The Arabidopsis gp91-phox Gene Family and NADPH Oxidase Function

植物无法移动来保护自己免受环境中的侵害。 此外，它们不像脊椎动物那样拥有复杂的、循环的、基于细胞的免疫防御系统。然而，植物已经进化出一种用于识别病原体的免疫系统，该系统会启动一系列细胞反应，共同阻止入侵者或对应激情况做出反应和反应。活性氧（ROI）的产生是植物感染病原体后观察到的早期反应之一。 产生的 ROI 可能直接参与杀死入侵病原体，但也可以作为诱导进一步防御的信号。质膜结合的 NADPH 氧化酶可能是植物 ROI 的来源。这种氧化酶也称为呼吸爆发氧化酶 (RBO)，最初是在哺乳动物巨噬细胞中描述的，是一种介导杀死微生物的多酶复合物。这种蛋白质是 NADPH 氧化酶的酶亚基，利用分子氧产生超氧化物。拟南芥有一个由 10 个成员组成的 Atrboh 基因家族（拟南芥呼吸爆发氧化酶同源物），与名为 gp91phox 的动物蛋白同源。然而，NADPH 氧化酶的精确亚基结构及其激活调节似乎与哺乳动物巨噬细胞不同。越来越明显的是，ROI 不是刽子手，而是介导防御激活以及对环境和发育过程的其他反应的信号。在哺乳动物中，gp91phox 的多种亚型在不同的细胞类型中发挥作用，并执行不同的功能。同样，植物中不同的 NADPH 氧化酶也可能介导不同组织中质外体 ROI 的产生以及对不同环境刺激的反应。例如，我们的小组已经表明，AtrbohD 和 AtrbohF 负责防御反应期间 ROI 的产生，并且通过 Atrboh 家族的这些成员产生的 ROI 是气孔关闭期间 ABA 信号传导中的第二信使。此外，AtrbohC 介导的氧化爆发通过激活允许钙进出细胞的通道，在根毛形成过程中调节植物细胞的扩张。有趣的是，一氧化氮 (NO)，另一种介导哺乳动物巨噬细胞细胞死亡的反应分子，可能与 ROI 一起调节植物反应。研究表明，与病原体的相互作用会触发 NO 释放，然后 ROI 和 NO 似乎可以协同作用来控制过敏反应。该项目的目标是使用功能基因组学工具破译植物 NADPH 氧化酶基因家族的功能。要测试的假设是 Atrboh 的不同成员（植物 NADPH 氧化酶的组成部分）在防御反应和发育过程、PCD 和其他环境反应中控制 ROI 的产生。 ROI 和 NO（PCD 和其他反应的另一个重要调节因子）之间的联系也将被研究。 Atrboh 基因的鉴定还能够研究激活植物 NADPH 氧化酶的机制。这是特别相关的，因为哺乳动物 NADPH 氧化酶的重要调节元件在植物氧化酶中似乎不存在。将进行研究以确定 ROI 信号传导的更多成分，特别是那些参与调节 Atrboh 功能的信号转导途径早期步骤的成分，以及 ROI 依赖性信号传导的推定靶标或介质。这些研究将有助于进一步了解 ROI 在抗病反应期间以及在 ROI 和 NO 介导的一系列发育反应中的功能。

Plants cannot move to defend themselves from aggressions in their environment. Also they do not posses a complex, circulating, cell-based immunological system of defense like vertebrates. However, plants have evolved an immune system for pathogen recognition that initiates a set of cellular responses that collectively stop the intruder or can react and respond to stress situations. Production of Reactive Oxygen Species (ROI) is one of the earlier responses observed after pathogen infection in plants. ROI produced may directly participate in the killing of the invading pathogens, but could also act as a signal that induces further defenses. A plasma membrane bound NADPH oxidase is the likely source of ROI in plants. This oxidase, also known as the respiratory burst oxidase (RBO), was initially described in mammalian macrophages and is a multienzymatic complex that mediate the killing of microbes. This protein is the enzymatic subunit of the NADPH oxidase that uses molecular oxygen to make superoxide. Arabidopsis has a 10 member Atrboh (Arabidopsis thaliana respiratory burst oxidase homologs), gene family, homologous to the animal protein called gp91phox. However, the precise subunit structure of the NADPH oxidase and the regulation of its activation appear to be different than in mammalian macrophages.It is becoming evident that ROI is not an executioner but a signal that mediate the activation of the defenses as well as other responses to the environment and developmental processes. In mammals, multiple isoforms of gp91phox act in different cell types, and perform different functions. Similarly, different NADPH oxidases in plants may also mediates production of apoplastic ROI in different tissues and in responses to different environmental stimuli. For example, our group has shown that AtrbohD and AtrbohF are responsible for the production of ROI during the defense response and that ROI generated through these members of the Atrboh family are required as second messengers in ABA signaling during stomata closure. Also, the oxidative burst mediated by AtrbohC regulates plant cell expansion during root hair formation through the activation of channels that allow calcium to move in and out of the cell.. Interestingly, Nitric Oxide (NO), another reactive molecule that mediates cell death in mammalian macrophages, may regulate plant responses in conjunction to ROI. Studies show that interaction with pathogens trigger NO release, and ROI and NO seem to, then, work synergistically to control the hypersensitive response.The goal of this project is to decipher, using functional genomics tools, the functions of the plant NADPH oxidase gene family. The hypothesis to be tested is that different members of Atrboh, components of the plant NADPH oxidase, control production of ROI during defense response and in developmental processes, PCD and other responses to the environment. The connections between ROI and NO, another important regulator of PCD and other responses, will be also investigated. The identification of the Atrboh genes also enables to study the mechanism that activates the plant NADPH oxidase. This is particularly relevant since important regulatory elements of the mammalian NADPH oxidase appear to be absent in the plant oxidase. Studies will be conducted to identify more components of the ROI signaling, especially those involved in earlier steps of the signal transduction pathway that regulate Atrboh function, as well as putative targets or mediators of ROI-dependent signaling. These studies will allow to further understand the function of ROI during disease resistance responses, as well as in a range of developmental responses mediated by ROI and NO.