title: Degradation of Arabidopsis CRY2 is regulated by SPA proteins and phytochrome A.
abstract: The UV-A/blue light photoreceptor crytochrome2 (cry2) plays a fundamental role in the transition from the vegetative to the reproductive phase in the facultative long-day plant Arabidopsis thaliana. The cry2 protein level strongly decreases when etiolated seedlings are exposed to blue light; cry2 is first phosphorylated, polyubiquitinated, and then degraded by the 26S proteasome. COP1 is involved in cry2 degradation, but several cop1 mutants show only reduced but not abolished cry2 degradation. SUPPRESSOR OF PHYA-105 (SPA) proteins are known to work in concert with COP1, and recently direct physical interaction between cry2 and SPA1 was demonstrated. Thus, we hypothesized that SPA proteins could also play a role in cry2 degradation. To this end, we analyzed cry2 protein levels in spa mutants. In all spa mutants analyzed, cry2 degradation under continuous blue light was alleviated in a fluence rate-dependent manner. Consistent with a role of SPA proteins in phytochrome A (phyA) signaling, a phyA mutant had enhanced cry2 levels, particularly under low fluence rate blue light. Fluorescence resonance energy transfer-fluorescence lifetime imaging microscopy studies showed a robust physical interaction of cry2 with SPA1 in nuclei of living cells. Our results suggest that cry2 stability is controlled by SPA and phyA, thus providing more information on the molecular mechanisms of interaction between cryptochrome and phytochrome photoreceptors.
authors: Department of Plant Physiology, Faculty of Biology, Philipps-Universität, D-35032 Marburg, Germany.
authors: Guido
authors: G
authors: Weidler
authors: Sven
authors: S
authors: Zur Oven-Krockhaus
authors: Michael
authors: M
authors: Heunemann
authors: Christian
authors: C
authors: Orth
authors: Frank
authors: F
authors: Schleifenbaum
authors: Klaus
authors: K
authors: Harter
authors: Ute
authors: U
authors: Hoecker
authors: Alfred
authors: A
authors: Batschauer
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism*; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism; D056931:Cryptochromes / Q000378:metabolism*; D031541:Fluorescence Resonance Energy Transfer; D008856:Microscopy, Fluorescence / Q000379:methods; D009154:Mutation; D051942:Phytochrome A / Q000235:genetics / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000235:genetics* / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; C103618:CRY2 protein, Arabidopsis; D018797:Cell Cycle Proteins; D056931:Cryptochromes; C497973:PHYA protein, Arabidopsis; D051942:Phytochrome A; C118571:SPA1 protein, Arabidopsis; D017346:Protein Serine-Threonine Kinases; C517423:SPA2 protein, Arabidopsis; C517425:SPA4 protein, Arabidopsis