Regulation of Phosphoinositide Metabolism and Early Responses to Osmotic Stress

综述多磷酸化肌醇脂质为植物提供了在细胞内和细胞间传递信号的手段，并且本身是细胞代谢的关键调节剂。植物作为固着生物，通过改变其生长模式来响应大多数环境刺激。PI代谢的持续增加与玉米叶枕细胞伸长和花粉管生长呈正相关，但对植物肌醇磷脂合成的调控知之甚少。磷脂酰肌醇4单磷酸（PtdIns 4P）是植物中最丰富的多磷酸化脂质。因此，研究者推测它是植物信号转导的关键调节因子。有两个编码PtdIns 4-激酶（PtdIns 4K）的基因，PtdIns 4K是合成PtdIns 4P的酶。PtdIns 4K α在植物中与F-肌动蛋白共纯化，并具有一个PH（pleckstrin homology）结构域，这一初步研究结果提出了PH结构域调节PtdIns 4K α活性并协调膜信号与肌动蛋白丝形成的假说。本研究的主要目的是：1.从分子水平和生物化学水平上对上述假说进行验证。分离拟南芥PtdIns 4K α基因敲除突变体，对其进行生物化学和遗传学表征（微阵列分析），并监测其对渗透胁迫的响应;2.鉴定与AtPtdIns 4K α特异性结合的植物蛋白。这些数据对于理解植物作为固着生物如何使用PI途径来感知和响应外部刺激是必不可少的。通过鉴定与脂质激酶相互作用的蛋白质，这项研究将开始建立一个相互作用的信号网络。

SUMMARYPolyphosphorylated inositol lipids provide a means for plants to transmit signals within and between cells as well as being key regulators of cellular metabolism in their own right. Plants as sessile organisms respond to most environmental stimuli by altering their pattern of growth. Sustained increases in PI metabolism correlate positively with cell elongation in maize pulvini and with pollen tube growth, and yet little is known about the regulation of plant inositol phospholipid biosynthesis.Phosphatidylinositol 4 monophosphate (PtdIns4P) is the most abundant of the polyphosphorylated lipids in plants. Thus the investigator hypothesizes that it is a key regulator of plant signal transduction. There are two genes encoding PtdIns 4-kinase (PtdIns4K), the enzyme that synthesizes PtdIns4P. One isoform, PtdIns4Kalpha, copurifies with F-actin in plants and has a PH (pleckstrin homology) domain.This preliminary results lead to the hypothesis that the PH domain regulates PtdIns4Kalpha activity andcoordinates membrane signaling with actin filament formation. The molecular and biochemical tools are available to test these hypotheses.The goals of this project are:1. To isolate PtdIns4Kalpha knockout mutants of Arabidopsis, to characterize them biochemically and genetically (micro-array profiling) and to monitor their response to osmotic stress;2. To identify plant proteins which bind specifically to AtPtdIns4Kalpha. These data are essential to understand how plants as sessile organisms use the PI pathway to sense and respond to external stimuli. By identifying proteins that interact with the lipid kinases, this research will begin to build a network of interacting signaling.