Expression data of FB2 vs. FB2khd4Delta

RNA-binding proteins constitute key factors of the posttranscriptional machinery. These regulatory proteins recognise specific elements within target transcripts to promote e.g. maturation, translation or stability of mRNAs. In Ustilago maydis, evidence is accumulating that posttranscriptional processes are important to determine pathogenicity. Deletion of khd4, encoding a predicted RNA-binding protein with five K homology (KH) domains, causes aberrant cell morphology and reduced virulence. Here, we demonstrate that Khd4 recognises the sequence AUACCC in vivo via its tandem KH domains 3 and 4. This sequence functions most likely as regulatory RNA element in U. maydis, since it accumulates in 3’ untranslated regions. Consistently, an independent transcriptional profiling approach revealed that the binding motif is significantly enriched in transcripts differentially regulated in khd4 strains. Since the vast majority of potential Khd4 target mRNAs exhibit increased expression in deletion mutants, Khd4 might promote mRNA instability. Mutants that fail to bind AUACCC resemble deletion mutants exhibiting altered cell morphology, disturbed filamentous growth and severely reduced virulence. Hence, RNA binding is essential for function of Khd4 stressing the importance of posttranscriptional control in regulating morphology and pathogenicity. keywords: gene deletion, RNA-binding protein, KH domain Strains FB2 (2 replicates, control) and FB2khd4Delta (2 individuals) were grown in minimal medium containing glucose and glutamine.