探討 NbSIR2 在圓葉菸草對疫病菌 ParA1 elicitin 反應中的角色

Abstract

被微生物侵染時，植物藉由 pattern-recognition receptors (PRRs) 辨識 microbial-associated molecular patterns (MAMPs) 或植物結構被微生物分解後的 damage-associated molecular patterns (DAMPs) 引發 pattern-triggered immunity (PTI)。根據是否含有 kinase domain，PRRs 被分為 receptor-like kinase (RLKs) 和 receptor-like proteins (RLPs)。SOBIR1 (Suppressor of BIR1-1) 是許多 RLP 型 PRRs 啟動植物防禦反應時重要的 adaptor kinase，也被證實參與植物辨識卵菌 elicitins 的過程。先前的研究藉由蛋白免疫沉澱和液相層析串聯質譜分析在圓葉菸草 (Nicotiana benthamiana) 發現多個可能與 SlSOBIR1 具有交互作用的蛋白，本研究深入探討其中一個基因 (定名為N. benthamiana SOBIR1-interacting RLP 2；NbSIR2) 的特性。NbSIR2 包含 817 個胺基酸，具備 signal peptide、leucine rich repeat (LRR) domain，以及穿膜區 (transmembrane domain, TMD) 等保守性構造；穿膜區後還有一小段 cytoplasmic tail。接種疫病菌後，NbSIR2 的表現量顯著上升，並且過表現 NbSIR2 加劇疫病菌 elicitin ParA1 引發的細胞壞疽。蛋白共免疫沉澱實驗證實了 NbSIR2 與 NbSOBIR1 存在交互作用，共軛焦螢光顯微鏡觀察與序列分析結合推斷 NbSIR2 位於植物細胞內質網膜上。SOBIR1 是植物免疫反應的一個關鍵點，本研究對 SOBIR1 調控之免疫反應提供新的研究視野，同時也為植物內質網膜蛋白參與植物的免疫反應提供新的研究方向，其中有更多機制亟待瞭解。

When infected by microbial pathogens, plants recognize microbial-associated molecular patterns (MAMPs) or plant-derived damage-associated molecular patterns (DAMPs) through pattern-recognition receptors (PRRs). Depending on the protein structure, PRRs are classified into receptor-like kinase (RLKs) and receptor-like proteins (RLPs), which differ only in the presence of C-terminal kinase domains for RLKs. SOBIR1 (suppressor of BIR1-1) has been identified as an adaptor kinase for various PRRs of the RLP type. As well, it is involved in plant response toward elicitins of Phytophthora, including ParA1 from Phytophthora parasitica. Previous studies based on co-immunoprecipitation coupled by liquid chromatography-tandem mass spectrometry (LC-MS/MS) identified various Nicotiana benthamiana proteins which might interact with SlSOBIR1. In this study, one of these genes, named SOBIR1-interacting N. benthamiana RLP2 (NbSIR2) was characterized for its role in plant response to ParA1. The expression of NbSIR2 is induced upon P. parasitica infection and NbSIR2 overexpression enhanced ParA1-induced necrosis. Co-immunoprecipitation experiment showed that NbSIR2 associated with NbSOBIR1 in planta in an elicitin-independent manner. Furthermore, analyses based on sequence prediction and confocal microscopy indicate NbSIR2 likely locates on the membrane of endoplasmic reticulum (ER). SOBIR1 plays a central role in PTI involving PRRs of the RLP type. This study introduces a new role of NbSIR2 in SOBIR1-mediated plant immunity and also helps to gain new insight into how ER membrane protein might participate in plant immunity.