- The fungal pathogen Cochliobolus victoriae, the causal agent of Victoria blight, produces a host-selective pathogenicity factor called victorin. In Arabidopsis thaliana, a dominant gene called "supersense" (SSN) confers constitutive victorin sensitivity at very low concentrations. SSN encodes a nucleotide-binding leucine-rich-repeat (NB-LRR) protein. In the SSN-carrying Heiligkreuztal 2 ecotype (TAIR Germplasm Stock CS76404) of Arabidopsis thaliana, a mutagenic approach was undertaken to reveal the presence of second-site mutations conferring insensitivity to victorin. Genetic analysis identified several mutants possessing a functional SSN allele while displaying insensitivity to victorin. These data suggest that at least one additional gene is required for SSN gene function and expression of the victorin super-sensitive phenotype.
Previous studies in Avena sativa indicate that Victoria blight susceptibility, conferred by the Vb gene, and crown rust resistance, conferred by the Pc2 gene, are genetically inseparable, suggesting that these distinct responses may actually be controlled by the same gene. We undertook a mutagenic analysis of the victorin-sensitive Victoria cultivar to assess the correlation between these distinct disease phenotypes. In nearly all victorin-insensitive mutants identified, loss of sensitivity to victorin also resulted in the complete loss of resistance to rust. This finding supports the assertion that Vb and Pc2 are the same gene and Vb/Pc2 is responsible for both victorin sensitivity and rust resistance. These responses are likely mediated by an NB-LRR protein.