Uncovering HEMERA-mediated Phytochrome Signaling Mechanisms in Arabidopsis

光是影响植物生长发育方方面面的环境信号之一，从种子萌发、叶绿体分化、光合作用到开花。虽然众所周知，光敏色素是介导大多数光反应的红光和远红光受体，但光敏色素的光激活和由此产生的形态反应之间的早期信号机制仍然是未知的。PI开发了一种新的遗传筛选方法，专门针对参与最早的光反应之一的信号成分，即细胞内光敏色素的运动。这种独特的遗传筛选鉴定了植物模式物种拟南芥中光敏色素信号的新成分HEMERA （HMR）。有趣的是，HMR是多个早期光敏色素信号事件所必需的，并且是叶绿体从前质体前体发育（叶绿体分化）所必需的第一个光敏色素信号成分。该研究旨在揭示hmr介导的导致光依赖性叶绿体分化的信号机制。具体目的是：(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)通过寻找能够恢复植物正常性状的突变来识别和表征HMR下游的成分，而HMI在其他方面没有功能。这个项目的结果可能对我们了解植物发育是如何受环境因素调节的基础知识有重大贡献。更好地了解这一过程将对提高作物产量和增强作物的农艺有益性状具有深远的意义。特别是，阐明叶绿体分化是如何由光引发的，将最终为科学家提高生物燃料作物的光合能力提供知识。此外，该项目将为博士后、研究生和本科生提供分子遗传学方法方面的优秀培训。

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.