A novel class of eukaryotic zinc-binding proteins is required for disease resistance signaling in barley and development in C-elegans

Barley Rar1 is a convergence point in the signaling of resistance to powder y mildew, triggered by multiple race-specific resistance (R) genes. Rar1 is shown to function upstream of H2O2 accumulation in attacked host cells, wh ich precedes localized host cell death. We isolated Rar1 by map-based cloni ng. The sequence of the deduced 25.5 kDa protein reveals two copies of a 60 -amino acid domain, CHORD, conserved in tandem organization in protozoa, pl ants, and metazoa. CHORD defines a novel eukaryotic Zn2+-binding domain. Si lencing of the C. elegans CHORD-containing gene, chp, results in semisteril ity and embryo lethality, suggesting an essential function of the wild-type gene in nematode development. Our findings indicate that plant R genes hav e recruited a fundamental cellular control element for signaling of disease resistance and cell death.