Abstract
Plant innate immunity depends on the function of a large number of intracellular immune receptor proteins, the majority of which are structurally similar to mammalian nucleotide-binding oligomerization domain (NOD)-like receptor (NLR) proteins. CHILLING SENSITIVE 3 (CHS3) encodes an atypical Toll/Interleukin 1 Receptor (TIR)-type NLR protein with an additional Lin-11, Isl-1 and Mec-3 (LIM) domain at its C-terminus. The gain-of-function mutant allele chs3-2D exhibits severe dwarfism and constitutively activated defense responses, including enhanced resistance to virulent pathogens, high defence marker gene expression, and salicylic acid accumulation. To search for novel regulators involved in CHS3-mediated immune signaling, we conducted suppressor screens in the chs3-2D and chs3-2D pad4-1 genetic backgrounds. Alleles of sag101 and eds1-90 were isolated as complete suppressors of chs3-2D, and alleles of sgt1b were isolated as partial suppressors of chs3-2D pad4-1. These mutants suggest that SAG101, EDS1-90, and SGT1b are all positive regulators of CHS3-mediated defense signaling. Additionally, the TIR-type NLR-encoding CSA1 locus located genomically adjacent to CHS3 was found to be fully required for chs3-2D-mediated autoimmunity. CSA1 is located 3.9 kb upstream of CHS3 and is transcribed in the opposite direction. Altogether, these data illustrate the distinct genetic requirements for CHS3-mediated defense signaling.
Highlights
Plant innate immunity depends on the function of a large number of intracellular immune receptor proteins, the majority of which are structurally similar to mammalian nucleotide-binding oligomerization domain (NOD)-like receptor (NLR) proteins
These mutants suggest that SENESCENCE-ASSOCIATED GENE101 (SAG101), ENHANCED DISEASE SUSCEPTIBILITY 1 (EDS1)-90, and SGT1b are all positive regulators of CHILLING SENSITIVE 3 (CHS3)-mediated defense signaling
In the chs32D mutant, a C1340 to Y1340 substitution close to the LIM domain of CHS3 leads to autoimmune phenotypes including increased PATHOGENESIS-RELATED (PR) gene expression, salicylic acid accumulation, and enhanced resistance to the virulent oomycete strain Hyaloperonospora arabidopsidis (H.a.) Noco[212]
Summary
Plant innate immunity depends on the function of a large number of intracellular immune receptor proteins, the majority of which are structurally similar to mammalian nucleotide-binding oligomerization domain (NOD)-like receptor (NLR) proteins. CHILLING SENSITIVE 3 (CHS3) encodes an atypical Toll/ Interleukin 1 Receptor (TIR)-type NLR protein with an additional Lin-11, Isl-1 and Mec-3 (LIM) domain at its C-terminus. The gain-of-function mutant allele chs3-2D exhibits severe dwarfism and constitutively activated defense responses, including enhanced resistance to virulent pathogens, high defence marker gene expression, and salicylic acid accumulation. In the chs32D mutant, a C1340 to Y1340 substitution close to the LIM domain of CHS3 leads to autoimmune phenotypes including increased PATHOGENESIS-RELATED (PR) gene expression, salicylic acid accumulation, and enhanced resistance to the virulent oomycete strain Hyaloperonospora arabidopsidis (H.a.) Noco[212]. Using map-based cloning and Sanger sequencing techniques we were able to clone a number of genes, including novel alleles of known downstream regulators of TNL-mediated signaling, such as SAG101, EDS1, and SUPPESSOR OF THE G2 ALLELE OF SKP1, b (SGT1b)[13]. Our study revealed that the autoimmunity of chs3-2D requires the genomically adjacent TNL gene CONSTITUTIVE SHADE-AVOIDANCE 1 (CSA1), as four independent mutant alleles of csa[1] were found to suppress the autoimmunity of chs3-2D
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