Recognition and response in plant-pathogen interactions

Most plants are resistant to the majority of pathogens. Susceptibility is the exception to the more common state of resistance, i.e., being refractory to infection. However, plant pathogens cause serious economic losses by reducing crop yield and quality. Although such organisms are relatively simple genetic entities, in plants, the mechanisms underlying the generation of disease symptoms and resistance responses are complex and, often, unknown. The study of genes associated with plant-pathogen resistance addresses fundamental questions about the molecular, biochemical, cellular, and physiological means of these interactions. Over the past 10 years, the cloning and analysis of numerous plant resistance genes has led researchers to formulate unifying theories about resistance and susceptibility, and the co-evolution of plant pathogens and their hosts. In this review, we discuss the identification of response genes that have been characterized at the molecular level, as well as their putative links to various signaling pathways. We also summarize the knowledge regarding crosstalk among signaling pathways and plant resistance genes.     

Insulin resistance: Review of the underlying molecular mechanisms

Most human cells utilize glucose as the primary substrate, cellular uptake requiring insulin. Insulin signaling is therefore critical for these tissues. However, decrease in insulin sensitivity due to the disruption of various molecular pathways causes insulin resistance (IR). IR underpins many metabolic disorders such as type 2 diabetes and metabolic syndrome, impairments in insulin signaling disrupting entry of glucose into the adipocytes, and skeletal muscle cells. Although the exact underlying cause of IR has not been fully elucidated, a number of major mechanisms, including oxidative stress, inflammation, insulin receptor mutations, endoplasmic reticulum stress, and mitochondrial dysfunction have been suggested. In this review, we consider the role these cellular mechanisms play in the development of IR.     

Rice–gall midge interactions: Battle for survival

Gall midges are insects specialized in maneuvering plant growth, metabolic and defense pathways for their benefit. The Asian rice gall midge and rice share such an intimate relationship that there is a constant battle for survival by either partner. Diverse responses by the rice host against the midge include necrotic hypersensitive resistance reaction, non-hypersensitive resistance reaction and gall-forming compatible interaction. Genetic studies have revealed that major R (resistance) genes confer resistance to gall midge in rice. Eleven gall midge R genes have been characterized so far in different rice varieties in India. In addition, no single R gene confers resistance against all the seven biotypes of the Asian rice gall midge, and none of the biotypes is virulent against all the resistance genes. Further, the interaction of the plant resistance gene with the insect avirulence gene is on a gene-for-gene basis. Our recent investigations involving suppressive subtraction hybridization cDNA libraries, microarray analyses, gene expression assays and metabolic profiling have revealed several molecular mechanisms, metabolite markers and pathways that are induced, down-regulated or altered in the rice host during incompatible or compatible interactions with the pest. This is also true for some of the pathways studied in the gall midge. Next generation sequencing technology, gene expression studies and conventional screening of gall midge cDNA libraries highlighted molecular approaches adopted by the insect to feed, survive and reproduce. This constant struggle by the midge to overcome the host defenses and the host to resist the pest has provided us with an opportunity to observe this battle for survival at the molecular level.     

Signal transmission in the plant immune response

Genetic and biochemical dissection of signaling pathways regulating plant pathogen defense has revealed remarkable similarities with the innate immune system of mammals and Drosophila. Numerous plant proteins resembling eukaryotic receptors have been implicated in the perception of pathogen-derived signal molecules. Receptor-mediated changes in levels of free calcium in the cytoplasm and production of reactive oxygen species and nitric oxide constitute early events generally observed in plant-pathogen interactions. Positive and negative regulation of plant pathogen defense responses has been attributed to mitogen-activated protein kinase cascades. In addition, salicylic acid, jasmonic acid and ethylene are components of signaling networks that provide the molecular basis for specificity of plant defense responses. This article reviews recent advances in our understanding of early signaling events involved in the establishment of plant disease resistance.     

菌根真菌提高植物抗旱性机制的研究回顾与展望

菌根真菌与全世界约97％的维管植物具有广泛的共生关系.大量研究结果显示菌根植物相比于非菌根植物对于干旱胁迫具有更高的耐受性,说明菌根真菌在植物抗旱过程中发挥着重要作用.本文对近年来国内外在菌根真菌协助植物抵御干旱作用机制方面的研究进行了归纳和总结,主要包括在干旱胁迫下菌根真菌对植物生理学特性的影响机制、菌根真菌提高植物...     

Closing the ranks to attack by powdery mildew

Powdery mildews are among the most common plant diseases, infecting over 650 monocot and over 9000 dicot species. Analysis in domesticated barley and wild Arabidopsis has begun to unravel the genetic and molecular frameworks underlying the mechanisms of susceptibility and resistance to these biotrophic fungal pathogens. This has revealed multiple pathways regulating host defense, some of which are also involved in determining the host range of the pathogen. Host-cell death and rapid cell-wall remodeling have emerged as frequent themes in powdery-mildew resistance. Several mutants have been isolated that might shed light on the enigma of susceptibility determinants in plants.     

