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CPTF1, a CREB-Like Transcription Factor, Is Involved in the Oxidative Stress Response in the Phytopathogen Claviceps purpurea and Modulates ROS Level in Its Host Secale cereale

CPTF1, a transcription factor with significant homology to ATF/CREB bZIP factors, was identified during an expressed sequence tag (EST) analysis of in planta-expressed genes of the phytopathogen Claviceps purpurea. Using a gene-replacement approach, deletion mutants of cptf1 were created. Expression studies in axenic culture showed that the H₂O₂-inducible gene cpcat1 (encoding a secreted catalase) had a reduced basal expression level and no longer responded to oxidative stress in the Δcptf1 mutant. Biochemical analyses indicated that CPTF1 is a general regulator of catalase activity. Δcptf1 mutants showed significantly reduced virulence on rye. Electron microscopical in situ localization revealed significant amounts of H₂O₂ in Δcptf1-infected rye epidermal tissues, indicating that the plant tissue displayed an oxidative burst-like reaction, an event not detected in wild-type infections. These data indicate that CPTF1 is involved not only in oxidative stress response in the fungus but also in modulation of the plant's defense reactions.