Reactive Oxygen Species during Plant-microorganism Early Interactions

Reactive Oxygen Species (ROS) are continuously produced as a result of aerobic metabolism or in response to biotic and abiotic stresses. ROS are not only toxic by-products of aerobic metabolism, but are also signalling molecules involved in several developmental processes in all organisms. Previous studies have clearly shown that an oxidative burst often takes place at the site of attempted invasion during the early stages of most plant-pathogen interactions. Moreover, a second ROS production can be observe...     

植物细胞活性氧种类、代谢及其信号转导

越来越明显的证据表明,植物体十分活跃的产生着活性氧并将之作为信号分子、进而控制着诸如细胞程序性死亡、非生物胁迫响应、病原体防御和系统信号等生命过程,而不仅是传统意义上的活性氧是有氧代谢的附产物。日益增多的证据显示,由脱落酸、水杨酸、茉莉酸与乙烯以及活性氧所调节的激素信号途径,在生物和非生物胁迫信号的“交谈”中起重要作用。活性氧最初被认为是动物吞噬细胞在宿主防御反应时所释放的附产物,现在的研究清楚的表明,活性氧在动物和植物细胞信号途径中均起作用。活性氧可以诱导细胞程序性死亡或坏死、可以诱导或抑制许多基因的表达,也可以激活上述级联信号。近来生物化学与遗传学研究证实过氧化氢是介导植物生物胁迫与非生物胁迫的信号分子,过氧化氢的合成与作用似乎与一氧化氮有关系。过氧化氢所调节的下游信号包括钙“动员”、蛋白磷酸化和基因表达等。     

Reactive oxygen and nitrogen species and glutathione: key players in the legume-Rhizobium symbiosis

Several reactive oxygen and nitrogen species (ROS/RNS) are continuously produced in plants as by-products of aerobic metabolism or in response to stresses. Depending on the nature of the ROS and RNS, some of them are highly toxic and rapidly detoxified by various cellular enzymatic and non-enzymatic mechanisms. Whereas plants have many mechanisms with which to combat increased ROS/RNS levels produced during stress conditions, under other circumstances plants appear to generate ROS/RNS as signalling molecules to control various processes encompassing the whole lifespan of the plant such as normal growth and development stages. This review aims to summarize recent studies highlighting the involvement of ROS/RNS, as well as the low molecular weight thiols, glutathione and homoglutathione, during the symbiosis between rhizobia and leguminous plants. This compatible interaction initiated by a molecular dialogue between the plant and bacterial partners, leads to the formation of a novel root organ capable of fixing atmospheric nitrogen under nitrogen-limiting conditions. On the one hand, ROS/RNS detection during the symbiotic process highlights the similarity of the early response to infection by pathogenic and symbiotic bacteria, addressing the question as to which mechanism rhizobia use to counteract the plant defence response. Moreover, there is increasing evidence that ROS are needed to establish the symbiosis fully. On the other hand, GSH synthesis appears to be essential for proper development of the root nodules during the symbiotic interaction. Elucidating the mechanisms that control ROS/RNS signalling during symbiosis could therefore contribute in defining a powerful strategy to enhance the efficiency of the symbiotic interaction.     

Nitric oxide function and signalling in plant disease resistance

Nitric oxide (NO) is one of only a handful of gaseous signalling molecules. Its discovery as the endothelium-derived relaxing factor (EDRF) by Ignarro revolutionized how NO and cognate reactive nitrogen intermediates, which were previously considered to be toxic molecules, are viewed. NO is now emerging as a key signalling molecule in plants, where it orchestrates a plethora of cellular activities associated with growth, development, and environmental interactions. Prominent among these is its function in plant hypersensitive cell death and disease resistance. While a number of sources for NO biosynthesis have been proposed, robust and biologically relevant routes for NO production largely remain to be defined. To elaborate cell death during an incompatible plant-pathogen interaction NO functions in combination with reactive oxygen intermediates. Furthermore, NO has been shown to regulate the activity of metacaspases, evolutionary conserved proteases that may be intimately associated with pathogen-triggered cell death. NO is also thought to function in multiple modes of plant disease resistance by regulating, through S-nitrosylation, multiple nodes of the salicylic acid (SA) signalling pathway. These findings underscore the key role of NO in plant-pathogen interactions.     

