-chain base 1 (LCB1) subunit of serine palmitoyltransferase (SPT), which catalyzes the first rate-limiting step of de novo sphingolipid synthesis. Mass spectrometric analysis of the sphingolipid concentrations revealed that whereas the fbr 11-1 mutation did not affect basal levels of sphingoid bases, the mutant showed attenuated formation of sphingoid bases in response to FB(1). By a direct feeding experiment, we show that the free sphingoid bases dihydrosphingosine, phytosphingosine and sphingosine efficiently induce ROI generation followed by cell death. Conversely, ROI generation and cell death induced by dihydrosphingosine were specifically blocked by its phosphorylated form dihydrosphingosine-1-phosphate in a dose-dependent manner, suggesting that the maintenance of homeostasis between a free sphingoid base and its phosphorylated derivative is critical to determining the cell fate. Because alterations of the sphingolipid level occur prior to the ROI production, we propose that the free sphingoid bases are involved in the control of PCD in Arabidopsis, presumably through the regulation of the ROI level upon receiving different developmental or environmental cues.
鞘脂类被认为可作为植物细胞中一系列细胞信号活动的第二信使，包括应激反应和程序性细胞死亡（PCD）。然而，支撑这些过程的机制尚未完全清楚。在此，我们报道了一个拟南芥突变体，伏马菌素B1抗性11-1（fbr 11-1），该突变体无法产生活性氧中间体（ROI），当受到伏马菌素B(1)（FB(1)）（神经酰胺合酶的特异性抑制剂）挑战时，它无法启动PCD。分子分析表明，FBR11编码丝氨酸棕榈酰转移酶（SPT）的长链碱1（LCB1）亚基，该酶催化鞘脂从头合成的第一步限速反应。鞘脂浓度的质谱分析显示，虽然fbr 11-1突变不影响鞘氨醇碱的基础水平，但该突变体在响应FB(1)时鞘氨醇碱的形成减弱。通过直接饲喂实验表明，游离鞘氨醇碱二氢鞘氨醇、植物鞘氨醇和鞘氨醇可有效诱导ROI产生，随后导致细胞死亡。相反，二氢鞘氨醇诱导的ROI产生和细胞死亡被其磷酸化形式二氢鞘氨醇-1-磷酸以剂量依赖的方式特异性阻断，这表明游离鞘氨醇碱与其磷酸化衍生物之间的稳态维持对于决定细胞命运至关重要。由于鞘脂水平的改变发生在ROI产生之前，我们提出游离鞘氨醇碱参与拟南芥中PCD的控制，可能是通过在接收不同发育或环境信号时调节ROI水平来实现的。
