title: The nuclear immune receptor RPS4 is required for RRS1SLH1-dependent constitutive defense activation in Arabidopsis thaliana.
abstract: Plant nucleotide-binding leucine-rich repeat (NB-LRR) disease resistance (R) proteins recognize specific "avirulent" pathogen effectors and activate immune responses. NB-LRR proteins structurally and functionally resemble mammalian Nod-like receptors (NLRs). How NB-LRR and NLR proteins activate defense is poorly understood. The divergently transcribed Arabidopsis R genes, RPS4 (resistance to Pseudomonas syringae 4) and RRS1 (resistance to Ralstonia solanacearum 1), function together to confer recognition of Pseudomonas AvrRps4 and Ralstonia PopP2. RRS1 is the only known recessive NB-LRR R gene and encodes a WRKY DNA binding domain, prompting suggestions that it acts downstream of RPS4 for transcriptional activation of defense genes. We define here the early RRS1-dependent transcriptional changes upon delivery of PopP2 via Pseudomonas type III secretion. The Arabidopsis slh1 (sensitive to low humidity 1) mutant encodes an RRS1 allele (RRS1SLH1) with a single amino acid (leucine) insertion in the WRKY DNA-binding domain. Its poor growth due to constitutive defense activation is rescued at higher temperature. Transcription profiling data indicate that RRS1SLH1-mediated defense activation overlaps substantially with AvrRps4- and PopP2-regulated responses. To better understand the genetic basis of RPS4/RRS1-dependent immunity, we performed a genetic screen to identify suppressor of slh1 immunity (sushi) mutants. We show that many sushi mutants carry mutations in RPS4, suggesting that RPS4 acts downstream or in a complex with RRS1. Interestingly, several mutations were identified in a domain C-terminal to the RPS4 LRR domain. Using an Agrobacterium-mediated transient assay system, we demonstrate that the P-loop motif of RPS4 but not of RRS1SLH1 is required for RRS1SLH1 function. We also recapitulate the dominant suppression of RRS1SLH1 defense activation by wild type RRS1 and show this suppression requires an intact RRS1 P-loop. These analyses of RRS1SLH1 shed new light on mechanisms by which NB-LRR protein pairs activate defense signaling, or are held inactive in the absence of a pathogen effector.
authors.affiliation: The Sainsbury Laboratory, Norwich Research Park, Norwich, United Kingdom; Bioprotection Research Centre, Institute of Agriculture and Environment, Massey University, Palmerston North, New Zealand.
authors.forename: Kee Hoon
authors.initials: KH
authors.lastname: Sohn
authors.affiliation: The Sainsbury Laboratory, Norwich Research Park, Norwich, United Kingdom; Bioprotection Research Centre, Institute of Agriculture and Environment, Massey University, Palmerston North, New Zealand.
authors.forename: Cécile
authors.initials: C
authors.lastname: Segonzac
authors.affiliation: The Sainsbury Laboratory, Norwich Research Park, Norwich, United Kingdom.
authors.forename: Ghanasyam
authors.initials: G
authors.lastname: Rallapalli
authors.affiliation: The Sainsbury Laboratory, Norwich Research Park, Norwich, United Kingdom.
authors.forename: Panagiotis F
authors.initials: PF
authors.lastname: Sarris
authors.affiliation: School of Life Sciences and Biotechnology, Korea University, Seoul, Republic of Korea.
authors.forename: Joo Yong
authors.initials: JY
authors.lastname: Woo
authors.affiliation: School of Chemistry and Molecular Biosciences, Institute for Molecular Bioscience and Australian Infectious Diseases Research Centre, University of Queensland, Brisbane, Australia.
authors.forename: Simon J
authors.initials: SJ
authors.lastname: Williams
authors.affiliation: Bioprotection Research Centre, Institute of Agriculture and Environment, Massey University, Palmerston North, New Zealand.
authors.forename: Toby E
authors.initials: TE
authors.lastname: Newman
authors.affiliation: School of Life Sciences and Biotechnology, Korea University, Seoul, Republic of Korea.
authors.forename: Kyung Hee
authors.initials: KH
authors.lastname: Paek
authors.affiliation: School of Chemistry and Molecular Biosciences, Institute for Molecular Bioscience and Australian Infectious Diseases Research Centre, University of Queensland, Brisbane, Australia.
authors.forename: Bostjan
authors.initials: B
authors.lastname: Kobe
authors.affiliation: The Sainsbury Laboratory, Norwich Research Park, Norwich, United Kingdom.
authors.forename: Jonathan D G
authors.initials: JD
authors.lastname: Jones
mesh_terms: D020816:Amino Acid Motifs; D017360:Arabidopsis / Q000235:genetics; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D002467:Cell Nucleus; D060467:Disease Resistance / Q000235:genetics*; D018506:Gene Expression Regulation, Plant; D009154:Mutation; D010935:Plant Diseases / Q000235:genetics* / Q000276:immunology; D057865:Plant Immunity / Q000235:genetics; D010940:Plant Proteins / Q000235:genetics*; D044224:Pseudomonas syringae / Q000472:pathogenicity; D043368:Ralstonia solanacearum / Q000472:pathogenicity
chemical_list: D029681:Arabidopsis Proteins; D010940:Plant Proteins; C582898:RRS1 protein, Arabidopsis; C097421:rps4 protein, plant