Plants continuously monitor and respond developmentally to myriad informational light signals from the environment.

What are the molecular mechanisms involved in the perception, interpretation and transduction of those signals?

We are interested in understanding the molecular mechanism by which light regulates gene expression in plants. Our research program is focused on the phytochromes, the major and best-characterized family of plant regulatory photoreceptors. The photoreceptor molecule functions as a biological switch that, upon perception of the light signal, triggers changes in transcription which are detectable within 5 minutes of the stimulus.

The general strategy we have adopted toward this problem is fourfold:

1. to examine the phytochrome molecule for clues to its photosensory function and mechanism of action using structural analysis, phytochrome-defective mutants and overexpression of mutagenized phytochromes in transgenic Arabidopsis.
2. to study genes under phytochrome control to identify promoter DNA elements and transcription factors involved in induction or repression of expression.
3. to identify signal transduction pathway components between the photoreceptor and the genes it regulates using genetic and molecular approaches.
4. to dissect the primary transcriptional networks that orchestrate the expression of downstream genes responsible for elaborating light-regulated development, using oligonucleotide-microarray-based expression profiling.

Our data suggest that the phytochromes signal directly to photoresponsive genes by light induced translocation from the cytoplasm into the nucleus, followed by specific physical interaction with promoter-bound transcriptuion factors of the basic helix-loop-helix (bHLH) class. Data also suggests that genes encoding a master-set of diverse transcriptional regulators, that orchestrate downstream expression in the transcriptional network, are direct targets of this signaling pathway.

Recently, we have obtained evidence that light-induced activation of the phytochrome moleculed induces intranuclear phosphorylation of the bHLH transcription factor, PIF3, preceding its proteosome-mediated degradation. These data suggest that phy-induced phorphorylation of target proteins may represent the primary intermolecular signaling transaction of the activated photoreceptor