EBR1, a Novel Zn2Cys6 Transcription Factor, Affects Virulence and Apical Dominance of the Hyphal Tip in Fusarium graminearum

Zn(2)Cys(6) transcription factors are unique to fungi and have been reported to be involved in different regulatory functions. Here, we characterized EBR1 (enhanced branching 1), a novel Zn(2)Cys(6) transcription factor of Fusarium graminearum. Knocking out EBR1 in F. graminearum PH-1 caused reduction of both radial growth and virulence. The conidia of knock-out strain PH-1 Delta ebr1 germinated faster than those of wild-type PH-1, but the conidiation of the mutant was significantly reduced. Detailed analysis showed that the reduced radial growth might be due to reduced apical dominance of the hyphal tip, leading to increased hyphal branching. Inoculation assays on wheat heads with a green fluorescent protein (GFP)-labeled PH-1 Delta ebr1 mutant showed that it was unable to penetrate the rachis of the spikelets. Protein fusion with GFP showed that EBR1 is localized in the nucleus of both conidia and hyphae. Knocking out the orthologous gene FOXG_05408 in F. oxysporum f. sp. lycopersici caused a much weaker phenotype than the PH-1 Delta ebr1 mutant, which may be due to the presence of multiple orthologous genes in this fungus. Transformation of FOXG_05408 into PH-1 Delta ebr1 restored the mutant phenotype. Similar to EBR1, FOXG_05408 is localized in the nucleus of F. oxysporum f. sp. lycopersici. Possible functions of EBR1 and its relation with other fungal transcription factors are discussed.