Characterization of the Roles of SGT1/RAR1, EDS1/NDR1, NPR1, and NRC/ADR1/NRG1 in Sw-5b-Mediated Resistance to Tomato Spotted Wilt Virus

Abstract

The tomato Sw-5b gene confers resistance to tomato spotted wilt virus (TSWV) and encodes a nucleotide-binding leucine-rich repeat (NLR) protein with an N-terminal Solanaceae-specific domain (SD). Although our understanding of how Sw-5b recognizes the viral NSm elicitor has increased significantly, the process by which Sw-5b activates downstream defense signaling remains to be elucidated. In this study, we used a tobacco rattle virus (TRV)-based virus-induced gene silencing (VIGS) system to investigate the roles of the SGT1/RAR1, EDS1/NDR1, NPR1, and NRC/ADR1/NRG1 genes in the Sw-5b-mediated signaling pathway. We found that chaperone SGT1 was required for Sw-5b function, but co-chaperone RAR1 was not. Sw-5b-mediated immune signaling was independent of both EDS1 and NDR1. Silencing NPR1, which is a central component in SA signaling, did not result in TSWV systemic infection in Sw-5b-transgenic N. benthamiana plants. Helper NLR NRCs (NLRs required for cell death) were required for Sw-5b-mediated systemic resistance to TSWV infection. Suppression of NRC2/3/4 compromised the Sw-5b resistance. However, the helper NLRs ADR1 and NRG1 may not participate in the Sw-5b signaling pathway. Silencing ADR1, NRG1, or both genes did not affect Sw-5b-mediated resistance to TSWV. Our findings provide new insight into the requirement for conserved key components in Sw-5b-mediated signaling pathways.

Evaluate the guide RNA effectiveness via Agrobacterium-mediated transient assays in Nicotiana benthamiana

“…NbNDR1 is required for the Rps2 (resistance to P . syringae )/AvrRpt2-mediated disease resistance ( Century et al., 1995 ; Aarts et al., 1998 ; Knepper et al., 2011 ; Chen et al., 2021b ). Therefore, we also inoculated pCas9- NbEDS1 / NbNDR1 gRNA transgenic plants, along with wild-type controls, with Agrobacterium tumefaciens strains carrying the 35S:: RPS2 and 35S:: avrRpt2 .…”

“…All tested transgenic plants, but not the wild-type plants, were susceptible to the infection of Xe85-10, resulting in an apparent water-soaking phenotype at the inoculation sites (Figure S2D). NbNDR1 is required for the Rps2 (resistance to P. syringae)/ AvrRpt2-mediated disease resistance (Century et al, 1995;Aarts et al, 1998;Knepper et al, 2011;Chen et al, 2021b). Therefore, we also inoculated pCas9-NbEDS1/NbNDR1 gRNA transgenic plants, along with wild-type controls, with Agrobacterium tumefaciens strains carrying the 35S::RPS2 and 35S::avrRpt2.…”

NLR we there yet? Nucleocytoplasmic coordination of NLR‐mediated immunity

“…Whereas exclusively nuclear Sw5b can restrict intercellular viral movement, the cytoplasmic pool is required for the induction of a cell death response that restricts viral replication (H. Chen et al ., 2021). Whether Sw5b interacts with transcriptional regulators inside the nucleus for defence gene induction that leads to a restriction of viral movement is unknown, but the dependency of Sw5b‐mediated viral resistance on the NRC‐helpers NRC2/3/4 has recently been revealed (Wu et al ., 2017; Z. Chen et al ., 2021).…”

Natural Resources Resistance to Tomato Spotted Wilt Virus (TSWV) in Tomato (Solanum lycopersicum)

“…Sw-5b is automatically activated (Figure 5c), and HR is triggered; these processes lead to a robust defense response against tospoviruses [33,47,71,107,108]. The phytohormones salicylic acid (SA), jasmonate (JA), ethylene (ET), and abscisic acid (ABA) play significant roles in PTI and ETI and activate the systemic acquired resistance of plants [109][110][111][112]. The SA signaling pathway has a key role in basal defense against the TSWV in tomato plants [38,113].…”