Involvement of a Ca(2+)-dependent protein kinase component downstream to the gibberellin-binding phosphoprotein, RuBisCO activase, in rice.
Previously, we reported the identification of a gibberellin (GA)-binding protein in rice using ligand binding assay that was homologous to RuBisCO activase (Komatsu et al., FEBS Lett. 384, 167-171, 1996). Here, we provide an evidence for the involvement of protein kinases components downstream to the GA-binding phosphoprotein, RuBisCO activase in rice. Ca(2+)-dependent protein kinase activity was studied in subcellular fractions of leaf sheath from transgenic rice containing sense and antisense constructs of RuBisCO activase. In-gel kinase assay using histone III-S as a substrate showed constitutive induction of a 46- and 48-kDa Ca(2+)-dependent protein kinase activity in the sense transgenic plants. Kinase activities of these proteins were significantly reduced in the presence of uniconazole, a potent GA biosynthesis inhibitor, but one of them was strongly promoted by GA(3) treatment in transgenic plants carrying a smaller subunit of RuBisCO activase (OsrcaA1) compared to the larger subunit OsrcaA2. Also, in vitro phosphorylation studies using two-dimensional polyacrylamide gel showed changes in the degree of phosphorylation of several proteins in OsrcaA1- and OsrcaA2-sense transgenic rice. These studies suggest the presence of two independent cytosolic Ca(2+)-dependent protein kinase signaling components downstream to the GA-binding protein in rice suggesting their role in GA signaling.
Sharma
Arun
A
Japan Science and Technology Corporation, Japan.
Komatsu
Setsuko
S
D002118:Calcium / Q000378:metabolism*; D015180:Electrophoresis, Gel, Two-Dimensional; D004790:Enzyme Induction / Q000187:drug effects; D005875:Gibberellins / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000494:pharmacology; D006657:Histones / Q000378:metabolism; D012275:Oryza / Q000187:drug effects / Q000201:enzymology*; D010766:Phosphorylation / Q000187:drug effects; D018515:Plant Leaves / Q000737:chemistry / Q000201:enzymology; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D030821:Plants, Genetically Modified / Q000187:drug effects / Q000201:enzymology; D011494:Protein Kinases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D021122:Protein Subunits; D015398:Signal Transduction / Q000502:physiology; D013347:Subcellular Fractions / Q000737:chemistry / Q000201:enzymology; D014230:Triazoles / Q000494:pharmacology
D005875:Gibberellins; D006657:Histones; D010940:Plant Proteins; D021122:Protein Subunits; D014230:Triazoles; C054765:rca protein, plant; D011494:Protein Kinases; C092705:uniconazole; D002118:Calcium