A Gain-of-Function Mutation in a Plant Disease Resistance Gene Leads to Constitutive Activation of Downstream Signal Transduction Pathways in suppressor of npr1-1, constitutive 1

Abstract

Plants have evolved sophisticated defense mechanisms against pathogen infections, during which resistance ( R ) genes play central roles in recognizing pathogens and initiating defense cascades. Most of the cloned R genes share two common domains: the central domain, which encodes a nucleotide binding adaptor shared by APAF-1, certain R proteins, and CED-4 (NB-ARC), plus a C-terminal region that encodes Leu-rich repeats (LRR). In Arabidopsis, a dominant mutant, suppressor of npr1-1 , constitutive 1 ( snc1 ), was identified previously that constitutively expresses pathogenesis-related ( PR ) genes and resistance against both Pseudomonas syringae pv maculicola ES4326 and Peronospora parasitica Noco2. The snc1 mutation was mapped to the RPP4 cluster. In snc1 , one of the TIR-NB-LRR-type R genes contains a point mutation that results in a single amino acid change from Glu to Lys in the region between NB-ARC and LRR. Deletions of this R gene in snc1 reverted the plants to wild-type morphology and completely abolished constitutive PR gene expression and disease resistance. The constitutive activation of the defense responses was not the result of the overexpression of the R gene, because its expression level was not altered in snc1 . Our data suggest that the point mutation in snc1 renders the R gene constitutively active without interaction with pathogens. To analyze signal transduction pathways downstream of snc1 , epistasis analyses between snc1 and pad4-1 or eds5-3 were performed. Although the resistance signaling in snc1 was fully dependent on PAD4 , it was only partially affected by blocking salicylic acid (SA) synthesis, suggesting that snc1 activates both SA-dependent and SA-independent resistance pathways.

Novel Plant Immune-Priming Compounds Identified via High-Throughput Chemical Screening Target Salicylic Acid Glucosyltransferases in Arabidopsis

“…For example, benzothiadiazole (commercial product Actigard) is a synthetic analog of SA (Görlach et al, 1996;Lawton et al, 1996). However, strong induction of a defense response is often accompanied by growth inhibition (Shirano et al, 2002;Zhang et al, 2003;Noutoshi et al, 2005), limiting the usefulness of these compounds in the field. Similarly, probenazole (Oryzemate) suppresses growth when sprayed on leaves, but not when taken up by the roots.…”

COS1: An Arabidopsis coronatine insensitive1 Suppressor Essential for Regulation of Jasmonate-Mediated Plant Defense and Senescence

“…In Arabidopsis, suppressor screens have been used to identify genes/mutants functional in many pathways, including the auxin (Cernac et al, 1997), gibberellin (Jacobsen and Olszewski, 1993;Wilson and Somerville, 1995), and abscisic acid (Koorneef et al, 1982) pathways as well as the systemic acquired resistance pathway (Li et al, 1999;Zhang et al, 2003).…”

Mitochondrial AtPAM16 is required for plant survival and the negative regulation of plant immunity

“…Leaf punches were taken at day 0 and day 3. Colony-forming units were determined after serial dilution and bacterial incubation at 28°C on LB plates 5 .…”

“…Arabidopsis SNC1 (SUPPRESSOR OF NPR1-1, CONSTITU-TIVE 1) encodes a TIR-type NB-LRR protein 4,5 . In the gain-offunction mutant allele snc1, a point mutation in the linker region between the NB and LRR results in a Glu-to-Lys change, which leads to the constitutive activation of defence responses without pathogen interaction.…”