Two Prp19-like U-box proteins in the MOS4-associated complex play redundant roles in plant innate immunity.
Two Prp19-like U-box proteins in the MOS4-associated complex play redundant roles in plant innate immunity.
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DOI：
10.1371/journal.ppat.1000526
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发表时间：
2009-07
期刊：
影响因子：
6.7
通讯作者：
Li X
中科院分区：
文献类型：
--
作者：
Monaghan J;Xu F;Gao M;Zhao Q;Palma K;Long C;Chen S;Zhang Y;Li X
植物抗性(R)蛋白在抵御病原菌侵染中发挥着不可或缺的作用。R基因SNc1是一种独特的功能获得性突变，它导致植物免疫途径的结构性激活和对病原菌侵染的抗性增强。我们先前发现MOS4的突变抑制了SNc1的自身免疫表型，并且MOS4是称为MOS4相关复合体(MAC)的核复合体的一部分，与转录因子AtCDC5和WD-40蛋白PRL1一起。在这里，我们报道了用HA标记的MOS4对MAC进行免疫亲和纯化，然后用质谱仪进行蛋白质序列分析。总共鉴定了24个MAC蛋白，其中19个根据它们与Prp19-复合体中蛋白质的同源性预测了它们在RNA加工中的作用。Prp19-复合体是一种进化上保守的剪接体相关复合体，包含MOS4、AtCDC5和PRL1的同源物。其中有两个与酵母高度相似的U-box蛋白和人类E3泛素连接酶Prp19，我们将其命名为MAC3A和MAC3B。最近发现MAC3B在体外具有E3连接酶活性。通过反向遗传学分析，我们发现MAC3A和MAC3B在功能上是冗余的，是拟南芥基础蛋白和R蛋白介导的抗性所必需的。与Mos4-1和Atcdc5-1一样，mac3a mac3b抑制SNc1介导的自身免疫。Mac3定位于细胞核，并在PlantA与AtCDC5相互作用。我们的结果表明，MAC3A和MAC3B是在植物天然免疫调节中冗余功能的MAC成员。植物已经进化出复杂的机制来感知和响应病原体的感染。一种强大的防御反应是由抗性(R)蛋白介导的，这些蛋白识别特定的病原体衍生的效应器分子，并在受感染的细胞中启动信号级联反应，以阻止病原体的生长。通过利用防御反应改变的突变体，可以研究参与植物免疫的遗传途径。利用模式植物拟南芥，我们以前在一个称为MOS4相关复合体(MAC)的复合体中鉴定了三种蛋白质，它们是植物免疫反应所必需的，并且在从酵母到人类的真核生物中高度保守。我们有兴趣进一步研究这种蛋白质复合体在植物中的作用。在这里，我们报道了MAC的提纯和其成分的鉴定。我们进一步详细鉴定了两个高度相似的MAC蛋白，我们称之为MAC3A和MAC3B。这些蛋白质在功能上是多余的，是对几种病原体做出有效抗性反应所必需的。我们的证据表明，MAC代表着植物抗病的关键调控节点。
Plant Resistance (R) proteins play an integral role in defense against pathogen infection. A unique gain-of-function mutation in the R gene SNC1, snc1, results in constitutive activation of plant immune pathways and enhanced resistance against pathogen infection. We previously found that mutations in MOS4 suppress the autoimmune phenotypes of snc1, and that MOS4 is part of a nuclear complex called the MOS4-Associated Complex (MAC) along with the transcription factor AtCDC5 and the WD-40 protein PRL1. Here we report the immuno-affinity purification of the MAC using HA-tagged MOS4 followed by protein sequence analysis by mass spectrometry. A total of 24 MAC proteins were identified, 19 of which have predicted roles in RNA processing based on their homology to proteins in the Prp19-Complex, an evolutionarily conserved spliceosome-associated complex containing homologs of MOS4, AtCDC5, and PRL1. Among these were two highly similar U-box proteins with homology to the yeast and human E3 ubiquitin ligase Prp19, which we named MAC3A and MAC3B. MAC3B was recently shown to exhibit E3 ligase activity in vitro. Through reverse genetics analysis we show that MAC3A and MAC3B are functionally redundant and are required for basal and R protein–mediated resistance in Arabidopsis. Like mos4-1 and Atcdc5-1, mac3a mac3b suppresses snc1-mediated autoimmunity. MAC3 localizes to the nucleus and interacts with AtCDC5 in planta. Our results suggest that MAC3A and MAC3B are members of the MAC that function redundantly in the regulation of plant innate immunity. Plants have evolved sophisticated mechanisms to sense and respond to pathogen infection. One robust defense response is mediated by Resistance (R) proteins that recognize specific pathogen-derived effector molecules and initiate signaling cascades in the infected cells to impede pathogen growth. By using mutants with altered defense responses, genetic pathways involved in plant immunity can be studied. Using the model plant Arabidopsis thaliana, we previously characterized three proteins in a complex called the MOS4-Associated Complex (MAC) that are integral to plant immune responses and are highly conserved among eukaryotes from yeast to human. We were interested in further studying the role of this protein complex in plants. Here, we report the purification of the MAC and the identification of its components. We further characterized two highly similar MAC proteins in detail, which we called MAC3A and MAC3B. These proteins are functionally redundant and are required for effective resistance responses to several pathogens. Our evidence suggests that the MAC represents a key regulatory node for plant disease resistance.
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