From photons to genes - the molecular mechanisms of plant responses to red light

Bob Sharrock, Department of Plant Sciences, Montana State University, Bozeman, MT

The phytochromes are family of plant photoreceptors that control growth and development in response to environmental red/far-red (R/FR) light cues. Phytochrome signaling is initiated by light-induced conformational changes, followed by re-localization of the receptor to the nucleus and interaction with a large number of partner proteins, including putative transcription factors. In Arabidopsis, five phytochromes, phyA-phyE, are expressed in developmentally-regulated and tissue-specific patterns. These fall into two functionally distinct groups: phyA, which senses very low levels of light and continuous FR, and phyB-phyE, which sense long term R and the ratio of R:FR. Previous evidence has lead to the notion that the phytochromes are present in plants as homodimers and, therefore, that their individual activities can be determined by isolating monogenic phyA-phyE mutants. We have shown that several heterodimeric species of phytochrome form in plants, demonstrating that the phytochrome photoreceptor array is more complex and diverse than previously thought. On the other end of the signaling pathway, the outputs of R/FR light activation of phytochrome include changes in the expression of as many as 10% of the genes in a plant. The availability of a complete genome sequence for Arabidopsis has made possible many types of global approaches to understanding plant gene expression. Recent efforts to characterize light-induced changes in the proteome, the collection of all proteins present in an organism, using 2-dimensional gel electrophoresis will be described.