Table_1_NbSOBIR1 Partitions Into Plasma Membrane Microdomains and Binds ER-Localized NbRLP1.XLSX

The receptor-like kinase Suppressor of BIR1 (SOBIR1) binds various receptor-like proteins (RLPs) that perceive microbe-associated molecular patterns (MAMPs) at the plasma membrane, which is thought to activate plant pattern-triggered immunity (PTI) against pathogen invasion. Despite its potentially crucial role, how SOBIR1 transmits immune signaling to ultimately elicit PTI remains largely unresolved. Herein, we report that a Nicotiana benthamiana gene NbRLP1, like NbSOBIR1, was highly induced upon Phytophthora parasitica infection. Intriguingly, NbRLP1 is characterized as a receptor-like protein localizing to the endoplasmic reticulum (ER) membrane rather than the plasma membrane. Using bimolecular fluorescence complementation and affinity purification assays, we established that NbRLP1 is likely to associate with NbSOBIR1 through the contact between the ER and plasma membrane. We further found that NbSOBIR1 at the plasma membrane partitions into mobile microdomains that undergo frequent lateral movement and internalization. Remarkably, the dynamics of NbSOBIR1 microdomain is coupled to the remodeling of the cortical ER network. When NbSOBIR1 microdomains were induced by the P. parasitica MAMP ParA1, tobacco cells overexpressing NbRLP1 accelerated NbSOBIR1 internalization. Overexpressing NbRLP1 in tobacco further exaggerated the ParA1-induced necrosis. Together, these findings have prompted us to propose that ER and the ER-localized NbRLP1 may play a role in transmitting plant immune signals by regulating NbSOBIR1 internalization.

受体样激酶BIR1抑制因子（Suppressor of BIR1, SOBIR1）可结合多种在质膜处识别微生物相关分子模式（microbe-associated molecular patterns, MAMPs）的类受体蛋白（receptor-like proteins, RLPs），该过程被认为可激活植物针对病原菌侵染的模式触发免疫（pattern-triggered immunity, PTI）。尽管其潜在关键作用已被认知，但SOBIR1如何传递免疫信号以最终引发PTI的机制仍未得到充分阐明。本研究中，我们报道本氏烟草（Nicotiana benthamiana）基因NbRLP1与NbSOBIR1类似，在寄生疫霉（Phytophthora parasitica）侵染后表达量显著上调。有趣的是，NbRLP1被鉴定为定位于内质网（endoplasmic reticulum, ER）膜而非质膜的类受体蛋白。通过双分子荧光互补（bimolecular fluorescence complementation）与亲和纯化实验（affinity purification assays），我们证实NbRLP1可能通过内质网与质膜的接触位点与NbSOBIR1发生相互作用。我们进一步发现，质膜上的NbSOBIR1可聚集形成可移动的微结构域，这些微结构域会发生频繁的侧向运动与内吞作用。值得注意的是，NbSOBIR1微结构域的动态变化与皮层内质网网络（cortical ER network）的重塑相耦合。当寄生疫霉来源的MAMP ParA1诱导NbSOBIR1微结构域形成时，过表达NbRLP1的烟草细胞会加速NbSOBIR1的内吞过程。在烟草中过表达NbRLP1还会加剧ParA1诱导的细胞坏死。综上，上述研究结果促使我们提出如下假说：内质网及其定位于内质网的NbRLP1可能通过调控NbSOBIR1的内吞过程参与植物免疫信号的传递。