Plants are sessile organisms that use solar energy to fuel their growth and development. The process plants use to convert solar energy into biologically useful forms of energy is called photosynthesis. Being immobile, plants must adapt to the ever-changing environment. To survive extremes in environmental variation, photosynthesis must be especially malleable and tightly controlled. Photosynthesis and much of the process of plant metabolism are performed in specialized cellular compartments called plastids. For plants to integrate fluctuating environmental signals with their intrinsic developmental programs, it is essential that plastids send information on the status of photosynthesis and other plastid-localized metabolism to other cellular compartments. Plastid signals regulate photosynthesis largely by controlling gene expression in the nucleus, the compartment of the plant cell that contains most of the plant genes. The goal of the proposed work is to identify and characterize the plastid signals and the plastid-to-nucleus signaling mechanisms that plants use to regulate the expression of nuclear genes active in photosynthesis.
This project will explore plastid-to-nucleus signaling that occurs during the development of chloroplasts, a specialized type of plastid that carries out photosynthesis. Previous studies indicate that at least two signaling pathways send information from plastids to the nucleus during the process of chloroplast development. Accumulation of a particular precursor of chlorophyll, the green pigment that plants use to harvest solar energy for photosynthesis, is a signal that regulates one of these pathways. However, the mechanism by which chlorophyll precursor accumulation within plastids is communicated to other cellular compartments is not understood. The two main objectives of this project are (1) to thoroughly characterize the role of GUN4, a recently-discovered chlorophyll precursor-binding protein, in plastid-to-nucleus signaling and the regulation of chlorophyll synthesis; and (2) to identify additional plastid signals and components of plastid-to-nucleus signaling pathways. The results from this work are expected to help us understand how plastid signals regulate the expression of nuclear genes with functions related to photosynthesis.
Broader educational and agricultural impact of the proposed work Because plastid development and function have a dramatic impact on the expression of many nuclear genes that encode proteins active in photosynthesis, the information generated by these experiments will begin to fill a significant gap in our understanding of plant growth and development and may be useful for rational genetic engineering of agronomically significant plants. Additionally, this project will provide training for undergraduate students, graduate students, and postdoctoral scientists. The results generated from this project will enhance the teaching activities of the project leader. This project will also contribute to the broad dissemination of knowledge at local, national, and international scientific meetings.