水稻抗稻瘟病基因资源与分子育种策略

稻瘟病是水稻主要病害之一。利用抗病品种是防治稻瘟病最经济、有效和安全的措施。近年来,随着植物先天免疫机制、抗病分子生物学以及水稻和稻瘟菌基因组学研究的不断深入,一系列参与病原菌识别和防卫信号传导与应答,以及外源抗菌蛋白、病原菌激发子等抗病相关基因陆续被鉴定和克隆,为提高水稻抗稻瘟病能力提供了一些新的基因资源、育种策略和技术。本文概述了国内外近年来克隆的主要抗稻瘟病基因资源及其在分子育种研究中应用的进展,提出了通过转基因手段整合不同防卫反应关键调控基因的抗稻瘟病聚合育种策略。     

Engineering of plant natural product pathways

Although many important and valuable traits are associated with plant natural products, engineering natural product pathways for plant improvement has often been limited by a lack of understanding of their biochemistry, and by the need for coordinate regulation of multiple gene activities. New approaches are facilitating both the discovery of genes that encode natural products and pathway engineering. Notable successes have been reported in altering complex pathways to improve plant quality and resistance to biotic and abiotic stresses.     

Conservation and divergence of signalling pathways between roots and soil microbes – the Rhizobium-legume symbiosis compared to the development of lateral roots, mycorrhizal interactions and nematode-induced galls

This review compares endophytic symbiotic and pathogenic root–microbe interactions and examines how the development of root structures elicited by various micro-organisms could have evolved by recruitment of existing plant developmental pathways. Plants are exposed to a multitude of soil micro-organisms which affect root development and performance. Their interactions can be of symbiotic and pathogenic nature, both of which can result in the formation of new root structures – how does the plant regulate the different outcomes of interactions with microbes? The idea that pathways activated in plant by micro-organisms could have been `hijacked' from plant developmental pathways is not new, it was essentially proposed by P. S. Nutman in 1948, but at that time, the molecular evidence to support that hypothesis was missing. Genetic evidence for overlaps between different plant–microbe interactions have previously been examined. This review compares the physiological and molecular plant responses to symbiotic rhizobia with those to arbuscular mycorrhizal fungi, pathogenic nematodes and the development of lateral roots and summarises evidence from both molecular and cellular studies for substantial overlaps in the signalling pathways underlying root–micro-organism interactions. A more difficult question has been why plant responses to micro-organisms are so similar, even though the outcomes are very different. Possible hypotheses for divergence of signalling pathways and future approaches to test these ideas are presented.     

Warriors at the gate that never sleep: non-host resistance in plants

The native resistance of most plant species against a wide variety of pathogens is known as non-host resistance (NHR), which confers durable protection to plant species. Only a few pathogens or parasites can successfully cause diseases. NHR is polygenic and appears to be linked with basal plant resistance, a form of elicited protection. Sensing of pathogens by plants is brought about through the recognition of invariant pathogen-associated molecular patterns (PAMPs) that trigger downstream defense signaling pathways. Race-specific resistance, (R)-gene mediated resistance, has been extensively studied and reviewed, while our knowledge of NHR has advanced only recently due to the improved access to excellent model systems. The continuum of the cell wall (CW) and the CW-plasma membrane (PM)-cytoskeleton plays a crucial role in perceiving external cues and activating defense signaling cascades during NHR. Based on the type of hypersensitive reaction (HR) triggered, NHR was classified into two types, namely type-I and type-II. Genetic analysis of Arabidopsis mutants has revealed important roles for a number of specific molecules in NHR, including the role of SNARE-complex mediated exocytosis, lipid rafts and vesicle trafficking. As might be expected, R-gene mediated resistance is found to overlap with NHR, but the extent to which the genes/pathways are common between these two forms of disease resistance is unknown. The present review focuses on the various components involved in the known mechanisms of NHR in plants with special reference to the role of CW-PM components.     

VOCs-mediated hormonal signaling and crosstalk with plant growth promoting microbes

In the natural environment, plants communicate with various microorganisms (pathogenic or beneficial) and exhibit differential responses. In recent years, research on microbial volatile compounds (MVCs) has revealed them to be simple, effective and efficient groups of compounds that modulate plant growth and developmental processes. They also interfere with the signaling process. Different MVCs have been shown to promote plant growth via improved photosynthesis rates, increased plant resistance to pathogens, activated phytohormone signaling pathways, or, in some cases, inhibit plant growth, leading to death. Regardless of these exhibited roles, the molecules responsible, the underlying mechanisms, and induced specific metabolic/molecular changes are not fully understood. Here, we review current knowledge on the effects of MVCs on plants, with particular emphasis on their modulation of the salicylic acid, jasmonic acid/ethylene, and auxin signaling pathways. Additionally, opportunities for further research and potential practical applications presented.     

