He K, Wu Y
Ministry of Education Key Laboratory of Cell Activities and Stress Adaptations, School of Life Sciences, Lanzhou University, Lanzhou, China.
Ministry of Education Key Laboratory of Cell Activities and Stress Adaptations, School of Life Sciences, Lanzhou University, Lanzhou, China.
Enzymes. 2016;40:105-142. doi: 10.1016/bs.enz.2016.09.003. Epub 2016 Oct 5.
Plants are sessile organisms exposed constantly to potential virulent microbes seeking for full pathogenesis in hosts. Different from animals employing both adaptive and innate immune systems, plants only rely on innate immunity to detect and fight against pathogen invasions. Plant innate immunity is proposed to be a two-tiered immune system including pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI) and effector-triggered immunity. In PTI, PAMPs, the elicitors derived from microbial pathogens, are perceived by cell surface-localized proteins, known as pattern recognition receptors (PRRs), including receptor-like kinases (RLKs) and receptor-like proteins (RLPs). As single-pass transmembrane proteins, RLKs and RLPs contain an extracellular domain (ECD) responsible for ligand binding. Recognitions of signal molecules by PRR-ECDs induce homo- or heterooligomerization of RLKs and RLPs to trigger corresponding intracellular immune responses. RLKs possess a cytoplasmic Ser/Thr kinase domain that is absent in RLPs, implying that protein phosphorylations underlie key mechanism in transducing immunity signalings and that RLPs unlikely mediate signal transduction independently, and recruitment of other patterns, such as RLKs, is required for the function of RLPs in plant immunity. Receptor-like cytoplasmic kinases, resembling RLK structures but lacking the ECD, act as immediate substrates of PRRs, modulating PRR activities and linking PRRs with downstream signaling mediators. In this chapter, we summarize recent discoveries illustrating the molecular machines of major components of PRR complexes in mediating pathogen perception and immunity activation in plants.
植物是固着生物，不断暴露于寻求在宿主中实现完全致病的潜在致病微生物面前。与同时采用适应性免疫系统和先天性免疫系统的动物不同，植物仅依靠先天性免疫来检测和对抗病原体入侵。植物先天性免疫被认为是一种双层免疫系统，包括病原体相关分子模式（PAMP）触发的免疫（PTI）和效应子触发的免疫。在PTI中，源自微生物病原体的激发子PAMPs被细胞表面定位的蛋白质感知，这些蛋白质被称为模式识别受体（PRR），包括受体样激酶（RLK）和受体样蛋白（RLP）。作为单次跨膜蛋白，RLK和RLP包含负责配体结合的细胞外结构域（ECD）。PRR-ECD对信号分子的识别诱导RLK和RLP的同源或异源寡聚化，以触发相应的细胞内免疫反应。RLK具有RLP中不存在的细胞质丝氨酸/苏氨酸激酶结构域，这意味着蛋白质磷酸化是转导免疫信号的关键机制，并且RLP不太可能独立介导信号转导，RLP在植物免疫中的功能需要招募其他模式，如RLK。受体样细胞质激酶，类似于RLK结构但缺乏ECD，作为PRR的直接底物，调节PRR活性并将PRR与下游信号介质联系起来。在本章中，我们总结了最近的发现，这些发现阐明了PRR复合物主要成分在介导植物病原体感知和免疫激活中的分子机制。
