Effect of rbf1 deletion during controlled expression of Ustilago maydis b-mating type locus genes bE1 and bW2

In the phytopathogenic Basidiomcete Ustilago maydis, sexual and pathogenic development are tightly connected and controlled via the b-mating type locus. The b-mating type locus encodes two homeodomain transcription factors, bE and bW, which form an active heterodimeric complex when they are derived from different b-alleles. Rbf1 encodes a zinc-finger transcription factor that is expressed upon formation of an active bE/bW heterodimer. To analyse the dependency of b and rbf1, changes in gene expression were monitored in strain AB31 (Brachmann et al., 2001, Mol Microbiol 42, 1047-1063) and in the derivative AB31Δrbf1 in which rbf1 was deleted. AB31 harbours the active combination bE1 and bW2 under the control of the arabinose-inducible crg1 promoter. Samples were taken 3h, 5h and 12h after induction of bE/bW gene expression. Strain AB32, which harbors the incompatible bE2 and bW2 combination, was used as control. Strains were grown to an OD600 of 0.4-0.6 at 28°C in liquid array medium: 6.25% (w/v) salt solution, 30 mM L-glutamine, 1% (w/v) glucose, pH 7.0 (filter-sterilized). For induction of the bE and bW genes, cells were inoculated in liquid array medium containing 1% (w/v) arabinose instead of glucose as a carbon source. For induction, cells were washed once with inducing medium; time point 0 h of the time course experiments corresponds to the first contact with inducing medium. Experiments were performed in two biological replicates for each time point.