Structure Analysis Uncovers a Highly Diverse but Structurally Conserved Effector Family in Phytopathogenic Fungi.
Structure Analysis Uncovers a Highly Diverse but Structurally Conserved Effector Family in Phytopathogenic Fungi.
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DOI：
10.1371/journal.ppat.1005228
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发表时间：
2015-10
期刊：
影响因子：
6.7
通讯作者：
Padilla A
中科院分区：
文献类型：
--
作者：
de Guillen K;Ortiz-Vallejo D;Gracy J;Fournier E;Kroj T;Padilla A
植物致病性子囊菌真菌具有巨大的效应库，由数百个序列无关的小分泌蛋白主导。这些效应物的分子功能和产生大量单基因的进化机制在很大程度上是未知的。为了更深入地了解真菌效应物，我们通过核磁共振光谱测定了Magnaporthe oryzae效应物AVR1-CO39和AVR-Pia的三维结构。尽管缺乏序列相似性，但这两种蛋白质都具有非常相似的6 β-三明治结构，在这两种情况下，由位于蛋白质相似位置的2个保守半胱氨酸之间的二硫桥稳定。结构相似性搜索结果显示，另一种来自M. oryzae的效应物avrpie -t和小麦黑斑病致病菌Pyrenophora tritrirepentis的效应物ToxB具有相同的结构，这表明存在一个序列无关但结构保守的真菌效应物家族，我们将其命名为max -效应物（M agnapor， Avrs和ToxB like）。结构信息模式搜索通过在广泛的子囊菌植物病原体中识别max效应候选物加强了这一假设。在M. oryzae和M. grisea中检测到max -效应物家族的强烈扩增，其中它们似乎特别重要，因为它们占效应物库的5-10%和克隆的无毒效应物的50%。表达分析表明，大部分m.o ryzae max -效应物在感染早期特异性表达，提示在生物营养寄主定植过程中具有重要功能。我们假设，观察到的max效应物的情况可以作为子囊菌效应物多样性的范例，并且大量序列无关的子囊菌效应物实际上可能属于一组结构保守的效应物家族。植物真菌病原体具有突出的经济和生态重要性，并对许多栽培和野生植物造成破坏性疾病。在感染过程中分泌的操纵宿主和促进疾病的效应蛋白是真菌毒力的关键因素。植物病原真菌具有巨大的效应库，由数百个序列无关的小分泌蛋白主导。这类最重要的真菌效应物的分子功能，以及产生大量明显不相关的蛋白质的进化机制，在很大程度上是未知的。通过研究稻瘟病菌m.o ryzae效应物的三维结构，我们发现了一个效应物家族，包括来自m.o ryzae和系统发育上遥远的小麦病原菌Pyrenophora tritri- repentis的结构保守但序列无关的效应物，我们将其命名为max效应物（m.o ryzae Avrs和ToxB）。对全基因组序列数据库的结构信息搜索表明，在许多子囊菌植物病原体中，max效应物以低频率存在，并且具有不完整的系统发育分布。它们在含有M. oryzae的pyricariae家族真菌中进行了强烈的谱系特异性扩增，在生物营养化植物定植过程中它们似乎特别重要，占克隆Avr效应物的50%和效应物库的5-10%。基于我们对max效应器的研究结果和真菌效应器根据生-死模型进化的广泛接受的概念，我们提出了一个假设，即大量不同的子囊菌效应器实际上可能属于一组有限的结构定义的家族，其成员是系统发育相关的。
Phytopathogenic ascomycete fungi possess huge effector repertoires that are dominated by hundreds of sequence-unrelated small secreted proteins. The molecular function of these effectors and the evolutionary mechanisms that generate this tremendous number of singleton genes are largely unknown. To get a deeper understanding of fungal effectors, we determined by NMR spectroscopy the 3-dimensional structures of the Magnaporthe oryzae effectors AVR1-CO39 and AVR-Pia. Despite a lack of sequence similarity, both proteins have very similar 6 β-sandwich structures that are stabilized in both cases by a disulfide bridge between 2 conserved cysteins located in similar positions of the proteins. Structural similarity searches revealed that AvrPiz-t, another effector from M. oryzae, and ToxB, an effector of the wheat tan spot pathogen Pyrenophora tritici-repentis have the same structures suggesting the existence of a family of sequence-unrelated but structurally conserved fungal effectors that we named MAX-effectors (M agnaporthe Avrs and ToxB like). Structure-informed pattern searches strengthened this hypothesis by identifying MAX-effector candidates in a broad range of ascomycete phytopathogens. Strong expansion of the MAX-effector family was detected in M. oryzae and M. grisea where they seem to be particularly important since they account for 5–10% of the effector repertoire and 50% of the cloned avirulence effectors. Expression analysis indicated that the majority of M. oryzae MAX-effectors are expressed specifically during early infection suggesting important functions during biotrophic host colonization. We hypothesize that the scenario observed for MAX-effectors can serve as a paradigm for ascomycete effector diversity and that the enormous number of sequence-unrelated ascomycete effectors may in fact belong to a restricted set of structurally conserved effector families. Fungal plant pathogens are of outstanding economic and ecological importance and cause destructive diseases on many cultivated and wild plants. Effector proteins that are secreted during infection to manipulate the host and to promote disease are a key element in fungal virulence. Phytopathogenic fungi possess huge effector repertoires that are dominated by hundreds of sequence-unrelated small secreted proteins. The molecular functions of this most important class of fungal effectors and the evolutionary mechanisms that generate this tremendous numbers of apparently unrelated proteins are largely unknown. By investigating the 3-dimensional structures of effectors from the rice blast fungus M. oryzae, we discovered an effector family comprising structurally conserved but sequence-unrelated effectors from M. oryzae and the phylogenetically distant wheat pathogen Pyrenophora tritici-repentis that we named MAX-effectors (M. oryzae Avrs and ToxB). Structure-informed searches of whole genome sequence databases suggest that MAX-effectors are present at low frequencies and with a patchy phylogenetic distribution in many ascomycete phytopathogens. They underwent strong lineage-specific expansion in fungi of the Pyriculariae family that contains M. oryzae where they seem particularly important during biotrophic plant colonization and account for 50% of the cloned Avr effectors and 5–10% of the effector repertoire. Based on our results on the MAX-effectors and the widely accepted concept that fungal effectors evolve according to a birth-and-death model we propose the hypothesis that the majority of the immense numbers of different ascomycete effectors could in fact belong to a limited set of structurally defined families whose members are phylogenetically related.