Mira-Rodado Virtudes, Sweere Uta, Grefen Christopher, Kunkel Tim, Fejes Erzsébet, Nagy Ferenc, Schäfer Eberhard, Harter Klaus
Zentrum für Molekularbiologie der Pflanzen/Pflanzenphysiologie, Universität Tübingen, Auf der Morgenstelle 1, D-72076, Tübingen, Germany.
J Exp Bot. 2007;58(10):2595-607. doi: 10.1093/jxb/erm087. Epub 2007 Jun 1.
The A-type response regulator ARR4 is an element in the two-component signalling network of Arabidopsis. ARR4 interacts with the N-terminus of the red/far-red light photoreceptor phytochrome B (phyB) and functions as a modulator of photomorphogenesis. In concert with other A-type response regulators, ARR4 also participates in the modulation of the cytokinin response pathway. Here evidence is presented that ARR4 directly modulates the activity state of phyB in planta, not only under inductive but also under extended irradiation with red light. Mutation of the phosphorylatable aspartate to asparagine within the receiver domain creates a version of ARR4 that negatively affects photomorphogenesis. Additional evidence suggests that ARR4 activity is regulated by a phosphorelay mechanism that depends on the AHK family of cytokinin receptors. Accordingly, the ability of ARR4 to function on phyB is modified by exogenous application of cytokinin. These results implicate a cross-talk between cytokinin and light signalling mediated by ARR4. This cross-talk enables the plant to adjust light reponsiveness to endogenous requirements in growth and development.
A 型响应调节因子 ARR4 是拟南芥双组分信号网络中的一个元件。ARR4 与红光/远红光光感受器光敏色素 B（phyB）的 N 端相互作用，并作为光形态建成的调节因子发挥作用。与其他 A 型响应调节因子协同作用时，ARR4 也参与细胞分裂素响应途径的调节。本文提供的证据表明，ARR4 在植物体内直接调节 phyB 的活性状态，不仅在诱导条件下，而且在红光延长照射下也是如此。在受体结构域内将可磷酸化的天冬氨酸突变为天冬酰胺会产生一种对光形态建成有负面影响的 ARR4 变体。更多证据表明，ARR4 的活性受一种依赖于细胞分裂素受体 AHK 家族的磷酸传递机制调控。因此，外源施加细胞分裂素会改变 ARR4 作用于 phyB 的能力。这些结果表明由 ARR4 介导的细胞分裂素和光信号之间存在相互作用。这种相互作用使植物能够根据生长和发育的内源性需求调整光响应性。