肥胖诱发胰岛素抵抗的炎性机制

肥胖可诱发一系列慢性代谢性疾病,如2型糖尿病、血脂障碍、高血压和非酒精性脂肪肝等.这些疾病构成了当今世界人类健康的极大威胁.胰岛素抵抗是这些疾病的共有特征.胰岛素抵抗的发生与慢性低度系统炎性密切相关,涉及多条炎性信号通路的激活和胰岛素信号转导的缺陷.本文综述了肥胖、炎性与胰岛素抵抗之间的本质联系,以及肥胖诱发胰岛素抵抗的炎性机制,以期为肥胖相关疾病的防治提供重要参考.     

Transgenic approaches to microbial disease resistance in crop plants

Recent progress in the genetic dissection of plant disease resistance signaling pathways has opened a number of new avenues towards engineering pathogen resistance in crops. Genes controlling race-specific and broad-spectrum resistance responses have been cloned, and novel induced resistance pathways have been identified in model and crop systems. Advances continue to be made in identification of antifungal proteins with effects inhibitory to either pathogen development or accumulation of associated mycotoxins.     

植物细胞壁介导的抗病性及其分子机制

本文简要介绍植物与病原菌在细胞壁层面上的相互作用,并从植物细胞对受侵过程中细胞壁损伤的感知、细胞壁损伤引起植物抗病信号途径的活化、植物细胞壁防卫反应的分子机制等方面重点概述植物细胞壁抗性及其分子机制。     

Plant immune responses triggered by beneficial microbes

Beneficial soil-borne microorganisms, such as plant growth promoting rhizobacteria and mycorrhizal fungi, can improve plant performance by inducing systemic defense responses that confer broad-spectrum resistance to plant pathogens and even insect herbivores. Different beneficial microbe-associated molecular patterns (MAMPs) are recognized by the plant, which results in a mild, but effective activation of the plant immune responses in systemic tissues. Evidence is accumulating that systemic resistance induced by different beneficials is regulated by similar jasmonate-dependent and ethylene-dependent signaling pathways and is associated with priming for enhanced defense.     

沙冬青逆境胁迫分子生物学研究进展

逆境胁迫是影响植物生长发育的重要因素,植物的抗逆机理是分子生物学研究的重要领域。随着分子生物学技术的发展,有关植物抗逆方面的研究已取得了很大的进展,初步揭示了植物应对逆境胁迫适应性的分子机理。沙冬青是我国温带荒漠地区惟一的常绿灌木,具有很强的抗逆性,是开展植物逆境胁迫研究和抗逆基因筛选的理想材料。本文综合论述了抗逆植物沙冬青的抗逆机理及逆境胁迫相关基因的分子生物学研究进展,为植物抗逆基因工程发掘更多的基因资源和抗旱植物的抗逆性研究提供思路。     

Inhibition of ceramide production reverses TNF-induced insulin resistance

Ceramide has been implicated as a mediator of insulin resistance induced by tumor necrosis factor-alpha (TNF) in adipocytes. Adipocytes contain numerous caveolae, sphingolipid and cholesterol-enriched lipid microdomains, that are also enriched in insulin receptor (IR). Since caveolae may be important sites for crosstalk between tyrosine kinase and sphingolipid signaling pathways, we examined the role of increased caveolar pools of ceramide in regulating tyrosine phosphorylation of the IR and its main substrate, insulin receptor substrate-1 (IRS-1). Neither exogenous short-chain ceramide analogs nor pharmacologic increases in endogenous caveolar pools of ceramide inhibited insulin-induced tyrosine phosphorylation of the IR and IRS-1. However, inhibition of TNF-induced caveolar ceramide production reversed the decrease in IR tyrosine phosphorylation in response to TNF. These results suggest that TNF-independent increases in caveolar pools of ceramide are not sufficient to inhibit insulin signaling but that in conjunction with other TNF-dependent signals, caveolar pools of ceramide are a critical component for insulin resistance by TNF.     

茶树诱导抗虫性的研究进展

为了抵御植食性昆虫的为害,植物在进化过程中形成了包括组成抗性和诱导抗性在内的复杂防御体系.在通过受体识别茶树害虫为害后,茶树会启动早期信号事件,继而激活茉莉酸、水杨酸、乙烯和赤霉素等植物激素信号通路,从而引起次生代谢物的积累,最终对害虫产生直接和间接抗性.基于近年来茶树害虫为害诱导的茶树防御反应及其相关调控机理的研究进...