The rice NLR pair Pikp-1/Pikp-2 initiates cell death through receptor cooperation rather than negative regulation
The rice NLR pair Pikp-1/Pikp-2 initiates cell death through receptor cooperation rather than negative regulation
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DOI：
10.1101/2020.06.20.162834
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发表时间：
2020-06
期刊：
影响因子：
3.7
通讯作者：
Rafał Zdrzałek;S. Kamoun;R. Terauchi;H. Saitoh;M. Banfield
中科院分区：
文献类型：
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作者：
Rafał Zdrzałek;S. Kamoun;R. Terauchi;H. Saitoh;M. Banfield
植物NLR免疫受体是多结构域蛋白，可以作为专门的传感器/辅助对发挥作用。成对的NLR免疫受体通常被认为通过负调节发挥作用，其中一个NLR抑制第二个NLR的活性，并且病原体效应物的检测解除这种抑制以启动免疫。然而，这种机制是否是共同的所有NLR对是未知的。在这里，我们表明，水稻NLR对Pikp-1/Pikp-2，赋予抗稻瘟病病原体稻瘟病菌菌株（syn.表达AVR-PikD效应子的梨孢霉（Pyricularia）通过受体合作发挥功能，其中效应子触发的激活需要两个NLR来触发免疫应答。为了研究Pikp-1/Pikp-2激活的机制，我们表达了这些蛋白质的截短变体，并在先前鉴定的NLR序列基序中进行突变。我们发现，在Pikp-1或Pikp-2中的任何结构域截短都可以防止AVR-PikD存在下的细胞死亡，这表明所有结构域都是活性所必需的。此外，单个Pikp-1或Pikp-2结构域的表达不会导致细胞死亡。Pikp-1和Pikp-2中保守的P环和MHD序列基序的突变阻止了细胞死亡激活，表明这些基序是两个伴侣NLR功能所必需的。最后，我们表明，Pikp-1和Pikp-2协会形成同源和异源复合物在植物中的AVR-PikD的情况下，在共表达的效应器结合到Pikp-1产生三重复合物。总而言之，我们提供了证据表明Pikp-1和Pikp-2形成了一个微调系统，该系统通过受体合作而不是负调节被AVR-PikD激活。
Plant NLR immune receptors are multidomain proteins that can function as specialized sensor/helper pairs. Paired NLR immune receptors are generally thought to function via negative regulation, where one NLR represses the activity of the second and detection of pathogen effectors relieves this repression to initiate immunity. However, whether this mechanism is common to all NLR pairs is not known. Here, we show that the rice NLR pair Pikp-1/Pikp-2, which confers resistance to strains of the blast pathogen Magnaporthe oryzae (syn. Pyricularia oryzae) expressing the AVR-PikD effector, functions via receptor cooperation, with effector-triggered activation requiring both NLRs to trigger the immune response. To investigate the mechanism of Pikp-1/Pikp-2 activation, we expressed truncated variants of these proteins, and made mutations in previously identified NLR sequence motifs. We found that any domain truncation, in either Pikp-1 or Pikp-2, prevented cell death in the presence of AVR-PikD, revealing that all domains are required for activity. Further, expression of individual Pikp-1 or Pikp-2 domains did not result in cell death. Mutations in the conserved P-loop and MHD sequence motifs in both Pikp-1 and Pikp-2 prevented cell death activation, demonstrating that these motifs are required for the function of the two partner NLRs. Finally, we showed that Pikp-1 and Pikp-2 associate to form homo- and hetero-complexes in planta in the absence of AVR-PikD; on co-expression the effector binds to Pikp-1 generating a tripartite complex. Taken together, we provide evidence that Pikp-1 and Pikp-2 form a fine-tuned system that is activated by AVR-PikD via receptor cooperation rather than negative regulation.