A plant NLR receptor activates auxin signaling through Aux/IAAs-ARF19 and YUC8-TIR1/AFBs to promote callose-mediated antiviral defense

Phytohormone signaling pathways are crucial for defense against pathogens mediated by pattern recognition receptors and nucleotide-binding leucine-rich repeat (NLR) immune receptors. The induction of auxin signaling by immune receptors for antiviral immunity is poorly understood despite its notable role in plant defense against viral pathogens. Here, we report that plant NLR Sw-5b initiates and amplifies auxin signaling through auxin/indole-3-acetic acid (Aux/IAAs)-ARF19 and YUC8-transport inhibitor response1/auxin-signaling F-box (TIR1/AFB) modules to promote callose-mediated antiviral defense. Upon recognizing viral effector, Sw-5b associates with and relieves repressors Aux/IAAs on transcription factor ARF19. ARF19 then activates callose synthase gene <i>GSL5/8</i> to deposit callose at plasmodesmata, inhibiting viral cell-to-cell spread. Meanwhile, ARF19 activates auxin biosynthesis gene <i>YUC8</i> to boost auxin production; this further amplifies callose deposition signaling via TIR1/AFB receptors and Aux/IAAs-ARF19-glucan synthase-like (GSL) module, thereby restricting the virus in localized cell death. Our findings provide valuable insights into the mechanism by which plant immune receptors induce phytohormone signaling pathways to combat pathogens.