Arabidopsis resistance protein SNC1 activates immune responses through association with a transcriptional corepressor

Abstract

In both plants and animals, nucleotide-binding (NB) domain and leucine-rich repeat (LRR)-containing proteins (NLR) function as sensors of pathogen-derived molecules and trigger immune responses. Although NLR resistance (R) proteins were first reported as plant immune receptors more than 15 years ago, how these proteins activate downstream defense responses is still unclear. Here we report that the Toll-like/interleukin-1 receptor (TIR)-NB-LRR R protein, suppressor of npr1-1, constitutive 1 (SNC1) functions through its associated protein, Topless-related 1 (TPR1). Knocking out TPR1 and its close homologs compromises immunity mediated by SNC1 and several other TIR-NB-LRR-type R proteins, whereas overexpression of TPR1 constitutively activates SNC1-mediated immune responses. TPR1 functions as a transcriptional corepressor and associates with histone deacetylase 19 in vivo. Among the target genes of TPR1 are Defense no Death 1 (DND1) and Defense no Death 2 (DND2), two known negative regulators of immunity that are repressed during pathogen infection, suggesting that TPR1 activates R protein-mediated immune responses through repression of negative regulators.histone deacetylase 19 | plant immunity | Topless | Topless-related 1 P lant resistance (R) proteins play important roles in defense against pathogens. The majority of R proteins contain either a Toll-like/interleukin 1 receptor (TIR) or a coiled coil (CC) domain at their N terminus domain, a central nucleotide-binding (NB) domain, and C-terminal leucine-rich repeats (LRRs). Downstream components for TIR-and CC-NB-LRR R proteins appear to be different. Mutations in enhanced disease susceptibility 1 (EDS1), phytoalexin deficient 4 (PAD4), and senescence-associated gene101 (SAG101) affect the resistance specified by TIR-NB-LRR but not by CC-NB-LRR R proteins (1-3). On the other hand, mutations in non-race-specific disease resistance 1 (NDR1) compromise resistance mediated by CC-NB-LRR but not by TIR-NB-LRR R proteins (1, 4). EDS1, PAD4, and SAG101 encode three related proteins with homology to acyl hydrolases (3,5,6). How these proteins regulate R protein signaling is not clear.Increasing evidence suggests that certain R proteins accumulate in the nucleus and that the nuclear pools of these R proteins are important for the activation of defense responses (7-10). Multiple TIR-NB-LRR R proteins, including nicotiana glutinosa virus resistance protein (N) in tobacco and resistance to Pseudomonas syringae 4 (RPS4) and suppressor of npr1-1, constitutive 1 (SNC1) in Arabidopsis, have been shown to localize to the nucleus, and reduction of the nuclear R protein pool attenuates the activation of downstream defense responses (7-10). These findings are consistent with that the nucleocytoplasmic trafficking machinery is required for R protein-mediated immunity (9,11,12). However, the function of these R proteins in the nucleus and whether they participate directly or indirectly in transcriptional regulation of defense genes is unclear.Despite tremendous progress has been made ...

The JAZ Proteins: A Crucial Interface in the Jasmonate Signaling Cascade

“…The exact mechanism by which TPL restrains gene expression remains unclear. Some data point to a link with the histone deacetylase HDA19 (At4g38130; Long et al, 2006;Zhu et al, 2010), and a direct interaction has been reported between TPL and Jumonji8, a histone demethylase (Macrae and Long, 2011). Furthermore, a direct link between JAZ1 and HDA6 (At5g63110) has recently been established, although the JAZ domain necessary for this interaction has not been mapped precisely (Zhu et al, 2011).…”

The wheat NB‐LRR gene TaRCR1 is required for host defence response to the necrotrophic fungal pathogen Rhizoctonia cerealis

“…In plants, activation of R proteins leads to extensive transcriptional reprogramming of defence genes (Chang et al ., 2013; Inoue et al ., 2013; Padmanabhan et al ., 2013; Shen et al ., 2007; Zhu et al ., 2010). Different regulatory proteins may activate different kinds of genes in wheat defence response to R. cerealis .…”

SUMO-, MAPK-, and resistance protein-signaling converge at transcription complexes that regulate plant innate immunity

“…A more direct link between an R protein and SUMOylation is exemplified by the Arabidopsis thaliana SNC1 protein. SNC1 was shown to interact directly with TPR1 and HDA19, 10 which indicates that SNC1 and possibly related R proteins (i.e., TIR-NB-LRR proteins) interact in the nucleus with SUMO-modified transcriptional co-repressors. These repressors might prevent activation of the plant defense response in non-infected plants.…”