Instituto de Biología Molecular y Celular de Plantas (IBMCP), CSIC-UPV, Valencia, Spain.
PLoS Genet. 2011 Dec;7(12):e1002434. doi: 10.1371/journal.pgen.1002434. Epub 2011 Dec 29.
RNA-directed DNA methylation (RdDM) is an epigenetic control mechanism driven by small interfering RNAs (siRNAs) that influence gene function. In plants, little is known of the involvement of the RdDM pathway in regulating traits related to immune responses. In a genetic screen designed to reveal factors regulating immunity in Arabidopsis thaliana, we identified NRPD2 as the OVEREXPRESSOR OF CATIONIC PEROXIDASE 1 (OCP1). NRPD2 encodes the second largest subunit of the plant-specific RNA Polymerases IV and V (Pol IV and Pol V), which are crucial for the RdDM pathway. The ocp1 and nrpd2 mutants showed increases in disease susceptibility when confronted with the necrotrophic fungal pathogens Botrytis cinerea and Plectosphaerella cucumerina. Studies were extended to other mutants affected in different steps of the RdDM pathway, such as nrpd1, nrpe1, ago4, drd1, rdr2, and drm1drm2 mutants. Our results indicate that all the mutants studied, with the exception of nrpd1, phenocopy the nrpd2 mutants; and they suggest that, while Pol V complex is required for plant immunity, Pol IV appears dispensable. Moreover, Pol V defective mutants, but not Pol IV mutants, show enhanced disease resistance towards the bacterial pathogen Pseudomonas syringae DC3000. Interestingly, salicylic acid (SA)-mediated defenses effective against PsDC3000 are enhanced in Pol V defective mutants, whereas jasmonic acid (JA)-mediated defenses that protect against fungi are reduced. Chromatin immunoprecipitation analysis revealed that, through differential histone modifications, SA-related defense genes are poised for enhanced activation in Pol V defective mutants and provide clues for understanding the regulation of gene priming during defense. Our results highlight the importance of epigenetic control as an additional layer of complexity in the regulation of plant immunity and point towards multiple components of the RdDM pathway being involved in plant immunity based on genetic evidence, but whether this is a direct or indirect effect on disease-related genes is unclear.
RNA 指导的 DNA 甲基化 (RdDM) 是一种由小干扰 RNA (siRNA) 驱动的表观遗传调控机制，影响基因功能。在植物中，人们对 RdDM 途径在调节与免疫反应相关的性状方面的参与知之甚少。在一项旨在揭示调控拟南芥免疫的因素的遗传筛选中，我们鉴定出 NRPD2 是阳离子过氧化物酶 1 (OCP1) 的过表达子。NRPD2 编码植物特异性 RNA 聚合酶 IV 和 V (Pol IV 和 Pol V) 的第二大亚基，这对于 RdDM 途径至关重要。ocp1 和 nrpd2 突变体在面对坏死真菌病原体 Botrytis cinerea 和 Plectosphaerella cucumerina 时，易感性增加。研究扩展到其他在 RdDM 途径的不同步骤中受到影响的突变体，如 nrpd1、nrpe1、ago4、drd1、rdr2 和 drm1drm2 突变体。我们的结果表明，除了 nrpd1 之外，所有研究的突变体都表现出与 nrpd2 突变体相似的表型；这表明 Pol V 复合物是植物免疫所必需的，而 Pol IV 似乎是可有可无的。此外，Pol V 缺陷突变体，但不是 Pol IV 突变体，对细菌病原体丁香假单胞菌 DC3000 表现出增强的抗病性。有趣的是，在 Pol V 缺陷突变体中，水杨酸 (SA) 介导的防御作用增强，而对真菌有效的茉莉酸 (JA) 介导的防御作用减弱。染色质免疫沉淀分析显示，通过差异组蛋白修饰，SA 相关防御基因在 Pol V 缺陷突变体中处于增强激活的状态，为理解防御过程中基因启动的调控提供了线索。我们的结果强调了表观遗传调控作为植物免疫调控的一个额外复杂性层次的重要性，并指出 RdDM 途径的多个成分基于遗传证据参与植物免疫，但这是否是对与疾病相关的基因的直接或间接影响尚不清楚。