植物过氧化物酶体在活性氧信号网络中的作用

过氧化物酶体是高度动态、代谢活跃的细胞器,主要参与脂肪酸等脂质的代谢及产生和清除不同的活性氧(reactive oxygen species, ROS)。ROS是细胞有氧代谢的副产物。当胁迫长期作用于植物,过量的ROS会引起氧胁迫,损害细胞结构和功能的完整性,导致细胞代谢减缓,活性降低,甚至死亡;但低浓度的ROS则作为分子信号,感应细胞ROS/氧化还原变化,从而触发由环境因素导致的过氧化物酶体动力学以及依赖ROS信号网络改变而产生快速、特异性的应答。ROS也可以通过直接或间接调节细胞生长来控制植物的发育,是植物发育的重要调节剂。此外,过氧化物酶体的动态平衡由ROS、过氧化物酶体蛋白酶及自噬过程调节,对于维持细胞的氧化还原平衡至关重要。本文就过氧化物酶体中ROS的产生和抗氧化剂的调控机制进行综述,以期为过氧化物酶体如何感知环境变化,以及在细胞应答中,ROS作为重要信号分子的研究提供参考。     

植物与病原菌互作的蛋白质组学研究进展

深入认识植物与病原菌的识别方式、亲和性或非亲和性的互作模式,对于揭示植物-病原菌互作机制研究具有重要意义.利用蛋白质组学方法研究病原菌侵染植物过程,分析相关的基因和蛋白,有助于从分子水平上探究植物-病原菌相互作用机制.本文概述了植物-病原菌的互作机制,系统介绍了差异蛋白质组学分析方法在植物-病原真菌、植物-病原细菌两类互作系统中的应用,分析了植物与病原菌互作过程中可能涉及的差异表达功能蛋白,并对当前蛋白质组学技术在植物与病原菌互作研究中存在的诸多问题进行了探讨.     

Challenging Xanthomonas campestris with low levels of arsenic mediates cross-protection against oxidant killing

Xanthomonas encounters highly toxic reactive oxygen species (ROS) from many sources, such as those generated by plants against invading bacteria, other soil bacteria and from aerobic respiration. Thus, conditions that alter intracellular ROS levels such as exposure to toxic metalloids would have profound effects on bacterial physiology. Here, we report that exposure of Xanthomonas campestris pv. phaseoli (Xp) to low levels of arsenic induces physiological cross-protection against killing by H(2)O(2) and organic hydroperoxide but not a superoxide generator. Cross-protection against H(2)O(2) and organic hydroperoxide toxicity was due to increased expression of genes encoding major peroxide-metabolizing enzymes such as alkyl hydroperoxide reductase (AhpC), catalase (KatA) and organic hydroperoxide resistance protein (Ohr). Arsenic-induced protection against H(2)O(2) and organic hydroperoxide requires the peroxide stress response regulators, OxyR and OhrR, respectively. Moreover, analyses of double mutants of the major H(2)O(2) and organic hyproperoxide-scavenging enzymes, Xp ahpC katA and Xp ahpC ohr, respectively, suggested the existence of unidentified OxyR- and OhrR-regulated genes that are involved in arsenic-induced resistance to H(2)O(2) and organic hyproperoxide killing in Xp. These arsenic-induced physiological alterations could play an important role in bacterial survival both in the soil environment and during plant-pathogen interactions.     

Reactive oxygen species and their role in plant defence and cell wall metabolism

Harnessing the toxic properties of reactive oxygen species (ROS) to fight off invading pathogens can be considered a major evolutionary success story. All aerobic organisms have evolved the ability to regulate the levels of these toxic intermediates, whereas some have evolved elaborate signalling pathways to dramatically increase the levels of ROS and use them as weapons in mounting a defence response, a process commonly referred to as the oxidative burst. The balance between steady state levels of ROS and the exponential increase in these levels during the oxidative burst has begun to shed light on complex signalling networks mediated by these molecules. Here, we discuss the different sources of ROS that are present in plant cells and review their role in the oxidative burst. We further describe two well-studied ROS generating systems, the NADPH oxidase and apoplastic peroxidase proteins, and their role as the primary producers of ROS during pathogen invasion. We then discuss what is known about the metabolic and proteomic fluxes that occur in plant cells during the oxidative burst and after pathogen recognition, and try to highlight underlying biochemical processes that may provide more insight on the complex regulation of ROS in plants.     

