Two homologous Zn2Cys6 transcription factors play crucial roles in host specificity of Colletotrichum orbiculare by controlling the expression of cucurbit-specific virulence effectors

We identified a Zn 2 Cys 6 transcription factor gene, named TFV1 (Transcription Factor for Virulence 1), which is required for full virulence of Colletotrichum orbiculare on its cucurbitaceous host plants.The additional deletion of a TFV1 paralog named TVL1 (TFV1-like 1) further decreased virulence on the cucurbit hosts.Expression of putative effector genes, including EPC1 to EPC4 that are specifically required for virulence on cucurbits, was commonly down-regulated in the tfv1 mutant and the tfv1 tvl1 mutant, indicating the importance of TFV1 for the expression of key effector genes.Yeast one-hybrid assays suggested that TFV1 binds to the putative promoter regions of EPC2, EPC3 and EPC4.Furthermore, among the putative effector genes whose expression was affected by TVL1 deletion, we identified a novel LysM effector gene that is specifically required for virulence on cucurbits.Nine candidate genes encoding putative transcriptional factors were selected based on RNA sequencing data of C. orbiculare for multiple conditions.Candidate genes were selected based on mean RPKM values in vegetative hypha (VH), conidia (Con), inoculated cucumber cotyledons at 24 hpi (Cs24h) and inoculated N. benthamiana leaves at 24 hpi (Nb24h).