Functional Genomics of the Arabidopsis gp91-phox NADPH Oxidase Family

植物通过特定的防御机制识别和响应病原体的攻击。植物体内由分子氧快速产生的活性氧中间体(ROI)与植物对病原菌的抗性反应有关。这些氧衍生物对入侵的微生物是有毒的，可以作为被入侵的植物细胞的信号。ROI的积累经常与超敏反应(HR)有关，HR是一种程序性细胞死亡(PCD)，可能也需要一氧化氮(NO)的形成。此外，ROI还在细胞伸长、细胞壁强化、木质化等形态发生现象中发挥作用，以及对其他胁迫的反应，如昆虫伤害攻击、盐胁迫和低温胁迫。发育调控细胞死亡的例子包括木质部等特化结构的形成、器官塑形(某些叶裂片的形成、花器官败育)、器官完成其功能后的退化(胚柄或种子萌发后的糊粉和胚乳)和衰老。在花中，花药室(绒毡层)的内部细胞层在花粉发育过程中经历PCD。ROI在这些过程中的作用在很大程度上还没有被探索。已经提出了几种生物化学机制来解释植物ROI的产生。然而，各种证据表明，NADPH氧化酶，类似于在哺乳动物吞噬细胞中产生呼吸爆发的酶，作为在植物中检测到的ROI的来源，至少是在感染上。这位研究者已经发现在哺乳动物gp91Phox的8个拟南芥Atrbohomolos的编码区插入转座子，这是迄今为止发现的与NADPH结合的黄色素b558的关键膜。这些突变系是分析特定gp91Phox同源物的作用的无与伦比的工具，不仅在植物防御中，而且与发育过程、PCD和其他对环境的反应有关。初步数据表明，该基因家族存在冗余，并且通过gp91-Phox蛋白产生的ROI在至少一个关键的发育过程中发挥作用。Atrboh基因的鉴定使PI能够在信号转导途径的早期寻找更多的成分进行防御，并研究激活植物NADPH氧化酶的机制。

Plants recognize and respond to pathogen attack with specific defensemechanisms. The rapid production of Reactive Oxygen Intermediates (ROI),from molecular oxygen, in plants has been correlated with resistanceresponses against pathogens. These oxygen derivatives can be toxic toinvading microbes and can serve as signals to the plant cells beinginvaded. ROI accumulation is frequently correlated with the HypersensitiveResponse (HR), a kind of programmed cell death (PCD) which probably alsorequires nitric oxide (NO) formation. In addition, ROI play a role inmorphogenetic phenomena like cell elongation, strengthening of the cellwall, lignification and response to other stresses such as wounding attackby insects, saline and cold stress. Examples of developmentally regulatedcell death include the formation of specialized structures like xylem,organ sculpting (formation of certain leaf lobes, floral organ abortion),the degeneration of organs once they have accomplished their function (theembryo suspensor, or the aleurone and the endosperm after the seedgermination) and senescence. In flowers, the interior cell layer of theanther locule (the tapetum) undergoes PCD during pollen development. Therole of ROI in these processes is largely unexplored.Several biochemical mechanisms have been proposed to explain ROI generationby plants. However, various lines of evidence implicate an NADPH oxidase,analogous to that which generates the respiratory burst in mammalianphagocytes, as the source of the ROI detected in plants, at least uponinfection.This investigator has found transposon insertions in the coding region of 8 Arabidopsis Atrbohhomologs of the mammalian gp91phox, the key membrane bound NADPH-bindingflavocytochrome b558 so far identified. These mutant lines are anincomparable tool to dissect the role of specific gp91phox homologues, notonly in plant defense but also in relation to developmental processes, PCDand other responses to the environment. Preliminary data demonstratethat there is redundancy in this gene family, and that ROI generated viathe gp91-phox protein play a role in at least one critical developmentalprocess.The identification of the Atrboh genes enables the PI to look for morecomponents in early steps of the signal transduction pathway to defense,and to study the mechanism that activates the plant NADPH oxidase.