P-390 - Transcription factors affecting gene expression in Blumeria hordei haustoria and barley powdery mildew virulence

Powdery mildew diseases caused by obligate biotrophic fungi are affecting many crops, including B. hordei (Bh) infecting barley. PM biotrophic lifestyle depend on haustorial structures to absorb nutrients from- and deliver effectors to invaded host epidermal cells. However, transcription factors (TFs) responsible for upregulated gene expression in PM haustoria are yet to be identified. Therefore, motifs enriched in promoters of haustoria expressed genes were investigated, identifying pH regulatory elements (PRE) recognised by pH alkaline response PacC/RIM101, zinc regulatory elements (ZRE) recognised by ZAP1, redox responses elements recognised by yeast bZIP YAP1p, elements recognised by Zn(2)-C6 fungal TFs such as GAL4 and xylanolytic activator (xlnR). BhPap1 (YAP1p), BhZnk (Zn-knuckle) and BhTF4072 (XlnR) were upregulated in haustoria. Moreover, a transient gene silencing assay evidenced that these TFs and BhPacC are required for B. hordei virulence, while affecting gene expression of RNAse-like BEC1011 (CSEP0264) and BEC1019 metalloprotease-like effectors.  BEC1019 is homologous to Candida albicans PRA1 virulence factor regulated by PacC. We could also evidence the physical binding of BhPacC to PRE containing BEC1011 and BEC1019 promoters. Together, these data suggest that all four TFs investigated are key to B. hordei virulence by controlling effector gene expression in haustoria during PM infection in barley and some of these mechanisms might be conserved across PMs.