Defense Response to Pathogens Through Epigenetic Regulation in Rice

Epigenetic factors have recently emerged as key regulators of the defense response to pathogens in plants. The epigenetic mechanisms underlying defense regulation have been investigated mostly in Arabidopsis, while our understanding of the epigenetic regulation of defense in rice is limited. In this review, we summarize recent findings surrounding epigenetic mechanisms for defense in rice, primarily focusing on DNA methylation, histone modification, and small RNA regulation. In particular, we focused on RNA-directed DNA methylation (RdDM) and other epigenetic regulatory mechanisms that are involved in disease resistance. Finally, we explored potential epigenetic factors that might regulate the defense response in rice by analyzing available microarray data that can be used to uncover details of epigenetics regulation.     

表观遗传调控植物响应非生物胁迫的研究进展

植物的生长发育容易受到外界环境变化的影响。非生物胁迫发生时, 表观遗传机制对胁迫应答基因的表达调控发挥了十分重要的作用。近年来, 调控植物非生物胁迫应答的表观遗传机制研究取得了一系列重要进展, 为进一步深入解析植物响应非生物胁迫的分子机制奠定了基础。该文对DNA甲基化修饰、组蛋白修饰、染色质重塑和非编码RNA等主要表观遗传调控方式在植物响应非生物胁迫中的作用进行了简要综述。     

Regulation of Plant Defense Response to Fungal Pathogens: Two Types of Protein Kinases in the Reversible Phosphorylation of the Host Plasma Membrane H+-ATPase

The role of reversible phosphorylation of the host plasma membrane H+-ATPase in signal transduction during the incompatible interaction between tomato cells and the fungal pathogen Cladosporium fulvum was investigated. Tomato cells (with the Cf-5 resistance gene) or isolated plasma membranes from Cf-5 cells treated with elicitor preparations from race 2.3 or 4 of C. fulvum (containing the avr5 gene product) showed a marked dephosphorylation of plasma membrane H+-ATPase. Similar treatment with elicitor preparations from races 5 and 2.4.5.9.11 (lacking the avr5 gene product) showed no change in dephosphorylation. Elicitor (race 4) treatment of cells, but not of isolated plasma membranes, for 2 hr resulted in rephosphorylation of the ATPase via Ca2+-dependent protein kinases. The initial (first hour) rephosphorylation was enhanced by protein kinase C (PKC) activators and was prevented by PKC inhibitors. Activity of a second kinase appeared after 1 hr and was responsible for the continuing phosphorylation of the H+-ATPase. This latter Ca2+-dependent kinase was inhibited by a calmodulin (CaM) antagonist and by an inhibitor of Ca2+/CaM-dependent protein kinase II. The activation of the Ca2+/CaM-dependent protein kinase depended on the prior activation of the PKC-like kinase.     

Root Defense Responses to Fungal Pathogens: A Molecular Perspective

This review will focus on the molecular and genetic mechanisms underlying defense responses of roots to fungal pathogens. Soil-borne pathogens, including Phytophthora, Pythium, Fusarium, and Bipolaris, represent major sources of biotic stress in the rhizosphere and roots of plants. Molecular recognition and signaling leading to effective resistance has been demonstrated to occur between host and Phytophthora, or Pythium. The hypersensitive response and apoptotic cell death, two oxidative processes that limit biotrophic pathogens, generally act to exacerbate disease symptoms induced by necrotrophic organisms. Although pathogenesis-related proteins can be expressed in roots during pathogen challenge, salicylic acid has not been implicated in root-mediated interactions. Jasmonic acid and ethylene have been found to mediate parallel as well as synergistic pathways that confer partial tolerance to necrotrophic pathogens, as well as induced systemic resistance to root and foliar pathogens. Genomics approaches are revealing new networks of defense-signaling pathways, and have the potential of elucidating those pathways that are important in root-defense responses.     

Plant Defense Response to Fungal Pathogens (II. G-Protein-Mediated Changes in Host Plasma Membrane Redox Reactions)

Elicitor preparations containing the avr5 gene products from races 4 and 2.3 of Cladosporium fulvum, and tomato (Lycopersicon esculentum L.) cells containing the resistance gene Cf5 were used to investigate the involvement of redox processes in the production of active oxygen species associated with the plant response to the fungal elicitors. Here we demonstrate that certain race-specific elicitors of C. fulvum induced an increase in ferricyanide reduction in enriched plasma membrane fractions of tomato cells. The addition of elicitors to plasma membranes also induced increases in NADH oxidase and NADH-dependent cytochrome c reductase activities, whereas ascorbate peroxidase activity was decreased. These results suggest that changes in the host plasma membrane redox processes, transferring electrons from reducing agents to oxygen, could be involved in the increased production of active oxygen species by the race-specific elicitors. Our results also show that the dephosphorylation of enzymes involved in redox reactions is responsible for the race-specific induced redox activity. The effects of guanidine nucleotide analogs and mastoparan on the activation of plasma membrane redox reactions support the role of GTP-binding proteins in the transduction of signals leading to the activation of the defense response mechanisms of tomato against fungal pathogens.     

Epigenetic Regulation in Plant Responses to the Environment

In this article, we review environmentally mediated epigenetic regulation in plants using two case histories. One of these, vernalization, mediates adaptation of plants to different environments and it exemplifies processes that are reset in each generation. The other, virus-induced silencing, involves transgenerationally inherited epigenetic modifications. Heritable epigenetic marks may result in heritable phenotypic variation, influencing fitness, and so be subject to natural selection. However, unlike genetic inheritance, the epigenetic modifications show instability and are influenced by the environment. These two case histories are then compared with other phenomena in plant biology that are likely to represent epigenetic regulation in response to the environment.     

