Proxitome profiling reveals a conserved SGT1-NSL1 signaling module that activates NLR-mediated immunity.

ABSTRACT

SGT1 is a highly conserved eukaryotic protein that plays a vital role in the growth, development, and immunity in both animals and plants. Although some SGT1 interactors have been identified, the molecular regulatory network of SGT1 remains unclear. SGT1 serves as a co-chaperone to stabilize protein complexes such as the nucleotide-binding leucine-rich repeat (NLR) class of immune receptors, thereby positively regulating plant immunity. SGT1 has also been found to be associated with the SKP1-Cullin-F-box (SCF) E3 ubiquitin ligase complex. However, whether SGT1 targets immune repressors to coordinate plant immune activation remains elusive. Here, we constructed a toolbox for TurboID- and split-TurboID-based proximity labeling (PL) assays in Nicotiana benthamiana. We used the PL toolbox to explore the SGT1 interactome during pre- and post-immune activation. The comprehensive SGT1 interactome network that we identified highlights a dynamic shift from proteins associated with plant development to those linked with plant immune responses. SGT1 interacts with Necrotic Spotted Lesion 1 (NSL1) that negatively regulates salicylic acid (SA)-mediated defense by interfering with the nucleocytoplasmic trafficking of Non-expressor of Pathogenesis-Related Genes 1 (NPR1) during N NLR-mediated response to tobacco mosaic virus (TMV). SGT1 promotes the SCF-dependent degradation of NSL1 to facilitate immune activation, while salicylate-induced protein kinase (SIPK)-mediated phosphorylation of SGT1 further potentiates this process. Besides N NLR, NSL1 also functions in several other NLR-mediated immunity. Our study unveils the regulatory landscape of SGT1 and reveals a novel SGT1-NSL1 signaling module that orchestrates plant innate immunity.