Victorin Binding to Proteins in Susceptible and Resistant Oat Genotypes

Abstract

Cochliobolus victoriae Nelson (Helminthosporium victoriae Meehan et Murphy) produces the host-specific toxin, victorin. Cultivars of oats with the dominant Hv allele are susceptible to the fungus and sensitive to victorin, but victorin does not affect the recessive (resistant) genotypes. Recently, we have isolated and characterized victorin as a group of closely related peptides. Through chemical modification of victorin several derivatives were prepared. These derivatives include compounds which are less active than native toxin but still host-specific, non-toxic compounds, and a non-toxic protective compound, i. e., pre-i ncubati on with the protectant prevents the toxic effects of subsequent addition of native toxin. These chemical manipulations have provided the means to radioiodinate victorin to specific activities of >2000 Ci/mmole for use as a probe of victorin binding, and to produce other probes of varying biological activities. By treating near-isogenic lines of oats differing in the Hv gene, with radiolabelled victorin, we have identified a 100 kd protein which binds victorin covalently in a genotype-specific and a ligand-specific manner.