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

¹State Key Laboratory of Plant Cell and Chromosome Engineering, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing 100101, China; ²Graduate University of Chinese Academy of Sciences, Beijing 100049, China; ³Graduate School Experimental Plant Sciences, Wageningen, The Netherlands; ⁴Plant Research International, P.O. Box 6708 PB, Wageningen, The Netherlands; ⁵Wageningen University, Laboratory of Phytopathology, P.O. Box 6708 PB, Wageningen, The Netherlands; ⁶Department of Botany and Microbiology, King Saud University, Ryadh, Saudi Arabia

Zn₂Cys₆ 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 Zn₂Cys₆ 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-1Δebr1 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-1Δebr1 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-1Δebr1 mutant, which may be due to the presence of multiple orthologous genes in this fungus. Transformation of FOXG_05408 into PH-1Δebr1 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.