Light signaling in the basal land plants Physcomitrella patens and Marchantia polymorpha

在种子植物拟南芥中，E3泛素连接酶COP1/SPA是黑暗中抑制光信号所需的关键负调控因子。它控制着植物整个生命周期的生长发育，包括幼苗黄化、遮荫躲避和光周期开花。COP1/SPA复合体由COP1和SPA蛋白组成，它们在黑暗中协同泛素化光信号的正调节因子（主要是转录因子）。光照使COP1/SPA复合物失活，从而允许这些转录因子积累和光信号传导进行。虽然COP1/SPA的功能在拟南芥中得到了很好的表征，但对这些重要的光信号中间体的进化尚不清楚。COP1也存在于动物体内，这表明它有一个古老的起源。相比之下，SPA基因是绿色谱系所特有的，这表明COP1/SPA合作功能在绿色谱系中已经进化，可能将COP1的活性置于光的控制之下。COP1和SPA基因的同源物存在于苔藓植物小壶草和多形地豆中，这两种植物都是早期陆地植物的模式系统。我们的遗传分析表明，小立壶菌的SPA基因功能不同于那些已被充分表征的拟南芥。此外，与种子植物相比，小立小藻中的光信号与内源发育程序（如分生组织活性）的联系似乎更少。因此，比较分析两种苔藓植物（小壶藓和麻豆属）和种子植物的光信号将有助于我们了解陆地植物对光环境的适应反应的进化。我们将通过遗传学和生物化学相结合的方法来分析小壶菌和地香菌的COP1-和spa -样基因的功能。我们将重点关注以下主要问题：1)这些苔藓植物的COP1-和spa样蛋白在多大程度上相互合作，即相互需要才能发挥活性？2) COP1-和spa样蛋白在多大程度上与黑暗和光明下的信号相互关联？3)与苔藓植物COP1和/或SPA相互作用的转录因子的功能是什么，即苔藓植物和种子植物之间的输出响应在多大程度上是保守的。

In the seed plant Arabidopsis, the E3 ubiquitin ligase COP1/SPA is a key negative regulator required to suppress light signaling in darkness. It controls growth and development throughout the plant life cycle, including seedling etiolation, shade avoidance and photoperiodic flowering. The COP1/SPA complex consists of COP1 and SPA proteins which cooperate to ubiquitinate positive regulators of light signaling - mainly transcription factors - in darkness. Light exposure inactivates the COP1/SPA complex, thereby allowing these transcription factors to accumulate and light signaling to proceed. While COP1/SPA function is well characterized in Arabidopsis, nothing is known about the evolution of these essential intermediates of light signaling. COP1 also exists in animals, suggesting an ancient origin. SPA genes, in contrast, are specific to the green lineage, indicating that COP1/SPA cooperative function has evolved in the green lineage, possibly to place the activity of COP1 under the control of light. Orthologs of COP1 and SPA genes are present in the bryophytes Physcomitrella patens and Marchantia polymorpha, both model systems for early land plants. Our genetic analyzes demonstrate that SPA gene functions in Physcomitrella are distinct from those of their well-characterized Arabidopsis counterparts. Also, light signaling in Physcomitrella appears to be less interconnected with endogenous developmental programs (e.g. meristem activity) than in seed plants. Thus, a comparative analysis of light signaling in two bryophytes (Physcomitrella and Marchantia) and seed plants will greatly advance our knowledge on the evolution of adaptive responses to the light environment in land plants. We will analyze the functions of Physcomitrella and Marchantia COP1- and SPA-like genes through a combination of genetic and biochemical approaches. We will focus on the following main questions: 1) To what extent do COP1- and SPA-like proteins from these bryophytes cooperate, i.e. require each other for activity? 2) To what extent are COP1- and SPA-like proteins interconnected with signaling in darkness and in the light? 3) What are the functions of transcription factors interacting with bryophyte COP1 and/or SPA, i.e. to what extent are output responses conserved between bryophytes and seed plants.