A gibberellin‐regulated protein phosphorylated by a putative Ca²⁺‐dependent protein kinase is G‐protein mediated in rice root

Abstract

The GA-signal transduction pathways downstream to the Ga a a a protein in rice seedling root were investigated using ingel kinase assay and in vitro protein phosphorylation techniques with a Ga a a a protein defective mutant, d1. A 50-kDa protein kinase was detected downstream to Ga a a a protein in the membrane fraction of rice seedling roots using an ingel kinase assay with histone III-S as a substrate. The activity of a 50-kDa protein kinase increased in the wild-type rice by gibberellin (GA 3 ) treatment, but did not change in the d1 mutant. This protein kinase activity was inhibited by the Ca 2 + chelator ethyleneglycol-bis-(beta-aminoethylether)-N , N , N 1 , N 1 -tetraacetic acid (EGTA), protein kinase inhibitors, staurosporine and H7, and calmodulin antagonist, trifluoperazine, suggesting that the 50-kDa protein kinase is a putative plant Ca 2 + -dependent protein kinase (CDPK). The activity of the 50-kDa putative CDPK reached its highest level at 3 h after GA 3 treatment and then gradually declined with time. In order to identify the endogenous substrate for 50-kDa putative CDPK, two-dimensional polyacrylamide gel electrophoresis followed by in vitro protein phosphorylation was carried out. The phosphorylation activity of an endogenous protein PP30, identified as an unknown protein having molecular weight 30 kDa and isoelectric point 5.8 was increased in the wild-type rice by GA 3 treatment, compared with the d1 mutant. The addition of GA 3 treated membrane fraction, which predominantly represent a 50-kDa putative CDPK further increased the phosphorylation of PP30. Almost similar to GA 3 treatment, phosphorylation activity of PP30 was also increased by the treatment with cholera toxin in the wild-type rice but not in d1 mutant. These results suggest that the 50-kDa putative CDPK and an unknown protein, PP30 promoted by GA 3 treatment are G-protein mediated in rice seedling roots.

Differential expression of rice calmodulin promoters in response to stimuli and developmental tissue in transgenic tobacco plants

“…OsCaM3 was responsive to SA and GA3. Plant growth and development have been reported to be regulated by SA and GA3 (7,9). This report along with our results demonstrated that CaM is involved in regulating plant development.…”

“…Among those, CaM has been identified as the highly conserved Ca 2＋ -binding protein in plants. In addition, CaM isoforms have been described in higher plants (7,8). The diversity observed in CaM isoforms has opened up avenues for investigation concerning their various functions, regulation, and evolution.…”

Repressing the Expression of the SUCROSE NONFERMENTING-1-RELATED PROTEIN KINASE Gene in Pea Embryo Causes Pleiotropic Defects of Maturation Similar to an Abscisic Acid-Insensitive Phenotype

“…The latter has Ca 21 -binding and second messenger activity. Others encode polygalacturonase inhibitor, a cell wall protein belonging to the Leu-rich repeat family with functions in development and defense (Di Matteo et al, 2003), and Ser/Thr protein kinase, putatively GA induced with a role in morphogenesis/embryogenesis (Khan et al, 2005). One EST encodes a Lec1-like transcription factor, which in Arabidopsis determines embryogenic identity and in Medicago is auxin up-regulated and associated with embryogenesis and morphogenesis (Kwong et al, 2003).…”

Expression profile of the α subunit of the heterotrimeric G protein in rice

“…1 This discovery has led to new questions regarding how rice Gα regulates cell number, and which other signaling molecules are involved in this process in various tissues and at different development stages. Studies of d1 suggest that rice Gα participates in both gibberellin signaling [2][3][4] and brassinosteroid signaling. [5][6][7][8] Promoter studies using the β-Glucuronidase (GUS) reporter indicate that Gα expression is highest in developing organs.…”