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. Our results show that the Arabidopsis thaliana TX14 (AtTX14) gene encodes four distinct protein isoforms generated through alternative splicing. These isoforms differ in their overall domain composition and the integrity of the TIR domain. Among them, AtTX14 2IR, an isoform composed solely of an intact TIR domain, was both necessary and sufficient to induce the hypersensitive response (HR). Mechanistically, AtTX14 2IR localized to both the cytoplasm and the nucleus, whereas the two other functional isoforms, AtTX14 Full and Fusion, localized exclusively to the cytoplasm. Furthermore, simultaneous mutation of four clustered basic amino acids in AtTX14 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 Enhanced Disease Susceptibility 1-dependency in mediating the HR phenotype.