Separate functions for nuclear and cytoplasmic cryptochrome 1 during photomorphogenesis ofArabidopsisseedlings

Abstract

Cryptochrome blue-light receptors mediate many aspects of plant photomorphogenesis, such as suppression of hypocotyl elongation and promotion of cotyledon expansion and root growth. The cryptochrome 1 (cry1) protein of Arabidopsis is present in the nucleus and cytoplasm of cells, but how the functions of one pool differ from the other is not known. Nuclear localization and nuclear export signals were genetically engineered into GFP-tagged cry1 molecules to manipulate cry1 subcellular localization in a cry1-null mutant background. The effectiveness of the engineering was confirmed by confocal microscopy. The ability of nuclear or cytoplasmic cry1 to rescue a variety of cry1 phenotypes was determined. Hypocotyl growth suppression by blue light was assessed by standard end-point analyses and over time with high resolution by a custom computer-vision technique. Both assays indicated that nuclear, rather than cytoplasmic, cry1 was the effective molecule in these growth inhibitions, as was the case for the mechanistically linked membrane depolarization, which occurs within several seconds of cry1 activation. Petiole elongation also was inhibited by nuclear, but not cytoplasmic, cry1. Conversely, primary root growth and cotyledon expansion in blue light were promoted by cytoplasmic cry1 and inhibited by nuclear cry1. Anthocyanin production in response to blue light was strongly stimulated by nuclear cry1 and, to a lesser extent, by cytoplasmic cry1. An important step toward elucidation of cry1 signaling pathways is the recognition that different subcellular pools of the photoreceptor have different functions.blue light ͉ hypocotyl ͉ nuclear localization ͉ membrane depolarization ͉ anion channel

Subcellular partitioning-dependent functional switching of Arabidopsis photoreceptor phytochrome B in response to brassinosteroids

“…Here, we showed that the cytosolic and nuclear phyBs have opposite actions in seedling growth and gene expression in the seedling response to BR. A recent report (Wu and Spalding, 2007) that cryotochrome 1 shows separate nuclear and cytosolic functions in Arabidopsis seedling also support the notion. A spatially-differentiated function of a protein appears to be another layer of cellular regulation of a protein function.…”

Arabidopsis bZIP16 Transcription Factor Integrates Light and Hormone Signaling Pathways to Regulate Early Seedling Development

“…The blue light photoreceptors cryptochromes are also present in the nucleus (Wu and Spalding, 2007;Yu et al, 2007). Genetic screens have yielded many Arabidopsis thaliana mutants with aberrant photomorphogenic phenotypes (reviewed in Chory, 2010).…”

Formation of Nuclear Bodies of Arabidopsis CRY2 in Response to Blue Light Is Associated with Its Blue Light–Dependent Degradation

“…Arabidopsis CRY1 shuttles between the nucleus and cytosol, and it acts in both places (Cashmore et al, 1999;Wu and Spalding, 2007;Yu et al, 2007b), whereas CRY2 completes its posttranslational life cycle in the nucleus (Yu et al, 2007b). However, exactly where in the nucleus CRY2 performs its function and/or undergoes modification and degradation remains unclear.…”