PLANT PHYSIOLOGY , Vol 113, Issue 4 1273-1282, Copyright © 1997 by American Society of Plant Biologists
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GENE REGULATION AND MOLECULAR GENETICS |
Involvement of Protein Kinase and Extraplastidic Serine/Threonine Protein Phosphatases in Signaling Pathways Regulating Plastid Transcription and the psbD Blue Light- Responsive Promoter in Barley
D. A. Christopher, L. Xinli, M. Kim and J. E. Mullet
Department of Plant Molecular Physiology, College of Tropical Agriculture and Human Resources, University of Hawaii at Manoa, St. John 503, Honolulu, Hawaii 96822 (D.A.C., L.X.)
We investigated the signaling pathways that control changes in plastid
transcription in response to development and light. Plastid gene expression
was analyzed in dark-grown barley (Hordeum vulgare L.) seedlings treated in
vivo with an inhibitor of protein phosphatases 1 and 2A, okadaic acid (OA),
or an inhibitor of protein kinases (K252a), followed by exposure of the
seedlings to either red, blue, or white light. OA prevented blue light from
activating the plastid psbD blue-light-responsive promoter (BLRP) and
prevented red and blue light from activating the expression of the
plastid-encoded rbcL and psbA and the nuclear-encoded RbcS and Lhcb genes.
OA reduced total plastid transcription activity in dark- and light-grown
seedlings by 77 to 80%, indicating that OA prevented light-responsive
transcription by reducing total plastid transcription. In contrast, K252a
activated the accumulation of mRNAs arising from the BLRP. Blue light in
combination with K252a increased psbD mRNA levels in an additive manner.
The results indicate that protein phosphatases 1 and/or 2A, which reside
external to the organelle, are required for proper function of plastid
transcription and chloroplast development, whereas a protein kinase
represses the BLRP in plants grown in the dark.