The transcriptional activator Pti4 is required for the recruitment of a repressosome nucleated by repressor SEBF at the potato PR-10a gene.

Transcriptional reprogramming is critical for plant disease resistance responses. In potato (Solanum tuberosum), the marker gene PATHOGENESIS-RELATED-10a (PR-10a) is transcriptionally activated by pathogens, wounding, or elicitor treatment. Activation of PR-10a requires the recruitment of the activator Why1 to its promoter. In addition, PR-10a is negatively regulated by the repressor SEBF (for Silencer Element Binding Factor). Here, we show through a yeast two-hybrid screen that SEBF interacts with Pti4, which has been shown to be a transcriptional activator. SEBF recruits Pti4 via its consensus sequence-type RNA binding domain, while Pti4 is recruited to SEBF by means of its ethylene-response factor domain. In vivo plant transcription assays confirmed that SEBF interacts with Pti4 to form a repressosome, showing that Pti4 can also play a role in transcriptional repression. Chromatin immunoprecipitation revealed that both SEBF and Pti4 are recruited to the PR-10a promoter in uninduced conditions only and that the recruitment of Pti4 is dependent on the presence of SEBF, consistent with the fact that there is no Pti4 consensus binding site in PR-10a. Unexpectedly, we also demonstrated that recruitment of SEBF was dependent on the presence of Pti4, thereby explaining why SEBF, itself a repressor, requires Pti4 for its repressing function.