Domain compositions of Arabidopsis Toll/Interleukin-1 Receptor/Resistance domain-containing TX14 proteins affect localization and induction of the hypersensitive response.

Plant Toll/Interleukin-1 Receptor/Resistance (TIR) domains produce small signaling molecules that activate immune responses. In this study we show that the Arabidopsis TX14 gene encodes four distinct protein isoforms that are generated through alternative splicing. These isoforms differ in their overall domain composition and the integrity of the TIR domain. Among them, TX14 2IR, an isoform composed solely of an intact TIR domain, was found to be both necessary and sufficient to induce the hypersensitive response (HR). Mechanistically, TX14 2IR localizes to both the cytoplasm and the nucleus, whereas the two other functional isoforms, TX14 Full and Fusion, localize exclusively to the cytoplasm. Furthermore, simultaneous mutation of four clustered basic amino acids in TX14 2IR abolished its deoxyribonuclease activity and delayed HR induction. Collectively, our findings demonstrate that the domain architecture of TIR domain-containing proteins influences their subcellular localization and their dependency on ENHANCED DISEASE SUSCEPTIBILITY 1 in mediating the HR phenotype.