The response to cytokinin is mediated in large part by alterations in the transcriptome. These changes in transcript level are regulated by transcription factors. The most important group of transcriptional regulators of the cytokinin response are the type-B response regulators. Functional analysis of knock-out mutants of the different type-B response regulators is hampered by the high level of redundancy among the eleven members of this protein family. In order to circumvent this problem, we generated a dominant repressor of the type-B ARRs by fusing the SRDX repressor domain to ARR1, one of the type-B ARRs, and expressing it under the control of a 35S promoter. The resulting plants showed all the hallmarks of the cytokinin deficiency syndrome (Heyl et al., 2008; Figure2A). Phenotypic and molecular analysis of the resulting plants indicated that most if not all of the cytokinin response is mediated via this class of transcription factors (Figure 2B, C). However, promoter deletion experiments showed that additional factors are involved in fine-tuning of the transcriptional response to cytokinin (Ramireddy et al, 2013). In addition several genetic screens identified several putative co-regulators of this signaling pathway and these are currently under investigation.