ABSTRACT
Casein kinase1 (CK1) plays crucial roles in regulating growth and development via phosphorylating various substrates throughout the eukaryote kingdom. Blue light is crucial for normal growth of both plants and animals, and blue light receptor cryptochrome2 (CRY2) undergoes blue light-dependent phosphorylation and degradation in planta. To study the function of plant CK1s, systematic genetic analysis showed that deficiency of two paralogous Arabidopsis thaliana CK1s, CK1.3 and CK1.4, caused shortened hypocotyls, especially under blue light, while overexpression of either CK1.3 or CK1.4 resulted in the insensitive response to blue light and delayed flowering under long-day conditions. CK1.3 or CK1.4 act dependently on CRY2, and overexpression of CK1.3 or CK1.4 significantly suppresses the hypersensitive response to blue light by CRY2 overexpression. Biochemical studies showed that CK1.3 and CK1.4 directly phosphorylate CRY2 at Ser-587 and Thr-603 in vitro and negatively regulate CRY2 stability in planta, which are stimulated by blue light, further confirming the crucial roles of CK1.3 and CK1.4 in blue light responses through phosphorylating CRY2. Interestingly, expression of CK1.3 and CK1.4 is stimulated by blue light and feedback regulated by CRY2-mediated signaling. These results provide direct evidence for CRY2 phosphorylation and informative clues on the mechanisms of CRY2-mediated light responses.
Subject(s)
Arabidopsis Proteins/genetics , Casein Kinase I/genetics , Cryptochromes/genetics , Light , Signal Transduction , Amino Acid Sequence , Arabidopsis/genetics , Arabidopsis/metabolism , Arabidopsis/radiation effects , Arabidopsis Proteins/metabolism , Casein Kinase I/classification , Casein Kinase I/metabolism , Cotyledon/genetics , Cotyledon/metabolism , Cryptochromes/metabolism , Flowers/genetics , Flowers/metabolism , Flowers/radiation effects , Gene Expression Regulation, Plant/radiation effects , Hypocotyl/genetics , Hypocotyl/metabolism , Immunoblotting , Luminescent Proteins/genetics , Luminescent Proteins/metabolism , Microscopy, Confocal , Models, Genetic , Molecular Sequence Data , Mutation , Phosphorylation , Phylogeny , Plant Leaves/genetics , Plant Leaves/metabolism , Plants, Genetically Modified , Reverse Transcriptase Polymerase Chain Reaction , Sequence Homology, Amino Acid , Serine/genetics , Serine/metabolism , Threonine/genetics , Threonine/metabolismABSTRACT
The function of the gene gilgamesh (89B9-12) encoding a casein kinase in Drosophila spermatogenesis was studied. The chimeric Gilgamesh-GFP protein in spermatocytes is cortically located. In the polar and apolar spermatocytes, it concentrates at the terminal ends of the fusome, the organelle that passes through the system of ring canals of the spermatocyte cyst. At the stage of spermatid elongation, the protein associates with the nucleus. A spot of the highest Gilgamesh-GFP concentration in the nucleus co-localizes with gamma-tubulin in the basal body. At later stages, Gilgamesh is localized to the individualization complex (IC), leaving the nuclei somewhat before the IC investment cones, as detected by actin binding. The sterile mutation due to the gilgamesh gene leads to the phenotype of scattered nuclei and altered structure of actin cones in the individualizing spermatid cyst. Ultrastructural evidence confirmed defective spermatid individualization due to the mutation. The phylogenetic origin of the protein, and the connection between vesicular trafficking and spermatid individualization, are discussed.