Plant-induced cell death in the oomycete pathogen Phytophthora parasitica

The activation of programmed cell death in the host during plant-pathogen interactions is an important component of the plant disease resistance mechanism. In this study we show that activation of programmed cell death in microorganisms also regulates plant-pathogen interactions. We found that a form of vacuolar cell death is induced in the oomycete Phytophthora parasitica--the agent that causes black shank disease in Nicotiana tabacum--by extracellular stimuli from resistant tobacco. The single-celled zoospores underwent cell death characterized by dynamic membrane rearrangements, cell shrinkage, formation of numerous large vacuoles in the cytoplasm and degradation of cytoplasmic components before plasma membrane disruption. Phytophthora cell death required protein synthesis but not caspase activation, and was associated with the production of intracellular reactive oxygen species. This characterization of plant-mediated cell death signalling in pathogens will enhance our understanding of the biological processes regulating plant-pathogen interactions, and improve our ability to control crop diseases.     

A burst of plant NADPH oxidases

Reactive oxygen species (ROS) are highly reactive molecules able to damage cellular components but they also act as cell signalling elements. ROS are produced by many different enzymatic systems. Plant NADPH oxidases, also known as respiratory burst oxidase homologues (RBOHs), are the most thoroughly studied enzymatic ROS-generating systems and our understanding of their involvement in various plant processes has increased considerably in recent years. In this review we discuss their roles as ROS producers during cell growth, plant development and plant response to abiotic environmental constraints and biotic interactions, both pathogenic and symbiotic. This broad range of functions suggests that RBOHs may serve as important molecular 'hubs' during ROS-mediated signalling in plants.     

Interactions between hormone and redox signalling pathways in the control of growth and cross tolerance to stress

The ability of plants to respond to a wide range of environmental stresses is highly flexible and finely balanced through the interaction of hormonal plant growth regulators and the redox signalling hub, which integrates information from the environment and cellular metabolism/physiology. Plant hormones produce reactive oxygen species (ROS) as second messengers in signalling cascades that convey information concerning changes in hormone concentrations and/or sensitivity to mediate a whole range of adaptive responses. Cellular redox buffering capacity that is determined largely by the abundance of ascorbate has a profound influence on the threshold at which hormone signalling is triggered and on the interactions between different hormones. Other antioxidants such as glutathione, glutaredoxins and thioredoxins are also central redox regulators of hormone signalling pathways. The complex network of cross-communication between oxidants and antioxidants in the redox signalling hub and the different hormone signalling pathways maximises productivity under stress-free situations and regulates plant growth, development, reproduction, programmed cell death and survival upon exposure to stress. This interactive network confers enormous regulatory potential because it allows plants to adapt to changing and often challenging conditions, while preventing boom or bust scenarios with regard to resources, ensuring that energy is produced and utilised in a safe and efficient manner.     

Mitochondrial redox control of matrix metalloproteinases

Reactive oxygen species (ROS) are constantly generated in aerobic organisms during normal metabolism and in response to both internal and external stimuli. Imbalances in the production and removal of ROS have been hypothesized to play a causative role in numerous disease pathologies such as cancer, ischemia/reperfusion injury, and degenerative diseases such as photoaging, atherosclerosis, arthritis, and neurodegeneration. A feature often associated with these diseases is a malfunctioning of the connective tissue remodeling process due to increased activity of extracellular matrix-degrading metalloproteinases (MMPs). This review summarizes the evidence that implicates ROS as key regulators of MMP production and the importance of these interactions in disease pathologies.     

