Uncovering HEMERA-mediated Phytochrome Signaling Mechanisms in Arabidopsis

从种子萌发、叶绿体分化、光合作用到开花，光是调节植物生长和发育的几乎所有方面的最有影响力的环境信号之一。虽然光敏色素是一种红光和远红光受体，介导了大多数的光反应，但早期的信号机制将光敏色素的光激活与所产生的形态反应联系在一起，仍然难以捉摸。PI开发了一种新的遗传屏幕，专门针对参与最早的光反应之一的信号组件，即光敏色素在细胞内的运动。这一独特的遗传筛选在植物模式植物拟南芥中发现了一种新的光敏色素信号成分--HMERA(HMR)。有趣的是，HMR是多个早期光敏色素信号事件所必需的，并且是第一个光敏色素信号成分，对于叶绿体从其前质体前体(叶绿体分化)发育来说是必不可少的。这项研究旨在揭示HMR介导的导致光依赖性叶绿体分化的信号机制。其具体目标是：(1)确定光敏色素如何调节HMR；(2)确定HMR在细胞中的位置与光信号和叶绿体分化的关系；(3)通过寻找在HMI不起作用的植物中恢复正常性状的突变来识别和表征HMR下游的成分。这个项目的成果可以极大地帮助我们了解植物发育是如何受到环境线索的调控的。更好地理解这一过程将对提高作物产量和增强作物的农艺性状具有深远的影响。特别是，阐明光是如何启动叶绿体分化的，最终将为科学家提高生物燃料作物的光合作用能力提供知识。此外，该项目将为博士后研究员、研究生和本科生提供出色的分子遗传学方法培训。

Light is one of the most influential environmental cues regulating almost every facet of plant growth and development, from seed germination, chloroplast differentiation and photosynthesis, to flowering. Although it has been well known that phytochromes are red and far-red light receptors mediating most of the light responses, early signaling mechanisms linking light activation of phytochromes and the resulting morphological responses remain elusive. The PI developed a novel genetic screen specifically targeted at signaling components involved in one of the earliest light responses, the movement of phytochromes within the cell. This unique genetic screen identified a novel component for phytochrome signaling, HEMERA (HMR), in the plant model species Arabidopsis. Interestingly, HMR is required for multiple early phytochrome signaling events and is the first phytochrome-signaling component essential for the development of chloroplasts from their pro-plastid precursors (chloroplast differentiation). The research is aimed at uncovering HMR-mediated signaling mechanisms leading to light-dependent chloroplast differentiation. The specific aims are: (1) To determine how phytochromes regulate HMR; (2) To determine the location of HMR in cells in relationship to light signaling and chloroplast differentiation; (3) To identify and characterize components downstream of HMR by looking for mutations that restore normal traits in a plant where HMI is otherwise not functional. The outcomes of this project could contribute significantly to our basic knowledge of how plant development is regulated by environmental cues. A better understanding of this process will have profound implications in increasing yield and enhancing agronomically beneficial traits in crops. In particular, the elucidation of how chloroplast differentiation is initiated by light will ultimately provide the knowledge to facilitate scientists to improve photosynthetic capacity in biofuel crops. In addition, the project will provide excellent training in molecular genetic approaches for postdoctoral fellows, graduate students, and undergraduate students.