Department of Biology, University of North Carolina, Chapel Hill, North Carolina, USA.
PLoS Genet. 2013;9(4):e1003465. doi: 10.1371/journal.pgen.1003465. Epub 2013 Apr 25.
Plants react to pathogen attack via recognition of, and response to, pathogen-specific molecules at the cell surface and inside the cell. Pathogen effectors (virulence factors) are monitored by intracellular nucleotide-binding leucine-rich repeat (NB-LRR) sensor proteins in plants and mammals. Here, we study the genetic requirements for defense responses of an autoactive mutant of ADR1-L2, an Arabidopsis coiled-coil (CC)-NB-LRR protein. ADR1-L2 functions upstream of salicylic acid (SA) accumulation in several defense contexts, and it can act in this context as a "helper" to transduce specific microbial activation signals from "sensor" NB-LRRs. This helper activity does not require an intact P-loop. ADR1-L2 and another of two closely related members of this small NB-LRR family are also required for propagation of unregulated runaway cell death (rcd) in an lsd1 mutant. We demonstrate here that, in this particular context, ADR1-L2 function is P-loop dependent. We generated an autoactive missense mutation, ADR1-L2D484V, in a small homology motif termed MHD. Expression of ADR1-L2D848V leads to dwarfed plants that exhibit increased disease resistance and constitutively high SA levels. The morphological phenotype also requires an intact P-loop, suggesting that these ADR1-L2D484V phenotypes reflect canonical activation of this NB-LRR protein. We used ADR1-L2D484V to define genetic requirements for signaling. Signaling from ADR1-L2D484V does not require NADPH oxidase and is negatively regulated by EDS1 and AtMC1. Transcriptional regulation of ADR1-L2D484V is correlated with its phenotypic outputs; these outputs are both SA-dependent and -independent. The genetic requirements for ADR1-L2D484V activity resemble those that regulate an SA-gradient-dependent signal amplification of defense and cell death signaling initially observed in the absence of LSD1. Importantly, ADR1-L2D484V autoactivation signaling is controlled by both EDS1 and SA in separable, but linked pathways. These data allows us to propose a genetic model that provides insight into an SA-dependent feedback regulation loop, which, surprisingly, includes ADR1-L2.
植物通过在细胞表面和细胞内识别和响应病原体特异性分子来对病原体攻击做出反应。病原体效应子（毒力因子）被植物和哺乳动物中的细胞内核苷酸结合亮氨酸丰富重复（NB-LRR）传感器蛋白监测。在这里，我们研究了 ADR1-L2 自动激活突变体防御反应的遗传要求，ADR1-L2 是拟南芥卷曲螺旋（CC）-NB-LRR 蛋白。ADR1-L2 在几种防御情况下在水杨酸（SA）积累之前起作用，并且它可以在这种情况下作为“辅助因子”从“传感器”NB-LRR 传递特定微生物激活信号。这种辅助活性不需要完整的 P 环。ADR1-L2 和这个小的 NB-LRR 家族的另外两个密切相关的成员也需要在 lsd1 突变体中传播不受调节的失控细胞死亡（rcd）。我们在这里证明，在这种特殊情况下，ADR1-L2 的功能依赖于 P 环。我们在一个称为 MHD 的小同源基序中生成了一个自动激活的错义突变 ADR1-L2D484V。ADR1-L2D848V 的表达导致矮化植物，表现出增强的抗病性和持续高水平的 SA。形态表型还需要一个完整的 P 环，这表明这些 ADR1-L2D484V 表型反映了该 NB-LRR 蛋白的典型激活。我们使用 ADR1-L2D484V 来定义信号转导的遗传要求。来自 ADR1-L2D484V 的信号转导不需要 NADPH 氧化酶，并且受到 EDS1 和 AtMC1 的负调控。ADR1-L2D484V 的转录调控与表型输出相关；这些输出既依赖于 SA 又不依赖于 SA。ADR1-L2D484V 活性的遗传要求类似于那些调节最初在没有 LSD1 的情况下观察到的防御和细胞死亡信号的 SA 依赖性信号放大的要求。重要的是，ADR1-L2D484V 自动激活信号转导受到 EDS1 和 SA 的控制，这两种信号转导途径在可分离但相关的途径中受到控制。这些数据使我们能够提出一个遗传模型，该模型深入了解 SA 依赖性反馈调节回路，令人惊讶的是，该回路包括 ADR1-L2。
