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 characteristics 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.