Obligate Heterodimerization of Arabidopsis Phytochromes C and E and Interaction with the PIF3 Basic Helix-Loop-Helix Transcription Factor
Obligate Heterodimerization of Arabidopsis Phytochromes C and E and Interaction with the PIF3 Basic Helix-Loop-Helix Transcription Factor
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DOI：
10.1105/tpc.108.065227
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发表时间：
2009-03-01
期刊：
影响因子：
11.6
通讯作者：
Sharrock, Robert A.
中科院分区：
文献类型：
--
作者：
Clack, Ted;Shokry, Ahmed;Sharrock, Robert A.
光敏色素是调节植物对红光(R)和远红光（FR）光反应的二聚体色素蛋白。拟南芥基因组编码5种光敏色素载脂蛋白：I型phyya介导对FR的应答，II型phyB-phyE介导遮荫躲避和经典的R/FR可逆应答。在这项研究中，我们描述了同二聚体和异二聚体II型光敏色素的完整体内补体。出乎意料的是，phyC和phyE不同二聚体，在幼苗中仅与phyB和phyD作为异二聚体存在。含有phyC或phyE的异二聚体光敏色素在光调节下胚轴长度、叶面积和开花时间方面发挥了作用。phyC和无色phyB的异源二聚体是无活性的，这表明phyC亚基需要光谱完整的二聚体伴侣来激活自己。与phyC和phyE的专性异二聚化一致，phyC通过去除其phyB结合伙伴而变得不稳定，并且phyE的过表达导致phyE单体的积累。在红光脉冲下，phyA, phyB， phyC和phyD在体内与光敏色素相互作用因子3基本螺旋-环-螺旋转录因子相互作用，这种相互作用是FR可逆的。因此，大多数或所有I型和II型光敏色素，包括异二聚体形式，似乎通过pif介导的途径发挥作用。这些发现将植物R/FR光感受器结构的意想不到的多样性与建立的光敏色素信号传导机制联系起来。
Phytochromes are dimeric chromoproteins that regulate plant responses to red (R) and far-red (FR) light. The Arabidopsis thaliana genome encodes five phytochrome apoproteins: type I phyA mediates responses to FR, and type II phyB-phyE mediate shade avoidance and classical R/FR-reversible responses. In this study, we describe the complete in vivo complement of homodimeric and heterodimeric type II phytochromes. Unexpectedly, phyC and phyE do not homodimerize and are present in seedlings only as heterodimers with phyB and phyD. Roles in light regulation of hypocotyl length, leaf area, and flowering time are demonstrated for heterodimeric phytochromes containing phyC or phyE. Heterodimers of phyC and chromophoreless phyB are inactive, indicating that phyC subunits require spectrally intact dimer partners to be active themselves. Consistent with the obligate heterodimerization of phyC and phyE, phyC is made unstable by removal of its phyB binding partner, and overexpression of phyE results in accumulation of phyE monomers. Following a pulse of red light, phyA, phyB, phyC, and phyD interact in vivo with the PHYTOCHROME INTERACTING FACTOR3 basic helix-loop-helix transcription factor, and this interaction is FR reversible. Therefore, most or all of the type I and type II phytochromes, including heterodimeric forms, appear to function through PIF-mediated pathways. These findings link an unanticipated diversity of plant R/FR photoreceptor structures to established phytochrome signaling mechanisms.