The WOPR protein Ros1 is a master regulator of sporogenesis and effector gene expression in the maize pathogen Ustilago maydis [RNA-Seq]. Mycosarcoma maydis

Goals: characterization of the transcription factor Ros1 in Ustilago maydis Methods: generation of deletion mutants, microscopic observations, ectopic expression of ros1, identification of Ros1 regulated genes by RNAseq and ChIP sequencing Results: Ros1 is not involved in plant colonization but is essential to trigger sporogenesis during late stages of infection. Premature expression of ros1 revealed that Ros1 counteracts the b-dependent filamentation program and induces morphological alterations resembling the early steps of sporogenesis. Transcriptional profiling and ChIP seq analyses revealed that Ros1 affects the expression of about 30 % of all U. maydis genes with 40% being direct targets. Cell wall remodeling and plasma membrane modifications are among the processes affected by Ros1 dependent regulation. Interestingly a large number of b-dependent genes including transcription factors and effector genes involved in biotrophy establishment were downregulated by Ros1 while a subset of novel “late effectors” were upregulated. Taken together our results indicate that Ros1 is a master regulator of sporogenesis in U. maydis and that the switch to sporogenesis is accompanied by the differential regulation of 75% of the effector genes. Overall design: Two samples corresponding to plant material infected with either U. maydis wild type strains FB1 x FB2 or the ros1 deletion strains FB1Dros1 x FB2Dros1 were analyzed in triplicate.