RESEARCH ARTICLE Characterization of Cercospora nicotianae Hypothetical Proteins in Cercosporin Resistance

The photoactivated toxin, cercosporin, produced by Cercospora species, plays an impor-tant role in pathogenesis of this fungus to host plants. Cercosporin has almost universal tox-icity to cells due to its production of reactive oxygen species including singlet oxygen. For that reason,Cercospora species, which are highly resistant to their own toxin, are good can-didates to identify genes for resistance to cercosporin and to the reactive oxygen species it produces. In previous research, the zinc cluster transcription factor CRG1 (cercosporin resistance gene 1) was found to be crucial for Cercospora species ’ resistance against cer-cosporin, and subtractive hybridization analysis identified 185 genes differentially expressed between Cercospora nicotianae wild type (wt) and a crg1mutant. The focus of this work was to identify and characterize the hypothetical proteins that were identified in the Cercospora nicotianae subtractive library as potential resistance factors. Quantitative RT-PCR analysis of the 20 genes encoding hypothetical proteins showed that two, 24cF and 71cR, were induced under conditions of cercosporin toxicity, suggesting a role in resis-tance. Transformation and expression of 24cF and 71cR in the cercosporin-sensitive fun