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Novel positive regulatory role for the SPL6 transcription factor in the N TIR-NB-LRR receptor-mediated plant innate immunity.

ABSTRACT: Following the recognition of pathogen-encoded effectors, plant TIR-NB-LRR immune receptors induce defense signaling by a largely unknown mechanism. We identify a novel and conserved role for the SQUAMOSA PROMOTER BINDING PROTEIN (SBP)-domain transcription factor SPL6 in enabling the activation of the defense transcriptome following its association with a nuclear-localized immune receptor. During an active immune response, the Nicotiana TIR-NB-LRR N immune receptor associates with NbSPL6 within distinct nuclear compartments. NbSPL6 is essential for the N-mediated resistance to Tobacco mosaic virus. Similarly, the presumed Arabidopsis ortholog AtSPL6 is required for the resistance mediated by the TIR-NB-LRR RPS4 against Pseudomonas syringae carrying the avrRps4 effector. Transcriptome analysis indicates that AtSPL6 positively regulates a subset of defense genes. A pathogen-activated nuclear-localized TIR-NB-LRR like N can therefore regulate defense genes through SPL6 in a mechanism analogous to the induction of MHC genes by mammalian immune receptors like CIITA and NLRC5.

SUBMITTER: Padmanabhan MS

PROVIDER: S-EPMC3597514 | biostudies-literature | 2013 Mar

REPOSITORIES: biostudies-literature

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Novel positive regulatory role for the SPL6 transcription factor in the N TIR-NB-LRR receptor-mediated plant innate immunity.

Padmanabhan Meenu S MS Ma Shisong S Burch-Smith Tessa M TM Czymmek Kirk K Huijser Peter P Dinesh-Kumar Savithramma P SP

PLoS pathogens 20130314 3

Following the recognition of pathogen-encoded effectors, plant TIR-NB-LRR immune receptors induce defense signaling by a largely unknown mechanism. We identify a novel and conserved role for the SQUAMOSA PROMOTER BINDING PROTEIN (SBP)-domain transcription factor SPL6 in enabling the activation of the defense transcriptome following its association with a nuclear-localized immune receptor. During an active immune response, the Nicotiana TIR-NB-LRR N immune receptor associates with NbSPL6 within d ...[more]

PMID: 23516366

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Project description:Plants react to pathogen attack via recognition of, and response to, pathogen-specific molecules at the cell surface and inside the cell. Pathogen effectors (virulence factors) are monitored by intracellular nucleotide-binding leucine-rich repeat (NB-LRR) sensor proteins in plants and mammals. Here, we study the genetic requirements for defense responses of an autoactive mutant of ADR1-L2, an Arabidopsis coiled-coil (CC)-NB-LRR protein. ADR1-L2 functions upstream of salicylic acid (SA) accumulation in several defense contexts, and it can act in this context as a "helper" to transduce specific microbial activation signals from "sensor" NB-LRRs. This helper activity does not require an intact P-loop. ADR1-L2 and another of two closely related members of this small NB-LRR family are also required for propagation of unregulated runaway cell death (rcd) in an lsd1 mutant. We demonstrate here that, in this particular context, ADR1-L2 function is P-loop dependent. We generated an autoactive missense mutation, ADR1-L2D484V, in a small homology motif termed MHD. Expression of ADR1-L2D848V leads to dwarfed plants that exhibit increased disease resistance and constitutively high SA levels. The morphological phenotype also requires an intact P-loop, suggesting that these ADR1-L2D484V phenotypes reflect canonical activation of this NB-LRR protein. We used ADR1-L2D484V to define genetic requirements for signaling. Signaling from ADR1-L2D484V does not require NADPH oxidase and is negatively regulated by EDS1 and AtMC1. Transcriptional regulation of ADR1-L2D484V is correlated with its phenotypic outputs; these outputs are both SA-dependent and -independent. The genetic requirements for ADR1-L2D484V activity resemble those that regulate an SA-gradient-dependent signal amplification of defense and cell death signaling initially observed in the absence of LSD1. Importantly, ADR1-L2D484V autoactivation signaling is controlled by both EDS1 and SA in separable, but linked pathways. These data allows us to propose a genetic model that provides insight into an SA-dependent feedback regulation loop, which, surprisingly, includes ADR1-L2.

Project description:The Toll/interleukin-1 receptor (TIR) domain is a protein-protein interaction domain that is found in both animal and plant immune receptors. The N-terminal TIR domain from the nucleotide-binding (NB)-leucine-rich repeat (LRR) class of plant disease-resistance (R) proteins has been shown to play an important role in defence signalling. Recently, the crystal structure of the TIR domain from flax R protein L6 was determined and this structure, combined with functional studies, demonstrated that TIR-domain homodimerization is a requirement for function of the R protein L6. To advance the molecular understanding of the function of TIR domains in R-protein signalling, the protein expression, purification, crystallization and X-ray diffraction analyses of the TIR domains of the Arabidopsis thaliana R proteins RPS4 (resistance to Pseudomonas syringae 4) and RRS1 (resistance to Ralstonia solanacearum 1) and the resistance-like protein SNC1 (suppressor of npr1-1, constitutive 1) are reported here. RPS4 and RRS1 function cooperatively as a dual resistance-protein system that prevents infection by three distinct pathogens. SNC1 is implicated in resistance pathways in Arabidopsis and is believed to be involved in transcriptional regulation through its interaction with the transcriptional corepressor TPR1 (Topless-related 1). The TIR domains of all three proteins have successfully been expressed and purified as soluble proteins in Escherichia coli. Plate-like crystals of the RPS4 TIR domain were obtained using PEG 3350 as a precipitant; they diffracted X-rays to 2.05 Å resolution, had the symmetry of space group P1 and analysis of the Matthews coefficient suggested that there were four molecules per asymmetric unit. Tetragonal crystals of the RRS1 TIR domain were obtained using ammonium sulfate as a precipitant; they diffracted X-rays to 1.75 Å resolution, had the symmetry of space group P4(1)2(1)2 or P4(3)2(1)2 and were most likely to contain one molecule per asymmetric unit. Crystals of the SNC1 TIR domain were obtained using PEG 3350 as a precipitant; they diffracted X-rays to 2.20 Å resolution and had the symmetry of space group P4(1)2(1)2 or P4(3)2(1)2, with two molecules predicted per asymmetric unit. These results provide a good foundation to advance the molecular and structural understanding of the function of the TIR domain in plant innate immunity.

Dataset Information

Novel positive regulatory role for the SPL6 transcription factor in the N TIR-NB-LRR receptor-mediated plant innate immunity.

Publications

Novel positive regulatory role for the SPL6 transcription factor in the N TIR-NB-LRR receptor-mediated plant innate immunity.

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