The Role of the Fusarium oxysporum FTF2 Transcription Factor in Host Colonization and Virulence

The FTF (Fusarium Transcription Factor) gene family is composed of two members (FTF1 and FTF2) with high sequence homology. Both genes encode Zn(II)2Cys6 binuclear zinc finger transcription factors involved in the modulation of virulence in the F. oxysporum species complex (FOSC). While FTF1 is a multicopy gene exclusive of highly virulent strains of FOSC and is located in the accessory genome, FTF2 is a single copy gene, located in the core genome, and well conserved in all filamentous ascomycete fungi, except yeast. The involvement of FTF1 in the colonization of the vascular system and regulation of the expression of SIX effectors has been stablished. To address the role of FTF2 we generated and characterized null FTF2 mutants in a F. oxysporum f. sp. phaseoli weakly virulent strain and analyzed them together with the equivalent mutants formerly obtained in a highly virulent strain. The results obtained highlight a role for FTF2 as a negative regulator of the production of macroconidia and demonstrate that it is required for full virulence and positive regulation of SIX effectors. In addition, gene expression analyses provide compelling evidence that FTF2 is involved in the regulation of hydrophobins likely required for plant colonization.