A novel Zn2 Cys6 transcription factor BcGaaR regulates D-galacturonic acid utilization in Botrytis cinerea

D-galacturonic acid (GalA) is the most abundant monosaccharide component of pectin. Previous transcriptome analysis in the plant pathogenic fungus Botrytis cinerea identified eight GalA-inducible genes involved in pectin decomposition, GalA transport and utilization. Co-expression of these genes indicates that a specific regulatory mechanism occurs in B. cinerea. In this study, promoter regions of these genes were analysed and eight conserved sequence motifs identified. The Bclga1 promoter, containing all these motifs, was functionally analysed and the motif designated GalA Responsive Element (GARE) was identified as the crucial cis-regulatory element in regulation of GalA utilization in B. cinerea. Yeast one-hybrid screening with the GARE motif led to identification of a novel Zn2 Cys6 transcription factor (TF), designated BcGaaR. Targeted knockout analysis revealed that BcGaaR is required for induction of GalA-inducible genes and growth of B. cinerea on GalA. A BcGaaR-GFP fusion protein was predominantly localized in nuclei in mycelium grown in GalA. Fluorescence in nuclei was much stronger in mycelium grown in GalA, as compared to fructose and glucose. This study provides the first report of a GalA-specific TF in filamentous fungi. Orthologs of BcGaaR are present in other ascomycete fungi that are able to utilize GalA, including Aspergillus spp., Trichoderma reesei and Neurospora crassa.