Ftf2 encodes a fungal transcription factor involved in growth but not in pathogenicity

The gene ftf2, encoding a transcription factor with a Zn(II)2-Cys6 binuclear cluster DNA- binding motif, was discovered in Fusarium oxysporum f.sp. phaseoli and homologs are found in other pathogenic and non-pathogenic fungi. Southern and genome analyses detected a single ftf2 copy. Previously, a multicopy gene (ftf1) was characterized that is highly homologous to ftf2. Ftf1 is only present in highly virulent strains of F. oxysporum and is dramatically upregulated during the early stages of the infection. To date, however, the function of the ftf2 gene product is still unknown. Silencing of ftf2 was induced in F. oxysporum. Agrobacterium tumefaciens- mediated transfer of a hairpin-expression vector carrying fragments of the ftf2 gene allowed efficient silencing of ftf2 expression. The silenced transformants showed a reduction in their growing capacities and, possibly, a reduction in sporulation. However, no effect on pathogenicity was observed. Also, Real-time PCR analysis indicated that the expression of ftf2 is similar in all the strains and rather constant in time, suggesting a constitutive gene expression pattern for ftf2. Also, no upregulation or downregulations was observed in planta, confirming the absence of an important role for ftf2 in the infection process. Finally, in order to shed some light on the kind of genes regulated by the ftf2 transcription factor, a SSH library was constructed. Two mRNA populations were used that were obtained from the weakly virulent wild type strain FOP-SP4 and a ftf2 silenced FOP-SP4 transformant. Preliminary analysis of the library indicates the presence of genes that are expressed in the tester strain yet absent from the driver RNA, and thus are putatively regulated by the ftf2 transcription factor.