Genetic elucidation of nitric oxide signaling in incompatible plant-pathogen interactions

Recent experiments indicate that nitric oxide (NO) plays a pivotal role in disease resistance and several other physiological processes in plants. However, most of the current information about the function of NO in plants is based on pharmacological studies, and additional approaches are therefore required to ascertain the role of NO as an important signaling molecule in plants. We have expressed a bacterial nitric oxide dioxygenase (NOD) in Arabidopsis plants and/or avirulent Pseudomonas syringae pv tomato to study incompatible plant-pathogen interactions impaired in NO signaling. NOD expression in transgenic Arabidopsis resulted in decreased NO levels in planta and attenuated a pathogen-induced NO burst. Moreover, NOD expression in plant cells had very similar effects on plant defenses compared to NOD expression in avirulent Pseudomonas. The defense responses most affected by NO reduction during the incompatible interaction were decreased H(2)O(2) levels during the oxidative burst and a blockage of Phe ammonia lyase expression, the key enzyme in the general phenylpropanoid pathway. Expression of the NOD furthermore blocked UV light-induced Phe ammonia lyase and chalcone synthase gene expression, indicating a general signaling function of NO in the activation of the phenylpropanoid pathway. NO possibly functions in incompatible plant-pathogen interactions by inhibiting the plant antioxidative machinery, and thereby ensuring locally prolonged H(2)O(2) levels. Additionally, albeit to a lesser extent, we observed decreases in salicylic acid production, a diminished development of hypersensitive cell death, and a delay in pathogenesis-related protein 1 expression during these NO-deficient plant-pathogen interactions. Therefore, this genetic approach confirms that NO is an important regulatory component in the signaling network of plant defense responses.     

Nitric oxide-induced salt stress tolerance in plants: ROS metabolism,signaling, and molecular interactions

Nitric oxide (NO), a non-charged, small, gaseous free-radical, is a signaling molecule in all plant cells. Several studies have proposed multifarious physiological roles for NO, from seed germination to plant maturation and senescence. Nitric oxide is thought to act as an antioxidant, quenching ROS during oxidative stress and reducing lipid peroxidation. NO also mediates photosynthesis and stomatal conductance and regulates programmed cell death, thus providing tolerance to abiotic stress. In mitochondria, NO participates in the electron transport pathway. Nitric oxide synthase and nitrate reductase are the key enzymes involved in NO-biosynthesis in aerobic plants, but non-enzymatic pathways have been reported as well. Nitric oxide can interact with a broad range of molecules, leading to the modification of protein activity, GSH biosynthesis, S-nitrosylation, peroxynitrite formation, proline accumulation, etc., to sustain stress tolerance. In addition to these interactions, NO interacts with fatty acids to form nitro-fatty acids as signals for antioxidant defense. Polyamines and NO interact positively to increase polyamine content and activity. A large number of genes are reprogrammed by NO; among these genes, proline metabolism genes are upregulated. Exogenous NO application is also shown to be involved in salinity tolerance and/or resistance via growth promotion, reversing oxidative damage and maintaining ion homeostasis. This review highlights NO-mediated salinity-stress tolerance in plants, including NO biosynthesis, regulation, and signaling. Nitric oxide-mediated ROS metabolism, antioxidant defense, and gene expression and the interactions of NO with other bioactive molecules are also discussed. We conclude the review with a discussion of unsolved issues and suggestions for future research.     

Experimental systems to assess the effects of reactive oxygen species in plant tissues

Reactive oxygen species (ROS) are continuously produced in several organelles during aerobic metabolism. Furthermore, a wide range of environmental stresses such as chilling, salinity, drought and high light, lead to an elevated production of ROS. ROS can react with biomolecules and cause oxidative damage and even necrosis. Antioxidants and antioxidant-enzymes function to interrupt the cascades of uncontrolled oxidation. On the other hand, ROS influence the expression of genes playing a central role in many signaling pathways. Tools like the exogenous application of oxidative stress-causing agents and the in planta production of ROS in mutants altered in ROS metabolism are increasingly used to assess specific and common responses toward different types of ROS signals. The major challenge is the identification of ROS sensors and signaling components to finally elucidate the molecular mechanisms of oxidative stress response in plants.Key words: Arabidopsis thaliana, oxidative damage, reactive oxygen species, signaling