Gene expression in aerial hyphae in response to rep1 deletion in Ustilago maydis

The rep1 gene of the maize pathogen Ustilago maydis encodes a pre-pro-protein that is processed in the secretory pathway into 11 peptides. These so-called repellents form amphipathic amyloid fibrils at the surface of aerial hyphae. Strains in which the rep1 gene is inactivated (∆rep1 strain) are affected in aerial hyphae formation. This makes these strains instrumental to assess changes in global gene expression as a consequence of aerial growth. Microarray analysis revealed that only 31 genes in the ∆rep1 SG200 strain had a fold change in expression of >= 2. Twenty-two of these genes are up-regulated and half of them encode small secreted proteins (SSP’s) with unknown functions. Seven of the SSP genes and two other genes that are over-expressed in the ∆rep1 SG200 strain encode secreted cysteine-rich proteins (SCRP’s). Interestingly, most of the SCRP’s are predicted to form amyloids. The SCRP gene um00792 showed the highest up-regulation in the ∆rep1 strain. Using GFP as a reporter, it was shown that this gene is over-expressed in the layer of hyphae at the medium-air interface. Taken together, it is concluded that only minor changes occur in the expression profile when U. maydis forms aerial structures. Key words: aerial hypha, repellent, hydrophobin-like protein, Ustilago maydis, SSP, SCRP, fungal pathogenicity. To analyze expression changes in aerial hyphae upon deletion of the rep1 gene, strains SG200 and SG200∆rep1 were grown on charcoal nitrate minimal array media supplemented with vitamins and 1% glucose at 22 C for 48 h. For each experiment three biological replicates were performed.