Journal Article

Functional Characterization of Phytochrome Autophosphorylation in Plant Light Signaling

Yun-Jeong Han, Hwan-Sik Kim, Yong-Min Kim, Ah-Young Shin, Si-Seok Lee, Seong Hee Bhoo, Pill-Soon Song and Jeong-Il Kim

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 51, issue 4, pages 596-609
Published in print April 2010 | ISSN: 0032-0781
Published online April 2010 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pcq025
Functional Characterization of Phytochrome Autophosphorylation in Plant Light Signaling

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  • Biochemistry
  • Molecular and Cell Biology
  • Plant Sciences and Forestry

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Plant phytochromes, molecular light switches that regulate various aspects of plant growth and development, are phosphoproteins that are also known to be autophosphorylating serine/threonine kinases. Although a few protein phosphatases that directly interact with and dephosphorylate phytochromes have been identified, no protein kinase that acts on phytochromes has been reported thus far, and the exact site of phytochrome autophosphorylation has not been identified. In this study, we investigated the functional role of phytochrome autophosphorylation. We first mapped precisely the autophosphorylation sites of oat phytochrome A (phyA), and identified Ser8 and Ser18 in the 65 amino acid N-terminal extension (NTE) region as being the autophosphorylation sites. The in vivo functional roles of phytochrome autophosphorylation were examined by introducing autophosphorylation site mutants into phyA-deficient Arabidopsis thaliana. We found that all the transgenic plants expressing the autophosphorylation site mutants exhibited hypersensitive light responses, indicating an increase in phyA activity. Further analysis showed that these phyA mutant proteins were degraded at a significantly slower rate than wild-type phyA under light conditions, which suggests that the increased phyA activity of the mutants is related to their increased protein stability. In addition, protoplast transfection analyses with green fluorescent protein (GFP)-fused phyA constructs showed that the autophosphorylation site mutants formed sequestered areas of phytochrome (SAPs) in the cytosol much more slowly than did wild-type phyA. These results suggest that the autophosphorylation of phyA plays an important role in the regulation of plant phytochrome signaling through the control of phyA protein stability.

Keywords: Autophosphorylation; Phytochrome; Phosphorylation; Protein degradation; SAPs

Journal Article.  8451 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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