Cytoplasmic and nuclear Sw-5b NLR act both independently and synergistically to confer full host defense against tospovirus infection

Plant intracellular nucleotide-binding leucine-rich repeat (NLR) receptors play critical roles in mediating host immunity to pathogen attack. We use tomato Sw-5b::tospovirus as a model system to study the specific role of the compartmentalized plant NLR in dictating host defenses against the virus at different infection steps. We demonstrated here that tomato NLR Sw-5b distributes to the cytoplasm and nucleus, respectively, to play different roles in inducing host resistances against tomato spotted wilt orthotospovirus (TSWV) infection. The cytoplasmic-enriched Sw-5b induces a strong cell death response to inhibit TSWV replication. This host response is, however, insufficient to block viral intercellular and long-distance movement. The nuclear-enriched Sw-5b triggers a host defense that weakly inhibits viral replication but strongly impedes virus intercellular and systemic movement. Furthermore, the cytoplasmic and nuclear Sw-5b act synergistically to dictate a full host defense of TSWV infection. We further demonstrated that the extended N-terminal Solanaceae domain (SD) of Sw-5b plays critical roles in cytoplasm/nucleus partitioning. Sw-5b NLR controls its cytoplasm localization. Strikingly, the SD but not coil-coil domain is crucial for Sw-5b receptor to import into the nucleus to trigger the immunity. The SD was found to interact with importins. Silencing both importin alpha and beta expression disrupted Sw-5b nucleus import and host immunity against TSWV systemic infection. Collectively, our findings suggest that Sw-5b bifurcates disease resistances by cytoplasm/nucleus partitioning to block different infection steps of TSWV. The findings also identified a new regulatory role of extra domain of a plant NLR in mediating host innate immunity.

植物细胞内的核苷酸结合富亮氨酸重复序列（NLR）受体在介导宿主对病原体侵袭的免疫中起关键作用。我们以番茄Sw - 5b::番茄斑萎病毒属病毒作为模型系统，研究区室化植物NLR在决定宿主针对病毒不同感染阶段的防御中所起的特定作用。在此我们证明，番茄NLR Sw - 5b分别分布于细胞质和细胞核，在诱导宿主对番茄斑萎正番茄斑萎病毒（TSWV）感染的抗性中发挥不同作用。富集于细胞质的Sw - 5b诱导强烈的细胞死亡反应以抑制TSWV复制。然而，这种宿主反应不足以阻断病毒的细胞间和长距离移动。富集于细胞核的Sw - 5b触发一种宿主防御，该防御对病毒复制的抑制作用较弱，但对病毒的细胞间和系统移动有强烈阻碍作用。此外，细胞质和细胞核中的Sw - 5b协同作用，决定了对TSWV感染的全面宿主防御。我们进一步证明，Sw - 5b的延伸的N末端茄科结构域（SD）在细胞质/细胞核分配中起关键作用。Sw - 5b NLR控制其细胞质定位。引人注目的是，SD而非卷曲螺旋结构域对于Sw - 5b受体进入细胞核以触发免疫至关重要。发现SD与输入蛋白相互作用。沉默输入蛋白α和β的表达会破坏Sw - 5b进入细胞核以及宿主对TSWV系统感染的免疫。总之，我们的研究结果表明，Sw - 5b通过细胞质/细胞核分配来分化抗病性，以阻断TSWV的不同感染阶段。这些发现还确定了植物NLR的额外结构域在介导宿主先天免疫中的一种新的调控作用。