Molecular Analysis of Plant Defense Responses to Plant Pathogens

A number of inducible plant responses are believed to contribute to disease resistance. These responses include the hypersensitive reaction, phytoalexin synthesis, and the production of chitinase, glucanase, and hydroxyproline-rich glycoproteins. Because of the coordinate induction of these responses, it has been difficult to determine whether they are functional defense responses, and if they are, how they specifically contribute to disease resistance. Recent developments in molecular biology have provided experimental techniques that will reveal the specific contribution of each response to disease resistance. In this paper, we describe a strategy to determine if the hypersensitive reaction is a functional plant defense mechanism.     

DNA羟甲基化与表观遗传学调控

表观遗传学中的DNA甲基化与疾病的发生发展密不可分. DNA甲基化中的5-甲基胞嘧啶易发生氧化形成5 羟甲基胞嘧啶.此过程又称为羟甲基化修饰,已成为表观遗传学研究的一种新热点.羟甲基化与10-11易位家族蛋白（ten-eleven translocation,TET）的作用密切相关,它参与了基因的表达调控以及DNA去甲基化过程. 最近的羟甲基化研究主要集中在癌症和精神性疾病.针对日趋增多的相关研究,本文对DNA羟甲基化进行了全景式综述.     

黑色素瘤发生发展中的表观遗传学调控

人恶性黑色素瘤(malignant melanoma)是近年来高发病率和高死亡率的肿瘤之一.目前尚缺乏有效的治疗方法.而表观遗传如DNA甲基化(DNA methylation)、组蛋白修饰(histonemodification)、染色质重塑(chromatin remodeling)及RNA干扰(RNA interference,RNAi)等改变在人黑色素瘤的发生、发展和转移中有重要作用.阐明黑色素瘤发生发展的表观遗传学机制已引起了学者的普遍关注.本文综述了人类黑色素瘤发生发展中所特异的表观遗传改变:CpG岛的异常甲基化修饰、组蛋白甲基化和乙酰化修饰、染色质重塑以及microRNA在黑色素瘤发生和转移中的作用,并对应用表观遗传修饰治疗人类黑色素瘤进行了探讨.     

水杨酸对水稻防卫反应酶系的系统诱导（简报）

经 10 .0 μg·ml-1水杨酸 (SA)喷雾处理后稻苗叶片中苯丙氨酸解氨酶 (PAL)、过氧化物酶 (PO)和多酚氧化酶 (PPO)活性都迅速增强 ,处理后 12～ 2 4h达到高峰。未经SA处理的叶片中PAL、PO和PPO酶活性则在处理后 4 8h达到高峰 ,且活性增加明显低于SA处理的叶片。处理和未处理叶片中木质素含量都迅速增加。这些生理指标的时序变化与SA诱导稻苗抗白叶枯病的表现基本吻合。     

Plant Defense Response to Fungal Pathogens (Activation of Host-Plasma Membrane H+-ATPase by Elicitor-Induced Enzyme Dephosphorylation)

Elicitor preparations containing the avr5 gene products from race 4 of Cladosporium fulvum and tomato (Lycopersicon esculentum L.) cells near isogenic for the resistance gene Cf5 were used to investigate events following the treatment of host plasma membranes with elicitor. A 4-fold increase in H+-ATPase activity, coincident with the acidification of the extracellular medium, was detected immediately after elicitor treatment. The elicitor-induced stimulation of the plasma membrane H+-ATPase was inhibited by okadaic acid but not by staurosporine, suggesting that protein dephosphorylation was required for increased H+-ATPase activity. This observation was confirmed by [gamma]-32P labeling and immunodetection of the plasma membrane H+-ATPase. Effects of guanidine nucleotide analogs and mastoparan on the ATPase activity suggested the role of GTP-binding proteins in mediating the putative elicitor-receptor binding, resulting in activation of a phosphatase(s), which in turn stimulates the plasma membrane H+-ATPase by dephosphorylation.     

A Rice Gene of De Novo Origin Negatively Regulates Pathogen-Induced Defense Response

How defense genes originated with the evolution of their specific pathogen-responsive traits remains an important problem. It is generally known that a form of duplication can generate new genes, suggesting that a new gene usually evolves from an ancestral gene. However, we show that a new defense gene in plants may evolve by de novo origination, resulting in sophisticated disease-resistant functions in rice. Analyses of gene evolution showed that this new gene, OsDR10, had homologs only in the closest relative, Leersia genus, but not other subfamilies of the grass family; therefore, it is a rice tribe-specific gene that may have originated de novo in the tribe. We further show that this gene may evolve a highly conservative rice-specific function that contributes to the regulation difference between rice and other plant species in response to pathogen infections. Biologic analyses including gene silencing, pathologic analysis, and mutant characterization by transformation showed that the OsDR10-suppressed plants enhanced resistance to a broad spectrum of Xanthomonas oryzae pv. oryzae strains, which cause bacterial blight disease. This enhanced disease resistance was accompanied by increased accumulation of endogenous salicylic acid (SA) and suppressed accumulation of endogenous jasmonic acid (JA) as well as modified expression of a subset of defense-responsive genes functioning both upstream and downstream of SA and JA. These data and analyses provide fresh insights into the new biologic and evolutionary processes of a de novo gene recruited rapidly.