Effector-Triggered Immunity Is a Key Component of Nonhost Resistance in Nicotiana benthamiana against the Rice Blast Pathogen Magnaporthe oryzae.

Abstract

Magnaporthe oryzae is the causal agent of rice blast disease, a major threat to global food security. Although M. oryzae infects a broad range of monocotyledonous plants, it fails to colonize dicot species such as Nicotiana benthamiana, offering a useful system to investigate nonhost resistance (NHR). In this study, we characterized the immune responses of N. benthamiana to M. oryzae by profiling defense-related gene expression, analyzing fungal invasion, and functionally dissecting key immune components. Time-course expression analyses revealed sustained upregulation of NbBAK1, NbEAS, NbWRKY22, and NbPR1, alongside dynamic regulation of NbCYP71D20 and NbSGT1. Virus-induced gene silencing demonstrated that silencing of NbSGT1, but not NbEAS or NbBAK1, significantly enhanced fungal colonization. Furthermore, salicylic acid (SA)-deficient NahG plants exhibited increased susceptibility, suggesting that SA and SGT1-dependent immunity synergistically contribute to NHR. Visualization of infection using a GFP-expressing fungal strain confirmed that suppression of SGT1 and SA signaling facilitated hyphal expansion into adjacent host cells. High-throughput screening of 179 M. oryzae candidate effectors revealed that 70 induced hypersensitive response-like cell death in N. benthamiana, a response that was abrogated by NbSGT1 silencing. These findings collectively demonstrate that SA signaling and SGT1-dependent effector-triggered immunity are critical barriers against M. oryzae invasion and highlight the potential of nonhost immune components as resources for engineering durable resistance in crops.