Submitted to: Molecular Plant-Microbe Interactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/13/2006
Publication Date: 11/1/2006
Citation: Jafary, H., Szabo, L.J., Niks, R.E. 2006. Innate Non-Host Immunity in Barley to Different Heterologous Rust Fungi is Controlled by Sets of Resistance Genes with Different and Overlapping Specificities. Molecular Plant-Microbe Interactions. 11:1270-1279. Interpretive Summary: Plants have two different basic mechanisms for protection against pathogens, a general non-specific system (innate resistance) and a specific system (race-specific). Race-specific system is fairly well described genetically and is governed by single dominant genes. However, innate resistance is more complex and resistance involves many genes. As a result, little is known genetically about innate resistance. In this study, 18 chromosome regions involved in innate resistance to rust fungi were mapped in barley. Seven rust species were used in this study and for each rust, a different set of genes are involved. In addition, most of the identified regions (11 out of 18) were involved in resistance to only one rust species. However, 7 of the regions had effect on resistance to more than one rust species. This work provides scientists with a relevant model system (barley-rust fungi) to study the inheritance and specificity of plant factors that determine the innate resistance.
Technical Abstract: We developed an evolutionary relevant model system, barley-Puccini rust fungi, to study the inheritance and specificity of plant factors that determine to what extent innate nonhost immunity can be suppressed. A mapping population was developed from a cross between an experimental barley line (Suspired) with exceptional susceptibility to several heterogonous (nonhost) rust fungi and regular, immune, cv. Veda. Seedlings were inoculated with five heterogonous and two homologous (host) species of rust fungi. Resistance segregated quantitatively for each of the rust fungi. In total, 18 chromosome regions were implicated. For each rust species, a different set of genes was effective. Of the 18 chromosomal regions, 11 were significantly effective to only one rust species and 7 were effective to more than one rust species, implying genetic linkage or pleiotrophy. One resistance (R) gene for hypersensitive resistance to Puccinia hordei-secalini was mapped, suggesting occasional contribution of R genes to nonhost resistance in barley. Quantitative trait loci (QLTs) with effects to multiple rust fungi did not tend to be particularly effective to rust species that were phylogenetically related, as determine from their internal transcribed spacer sequence. We suggest that the QLTs described here play a role as specific and quantitative recognition factors that are specifically negated by the rust to successfully suppress innate immunity.