| Popis: |
Maize Helminthosporium leaf spot and ear mold is caused by Cochliobolus carbonum race l, a fungal pathogen for which infection is dependent upon production of the cyclic tetrapeptide HC-toxin (Walton, 1996; Walton et al., 1982). Compatible interaction and disease occur only in maize lines homozygous for a mutation in the Hml gene; the encoded wild-type enzyme is an NADPH-dependent reductase that converts HC-toxin to an inactive form (). The observation that the toxin is a specific inhibitor of maize histone deacetylases (Brosch et al., 1995; Ransom and Walton, 1997) has led to the hypothesis that the molecular basis for compatibility in this system is maintenance of a chromatin state in which induced expression of disease defense response genes is prevented without lethal repression of all transcription. Such an effect would explain the cytostasis often observed in cells exposed to pure HC-toxin and would produce metabolically active yet undefended host tissue for fungal infection. |
