Structural and functional investigation of plant TIR domain interaction
X. ZHANG (1), M. Bernoux (1), S. Williams (2), K. Sohn (3), T. Newman (4), T. Ve (2), P. Dodds (1), B. Kobe (2) (1) Commonwealth Scientific and Industrial Research Organisation Agriculture, Australia; (2) School of Chemistry and Molecular Biosciences and Australian Infectious Diseases Research Centre, University of Queensland, Australia; (3) Dept. of Life Sciences, School of Interdisciplinary Bioscience and Bioengineering, Pohang University of Science and Technology, Korea; (4) Bio-protection Research Centre, Institute of Agriculture and Environment, Massey University, New Zealand; (5) School of Chemistry and Molecular Biosciences and Australian Infectious Diseases Research Centre, University of Queensland, Australia

The Toll/interleukin-1 receptor (TIR) domain is widespread in animal and plant immune receptors. In plants, most immune receptors belong to the nucleotide-binding domain and leucine-rich repeat (NB-LRR) family. A major sub-family of NB-LRR proteins, such as flax L6 and Arabidopsis RPS4, contain a TIR domain at their N-terminus. Previous investigation of L6 and RPS4 TIR domains showed that isolated TIR domains can trigger pathogen effector-independent cell death and that TIR domain self-association is required for this signalling activity. L6TIR self-associates through an interface involving residues from the αD and αE helices (L6-interface), while RPS4TIR self-associates through a different interface formed by the αA and αE helices (RPS4-interface). Here we report the crystal structure of the TIR domain from the Arabidopsis TIR-NB-LRR protein SNC1. Analysis of the structure combined with site-directed mutagenesis reveal two distinct dimerization interfaces that resemble the RPS4- and L6- interface, respectively. Mutations in the RPS4-interface abolish SNC1TIR self-association in solution. In addition, mutations in either RPS4- or L6- interface abolish SNC1TIR cell death signalling activity in planta. Although the RPS4-interface was not identified in the L6TIR crystal structure and vice versa, mutations in the RPS4-interface equivalent regions of L6 disrupt L6TIR self-association in yeast and depress L6TIR signalling in planta. For RPS4, mutations in predicted L6-interface abolish RPS4TIR self-association in yeast and affect RPS4TIR signalling. These data suggest that both interfaces are involved in plant TIR domain self-interaction and play distinct roles in TIR domain signalling function.

Abstract Number: P17-646
Session Type: Poster