FRIMP1 and FRIMP2: novel membrane proteins required for light-regulated development of Arabidopsis

植物对光环境的反应能力对其生存至关重要。光控制着植物生长发育的许多方面，在植物的整个生命周期中都很重要。光照调节下的响应包括萌发、绿色发育、光合作用幼苗、植物结构调节和开花时间控制。所有这些过程都对农业生产力至关重要，了解它们如何受到监管具有重大的长期重要性。植物有一系列的光感受器，包括吸收红光(R)和远红光（FR）的光敏色素，以及对蓝光/UVA有反应的隐色素和光促素。我们对植物对光的反应的了解大多来自于对模式植物拟南芥的研究，拟南芥有五种光敏色素。这些光敏色素如何传递它们的光信号来调节植物的发育是近年来人们非常感兴趣的一个领域。我们现在知道，在光线下，所有光敏色素都从细胞质转移到细胞核，细胞核是包含细胞大部分遗传信息的细胞器。一旦进入细胞核，它们与许多信号蛋白相互作用，改变许多基因的表达，从而导致植物生长和发育的变化。然而，这并不是故事的全部，还有一些生化和生理学证据表明光敏色素向细胞质和细胞膜中的蛋白质发出信号。迄今为止，尽管没有直接的遗传证据支持膜蛋白在光敏色素调控植物发育中的作用。我们试图通过识别和表征在植物发育的光调节中起作用的膜蛋白来解决这种异常。为了做到这一点，我们首先通过检查拟南芥中所有光调节基因的数据集确定了可预测的光调节膜蛋白基因。使用这种方法，我们已经确定了一些膜转运基因，似乎在幼苗发育中起作用。我们还发现了一些功能未知的膜蛋白，其中之一是FR光诱导膜蛋白，我们称之为FRIMP1。FRIMP1及其相近的对应物FRIMP2似乎对拟南芥幼苗发育和叶片发育都很重要。我们已经鉴定出缺乏frimp1和frimp2蛋白的突变体，这些突变体在FR光下显示出较长的下胚轴，在R光下显示出较大的子叶，这表明frimp1和frimp2是这些植物组织在光照下正常发育所必需的。有趣的是，FRIMP蛋白是一个全新的膜蛋白家族的成员，在包括人类在内的所有多细胞真核生物中都有近亲。由于它们还没有在任何这些生物中被研究过，我们在植物中了解到的它们可能具有更广泛的意义。该项目的主要目的是通过确定FRIMP1和FRIMP2调节的所有生理过程及其位置来了解它们对光的响应功能。我们将通过详细检查frimp1和frimp2突变体的生理反应，我们生产的frimp1和frimp2双突变体，以及人为增加frimp1和frimp2蛋白水平的植物来做到这一点。这将告诉我们FRIMP1和FRIMP2参与的所有反应。我们还将确定哪些基因在frimp1和frimp2突变体中表达改变，并利用这些信息找出frimp1和frimp2如何与植物内不同的信号通路相互作用。最后，我们将使用两种类型的报告蛋白来显示FRIMP1和FRIMP2在植物中的位置以及它们在细胞中的位置。然后，我们将能够提出关于FRIMP1和FRIMP2如何在分子水平上起作用的可测试假设。

The ability of a plant to respond to its light environment is critical to its survival. Light controls many aspects of plant growth and development and is important throughout the plant life cycle. Examples of responses under the regulation of light include germination, the development of green, photosynthesizing seedlings, regulation of the architecture of the plant and control of flowering time. All of these processes are crucial to agricultural productivity and an understanding of how they are regulated has great long-term importance. Plants have a range of photoreceptors that perceive light including the phytochromes that absorb red (R) and far-red (FR) light and the cryptochromes and phototropins that respond to blue/UVA. Much of what we know about how plants respond to light has come from studies on the model plant Arabidopsis thaliana that has five phytochromes. How these phytochromes pass on their light signal to regulate plant development has been an area of great interest in recent years. We now know that in light all phytochromes relocate from the cytoplasm of the cell to the nucleus, the organelle that contains the majority of the cell's genetic information. Once in the nucleus they interact with a number of signalling proteins to change the expression of many genes that lead to changes in plant growth and development. However, this is not the full story, and there is also some biochemical and physiological evidence that phytochrome signals to proteins in the cytoplasm and in cellular membranes. To date though there is little direct genetic evidence to back up a role for membrane proteins in phytochrome regulation of plant development. We have attempted to address this anomaly by trying to identify and characterize membrane proteins with a role in light regulation of plant development. To do this we have first identified predicted membrane protein genes that are light regulated by examining data sets of all light-regulated genes in Arabidopsis. Using this approach we have identified a number of membrane transporter genes that appear to have a role in seedling development. We have also identified some membrane proteins of unknown function and one of these is a FR light-induced membrane protein we have called FRIMP1. FRIMP1 and its close counterpart, FRIMP2, appear to be important for both seedling development and leaf development in Arabidopsis. We have identified frimp1 and frimp2 mutants that lack the FRIMP1 and FRIMP2 proteins and these mutants show a long hypocotyl under FR light and large cotyledons under R light, indicating that FRIMP1 and FRIMP2 are required for normal development of these plant tissues in the light. Interestingly, the FRIMP proteins are members of a completely new membrane protein family with close relatives in all multicellular eukaryotes including humans. As they have not been investigated in any of these organisms, what we learn about them in plants may be of much broader significance. The main aim of this project is to understand the function of FRIMP1 and FRIMP2 in response to light by determining all of the physiological processes they regulate and where they are located. We will do this by examining in detail the physiological responses of the frimp1 and frimp2 mutants, a frimp1frimp2 double mutant we have produced, and plants in which the levels of FRIMP1 and FRIMP2 proteins have been artificially increased. This will tell us the full range of responses in which FRIMP1 and FRIMP2 are involved. We will also determine what genes show altered expression in frimp1 and frimp2 mutants and use this information to find out how FRIMP1 and FRIMP2 interact with different signalling pathways within the plant. Finally, we will use two types of reporter proteins to show where FRIMP1 and FRIMP2 are located in the plant and also where they are within the cell. We will then be in a position to develop testable hypotheses about how FRIMP1 and FRIMP2 function at the molecular level.