拟南芥去泛素化酶UBP12/UBP13调控RRS1/RPS4胞内免疫受体复合物的分子机制

植物胞内免疫受体NLRs作为免疫系统的重要组分，在体内稳态平衡必须受到精密调控，以防止免疫反应不能有效的激活或过度激活。泛素化和去泛素化的动态平衡作为维持蛋白质稳态的重要机制，在NLRs蛋白静息状态和激活状态下如何调节其稳定性尚不完全清楚。为了回答这个问题，申请人以拟南芥RRS1/RPS4免疫受体复合物为模型，建立了一个雌二醇化学诱导激活型RRS1/RPS4免疫反应体系。同时基于TurboID蛋白质邻近标记技术鉴定出两个去泛素化酶UBP12/UBP13为RRS1/RPS4的邻近蛋白，暗示RRS1/RPS4可能是其底物。本项目将对UBP12/UBP13如何去泛素化调控RRS1/RPS4的功能，进而影响ETI免疫反应的机理进行研究；同时阐明RRS1/RPS4在静息和激活状态下的泛素化水平和蛋白稳定性差异。研究结果可望为NLRs蛋白在免疫应答过程中的稳态调控提供理论依据。

Plant intracellular immune receptors, also known as Nucleotide-binding, Leucine-rich repeat Receptors (NLRs), are the most important part of the immune system. Proper control of NLRs protein homeostasis is critical, as over-accumulation of NLRs can lead to autoimmunity, whereas insufficient accumulation may result in compromised immune responses. The dynamic balance between ubiquitination and deubiquitination is essential for maintaining protein homeostasis. However, the exact mechanisms of how the homeostasis of NLRs controlled by ubiquitination and deubiquitination between the resting and the active states are not fully understood. We took the Arabidopsis paired NLR immune receptors complex, RRS1/RPS4, as a model system to address this question. We first generated an Arabidopsis transgenic line with estradiol-inducible expression of the effector AvrRps4 stacked with epitope-tagged RRS1 and RPS4 to activate RRS1/RPS4-mediated ETI under the control of estradiol treatment. We have identified UBP12/UBP13 as the proximal protein of RRS1/RPS4 using TurboID-based proximity labeling coupled with proteomic analysis, suggesting that RRS1/RPS4 might be deubiquitinated by UBP12/UBP13. We will further investigate the exact mechanisms by which UBP12/UBP13 deubiquitinate RRS1/RPS4 and subsequently affect the ETI immune response. We will also study how protein stability and ubiquitination pattern of RRS1/RPS4 change between the inactive and the active states. This study aims to provide new insights into the understanding of the mechanisms underlying NLRs regulation.