The BASIC PENTACYSTEIENE transcription factors interact with type-A Arabidopsis response regulators and regulate a sub-s

The type-A Arabidopsis Response Regulators (ARRs) are cytokinin primary response genes that negatively regulate the cytokinin signaling pathway. Here we identify members of the BASIC PENTACYSTIENE (BPC) transcription factor gene family as interacting with a subset of type-A ARR proteins in Arabidopsis thaliana and characterize their role in cytokinin signaling. Members of the BPC family interacted with type-A ARRs based on yeast two-hybrid and co-immunoprecipitation assays. bpc multiple mutants show reduced sensitivity to cytokinin in root elongation assays. The BPCs are necessary for induction of a subset of genes in response to exogenous cytokinin. Furthermore, a significant number of genes whose expression is altered in bpc mutant roots are also mis-expressed in cytokinin response factor (crf1,3,5,6) mutant and type-A arr3,4,5,6,7,8,9,15 mutant roots, suggesting interplay among these elements. BPC6 binds to the promoters of cytokinin-regulated genes and a significant number of BPC6 regulated-genes are also targets of the type-B ARR transcription factors, which are activated in response to cytokinin. These results suggest that the BPCs are part of a complex network of transcription factors that are involved in the response to cytokinin and the interaction of the BPCs with the type-A ARRs likely modifies this regulation.