Blue light receptor cryptochrome-Intracellular localization and signal transduction

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Cryptochromes are blue light receptors regulating development in plants. Though Arabidopsis cryptochrome 1 (AtCRY1) has been reported to be localized in nucleus, this characteristic is not entirely conserved among those from a variety of plant species. In this study it was shown that most molecules of rice cryptochrome 1 is localized to nucleus but at least a small aliquot is localized to cytoplasm. To determine the relationship between intracellular localization and function of cryptochrome, we constructed a GFP-OsCRY1 gene and examined the activity in transgenic Arabidopsis plants (hy4 mutant background). GFP-OsCRY1 plants showed shorter hypocotyls under blue light condition. By the addition of nuclear localization signal (NLS) on the amino-terminal of GFP-OsCRY1, the enhanced inhibition of hypocotyl elongation was observed specifically under blue light. On contrast, the addition of nuclear export signal (NES) abolished the inhibitive effect of OsCRY1 overexpression. Thus, our results suggest that cryptochromes are imported into nucleus and function there, at least in the inhibition of hypocotyl elongation.