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Red-light-induced Signaling Pathway in Arabidopsis Roots.   M.L. Molas1, M.J. Correll 1, J.Z. Kiss1  1Dept. of Botany, Miami Univ., Oxford, OH

   Red light can affect different developmental and growth processes in roots, such as gravitropism, phototropism, and lateral root and root hair formation. Phytochromes are a family of red/far red light photoreceptors that play roles in sensing the light stimulus and transducing this signal downstream. Using a fusion protein of phyB and the reporter green fluorescent protein (GFP), researchers have shown nuclear import of all the members of the phytochrome family (phyA to phyE). Light induced accumulation of phytocromes in the nucleus results in the formation of speckles that is correlated with various physiological responses mediated by these photoreceptors. Once in the nucleus, phyA and phyB interact with the transcription factor-like protein PIF3, which binds to various G-box sequences required for the light-induced expression of a variety of genes. Up to 30 % of the genome in Arabidopsis, including the regulation of more than 26 cellular pathways is light dependent. Although many of the light regulated genes in hypocotyls have been defined, very few have been identified in roots. 

Here, we used a fusion protein consisting of full-length phyB and GFP to observe phyB cellular localization in intact root tissue. Consistent with previous studies, we found a red light dependent translocation of PHYB-GFP fusion protein to the nucleus in root columella cells. Studies using microarray analysis are in progress in order to identify the genes and pathways involved in the physiological events regulated by red light in roots.  (Financial support provided by NASA grant NCC2-1200)