MAIZE 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 tor;in and Virulen ce factor produced by the fungal pathogen Cochliobolus carbonum, alkyl ated a number of bionucleophiles, including guanosine, guanosine-5'-mo nophosphate, poly d(GC) and DNA from maize genotypes that are suscepti ble or resistant to the pathogen. The toxin selectively altered in viv o protein synthesis in susceptible genotypes. Treatment of root tips o f the susceptible genotype with HC-toxin enhanced or induced the synth esis of some proteins and suppressed the synthesis of others, but inco rporation of H-3-leucine into protein was not affected. A biologically inactive form of the toxin, produced by hydrolysis of the epoxide gro up that is essential for activity, had no effect on the pattern of pro tein synthesis or on H-3-leucine incorporation. The toxin had no effec t on synthesis of specific proteins or on the incorporation of H-3-leu cine 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.