CULTIVAR-SPECIFIC ELICITATION OF BARLEY DEFENSE REACTIONS BY THE PHYTOTOXIC PEPTIDE NIP1 FROM RHYNCHOSPORIUM-SECALIS

Resistance of barley to the phytopathogenic fungus, Rhynhosporium secalis race US238.1, was found to be controlled by resistance gene Rrs1, which segregated in a manner characteristic for a codominant gene. PRHV-1, a thaumatin-like pathogenesis-related protein, was shown to be encoded by a gene family on chromosome 1. As part of the barley defense response, significant accumulation of PRHV-1 and peroxidase transcripts was induced early during pathogenesis in two Rrs1 cultivars but not or to a lower level in a near-isogenic, susceptible rrs1 cultivar or a cultivar lacking known resistance genes. R. secalis secretes a small group of necrosis-inducing peptides. One of these, NIP1, which was detected in culture filtrates only of fungal race US238.1, was found to elicit the accumulation of PRHv-1 and peroxidase mRNAs in Rrs1 cultivars with a time course similar to that upon fungal infection. Therefore, NIP1 is a candidate for the product of fungal avirulence gene avrRrs1, which, together with barley resistance gene Rrs1, determines incompatibility of the interaction.