Regulation of Arabidopsis HFR1 Activity in Light Signaling

Boyce Thompson Institute Plant Research, Ithaca NY

Investigators

Abstract

The sessile nature of plants demands a high degree of plasticity in their growth and development in response to the ambient environment, and light is one of the major environmental signals that controls many aspects of plant development. Arabidopsis seedling photomorphogenesis has been used as a model system for molecular genetic studies to dissect the mechanisms regulating light signaling in plants. Two blue/UV-A absorbing cryptochromes (cry1 and cry2) and five red/far-red light absorbing phytochromes (phyA-phyE) are the primary photoreceptors responsible for mediating Arabidopsis seedling photomorphogenesis. HFR1, a bHLH transcription factor, acts as a positive regulator in both phyA-mediated far-red and cry1-mediated blue light signaling. A regulatory mechanism of HFR1 activity was suggested by the observed physical interactions between HFR1 with COP1 and SPA1. COP1 is an E3 ubiquitin ligase targeting a subset of positive regulators of photomorphogenesis for degradation, thus repressing photomorphogenesis. SPA1 is a negative regulator of phyA signaling and is structurally related to COP1. It is hypothesized that COP1 ubiquitinates HFR1 in a process modulated by SPA1, and targets HFR1 for degradation via the 26S proteasome pathway, thus desensitizing light signaling. Experiments are designed to substantiate such a working hypothesis at the genetic, physiological and biochemical levels. The outcome of this research is expected to: 1) provide significant insights into the regulatory mechanisms of HFR1 function in both phyA and cry1 signaling, a better understanding of COP1 and SPA1 function, and the role of regulated proteolysis in regulating plant development in general; 2) provide guidance for genetic engineering to fine-tune light-responsive growth traits (such as height, leaf area, flowering time and sowing density) in crops of agronomic importance; 3) provide excellent training opportunities for scientists at different levels, including postdoctoral fellows, graduate and undergraduate/high school students/high school teachers, with a focus on the inclusion of underrepresented groups.