Maise DNA alkylation and genotype-specific alterations in protein synthesis induced by the host-selective toxin produced by cochliobolus carbonum

The cyclic tetrapeptide, HC-toxin, a host-selective toxin and virulence factor produced by the fungal pathogen Cochliobolus carbonum, alkylated a number of bionucleophiles, including guanosine, guanosine-5'-monophosphate, poly d(GC) and DNA from maize genotypes that are susceptible or resistant to the pathogen. The toxin selectively altered in vivo protein synthesis in susceptible genotypes. Treatment of root ups of the susceptible genotype with HC-toxin enhanced or induced the synthesis of some proteins and suppressed the synthesis of others, but incorporation of 3Hleucine into protein was not affected. A biologically inactive form of the toxin, produced by hydrolysis of the epoxide group that is essential for activity, had no effect on the pattern of protein synthesis or on 3H-leucine incorporation. The toxin had no effect on synthesis of specific proteins or on the incorporation of 3H-leucine in the near-isogenic resistant line. The results suggest that the toxic effects of HC-toxin are mediated through a modification of DNA and regulation of gene expression.