An inhibitor-resistant histone deacetylase in the plant pathogenic fungus Cochliobolus carbonum

We have partially purified and characterized histone deacetylases of the pl ant pathogenic fungus Cochliobolus carbonum. Depending on growth conditions , this fungus produces HC-toxin, a specific histone deacetylase inhibitor. Purified enzymes were analyzed by immunoblotting, by immunoprecipitation, a nd for toxin sensitivity. The results demonstrate the existence of at least two distinct histone deacetylase activities. A high molecular weight compl ex (430 000) is sensitive to HC-toxin and trichostatin A and shows immunore activity with an antibody against Cochliobolus HDC2, an enzyme homologous t o yeast RPD3. The second activity, a 60 000 molecular weight protein, which is resistant even to high concentrations of well-known deacetylase inhibit ors, such as HC-toxin and trichostatin A, is not recognized by antibodies a gainst Cochliobolus HDC1 (homologous to yeast HOS2) or HDC2 and represents a different and/or modified histone deacetylase which is enzymatically acti ve in its monomeric form. This enzyme activity is not present in the relate d filamentous fungus Aspergillus nidulans. Furthermore, in vivo treatment o f Cochliobolus mycelia with trichostatin A and analysis of HDACs during the transition from non-toxin-producing to toxin-producing stages support an H C-toxin-dependent enzyme activity profile.