title: The Arabidopsis resistance-like gene SNC1 is activated by mutations in SRFR1 and contributes to resistance to the bacterial effector AvrRps4.
abstract: The SUPPRESSOR OF rps4-RLD1 (SRFR1) gene was identified based on enhanced AvrRps4-triggered resistance in the naturally susceptible Arabidopsis accession RLD. No other phenotypic effects were recorded, and the extent of SRFR1 involvement in regulating effector-triggered immunity was unknown. Here we show that mutations in SRFR1 in the accession Columbia-0 (Col-0) lead to severe stunting and constitutive expression of the defense gene PR1. These phenotypes were temperature-dependent. A cross between srfr1-1 (RLD background) and srfr1-4 (Col-0) showed that stunting was caused by a recessive locus in Col-0. Mapping and targeted crosses identified the Col-0-specific resistance gene SNC1 as the locus that causes stunting. SRFR1 was proposed to function as a transcriptional repressor, and SNC1 is indeed overexpressed in srfr1-4. Interestingly, co-regulated genes in the SNC1 cluster are also upregulated in the srfr1-4 snc1-11 double mutant, indicating that the overexpression of SNC1 is not a secondary effect of constitutive defense activation. In addition, a Col-0 RPS4 mutant showed full susceptibility to bacteria expressing avrRps4 at 24°C but not at 22°C, while RLD susceptibility was not temperature-dependent. The rps4-2 snc1-11 double mutant showed increased, but not full, susceptibility at 22°C, indicating that additional cross-talk between resistance pathways may exist. Intriguingly, when transiently expressed in Nicotiana benthamiana, SRFR1, RPS4 and SNC1 are in a common protein complex in a cytoplasmic microsomal compartment. Our results highlight SRFR1 as a convergence point in at least a subset of TIR-NBS-LRR protein-mediated immunity in Arabidopsis. Based on the cross-talk evident from our results, they also suggest that reports of constitutive resistance phenotypes in Col-0 need to consider the possible involvement of SNC1.
authors.affiliation: Division of Plant Sciences, Christopher S. Bond Life Sciences Center and Interdisciplinary Plant Group, University of Missouri, Columbia, Missouri, United States of America.
authors.forename: Sang Hee
authors.initials: SH
authors.lastname: Kim
authors.forename: Fei
authors.initials: F
authors.lastname: Gao
authors.forename: Saikat
authors.initials: S
authors.lastname: Bhattacharjee
authors.forename: Joseph A
authors.initials: JA
authors.lastname: Adiasor
authors.forename: Ji Chul
authors.initials: JC
authors.lastname: Nam
authors.forename: Walter
authors.initials: W
authors.lastname: Gassmann
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics* / Q000382:microbiology*; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D003001:Cloning, Molecular; D018506:Gene Expression Regulation, Plant; D007113:Immunity, Innate; D015151:Immunoblotting; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics*; D010641:Phenotype; D010935:Plant Diseases / Q000235:genetics / Q000276:immunology / Q000382:microbiology*; D018515:Plant Leaves / Q000166:cytology / Q000378:metabolism / Q000382:microbiology; D030821:Plants, Genetically Modified; D017386:Sequence Homology, Amino Acid; D014026:Nicotiana / Q000382:microbiology
chemical_list: D029681:Arabidopsis Proteins; C098294:AvrRps4 protein, Pseudomonas syringae; D001426:Bacterial Proteins; C482739:SNC1 protein, Arabidopsis; C543708:SRFR1 protein, Arabidopsis