Abstract
Cytokinin is a plant hormone regulating plant morphogenesis through cell differentiation and proliferation. Early cytokinin signaling in Arabidopsis cells occurs through His-Asp phosphorelay from the cyrokinin receptors to the transcription-factor-type response regulators (type-B ARRs). ARR1 directly transactivats many cytokinin primary responsive genes (CPRGs). Each promoter region of CPRGs has many in vitro ARR1 recognition sequences ((A/G)GAT(C/T), ARR1-seq). Here, we tested contribution of each ARR1-seq preceding CPRGs on transactiation by ARR1 in vivo.
A type-A ARR, ARR6 is a CPRG diriectly transactivated by ARR1, is preceded by a 750-bp promoter region containing 5 copies of ARR1-seq. We constructed mutant ARR6 promoters which contains a base substitution within recognition sequences and then fused to the luciferase gene. Each of them was introduced into onion epidermal cells together with ARR1ΔDDK, generating constitutively active truncated ARR1 protein. As a result, we found that each ARR1-seq differently contributes to transactivation by ARR1 in vivo.
