Chloroplast differentiation, or how plants turn green after germination, is critical to the establishment of photosynthetic plastids that enable plant to undergo photosynthesis. Thus, it is an essential process during light-dependent plant development. Although it is well known that chloroplast differentiation is controlled mainly by the red and far-red photoreceptor phytochromes, little is known about the molecular mechanisms by which phytochromes initiate this process. Recently, the investigators identified a novel and essential component for phytochrome signaling, HEMERA (HMR), in the model plant species Arabidopsis. Interestingly, HMR is the first phytochrome signaling component discovered so far that is also required for chloroplast differentiation. HMR encodes a highly conserved protein in land plants, and was previously shown to be associated with plastidic transcriptional machinery. However, preliminary evidence from the investigators suggests that HMR should be localized in the nucleus. The research undertaken as part of this project aims to solve this dilemma, by determining the subcellular localization of HMR and to define its localization signals using a combination of genetics, biochemical, and cell biological approaches. The proposed research is likely to unravel novel mechanisms linking phytochrome signaling and the initiation of chloroplast differentiation. The elucidation of molecular mechanisms for chloroplast differentiation will contribute significantly to our basic knowledge of how nuclear and organellar genomes coordinate their responses to environmental cues, and will also have deep implications in improving yield in agriculture. In addition, the proposed projects will provide excellent training in molecular genetic approaches for postdoctoral fellows, graduate students, and undergraduate students.
