The Role of the Fusarium oxysporum FTF2 Transcription Factor in Host Colonization and Virulence in Common Bean Plants (Phaseolus vulgaris L.)

The FTF (Fusarium Transcription Factor) gene family is composed of two members (FTF1 and FTF2) with high-sequence homology that encode 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 mutants defective in FTF2 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 the positive regulation of SIX effectors. In addition, gene expression analyses provided compelling evidence that FTF2 is involved in the regulation of hydrophobins likely required for plant colonization.