NRG1 functions downstream of EDS1 to regulate TIR-NLR-mediated plant immunity in <i>Nicotiana benthamiana</i>

Abstract

Effector-triggered immunity (ETI) in plants involves a large family of nucleotide-binding leucine-rich repeat (NLR) immune receptors, including Toll/IL-1 receptor-NLRs (TNLs) and coiled-coil NLRs (CNLs). Although various NLR immune receptors are known, a mechanistic understanding of NLR function in ETI remains unclear. The TNL Recognition of XopQ 1 (Roq1) recognizes the effectors XopQ and HopQ1 from <i>Xanthomonas</i> and <i>Pseudomonas</i>, respectively, which activates resistance to <i>Xanthomonas euvesicatoria</i> and <i>Xanthomonas gardneri</i> in an Enhanced Disease Susceptibility 1 (EDS1)-dependent way in <i>Nicotiana benthamiana</i> In this study, we found that the <i>N. benthamiana</i> N requirement gene 1 (NRG1), a CNL protein required for the tobacco TNL protein N-mediated resistance to tobacco mosaic virus, is also essential for immune signaling [including hypersensitive response (HR)] triggered by the TNLs Roq1 and Recognition of <i>Peronospora parasitica</i> 1 (RPP1), but not by the CNLs Bs2 and Rps2, suggesting that NRG1 may be a conserved key component in TNL signaling pathways. Besides EDS1, Roq1 and NRG1 are necessary for resistance to <i>Xanthomonas</i> and <i>Pseudomonas</i> in <i>N. benthamiana</i> NRG1 functions downstream of Roq1 and EDS1 and physically associates with EDS1 in mediating XopQ-Roq1-triggered immunity. Moreover, RNA sequencing analysis showed that XopQ-triggered gene-expression profile changes in <i>N. benthamiana</i> were almost entirely mediated by Roq1 and EDS1 and were largely regulated by NRG1. Overall, our study demonstrates that NRG1 is a key component that acts downstream of EDS1 to mediate various TNL signaling pathways, including Roq1 and RPP1-mediated HR, resistance to <i>Xanthomonas</i> and <i>Pseudomonas</i>, and XopQ-regulated transcriptional changes in <i>N. benthamiana</i>.