Cytokinin signals via a two-component pathway that culminates in activation of the type-B response-regulator transcription factors.Based on genetic analysis, the type-B response regulators ARR1, ARR10, and ARR12 are the major contributors to cytokinin responses in the root.Whereas single mutants have minimal affects on cytokinin sensitivity, higher order mutants show pronounced effects consistent with overlapping function.For example, an arr1 arr12 mutant has a longer root than wild-type seedlings when treated with cytokinin.