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Plant and Cell Physiology Advance Access published online on February 23, 2008
Plant and Cell Physiology, doi:10.1093/pcp/pcn024
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© The Author 2008. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org

Phytochrome-regulated PIL1 derepression is developmentally modulated

Yong-sic Hwang1,2 and Peter H. Quail1,*

1. Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720; and USDA/ARS-Plant Gene Expression Center, 800 Buchanan Street, Albany, CA 94710
2. Department of Bioscience and Biotechnology, Konkuk university, 1 Hwayang-dong, Gwangjin-gu, Seoul 143-701, Korea

*Corresponding author: Peter H. Quail, Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720; and USDA/ARS-Plant Gene Expression Center, 800 Buchanan Street, Albany, CA 94710, Tel: (510) 559-5910, Fax: (510) 559-5678, email: quail{at}nature.berkeley.edu


  Abstract

We define the photoresponsiveness, during seedling deetiolation, of PHYTOCHROME-INTERACTING FACTOR 3-LIKE 1 (PIL1), initially identified by microarray analysis as an early-response gene that is robustly repressed by first exposure to light. We show that PIL1 mRNA abundance declines rapidly, with a half-time of 15 min, to a new steady-state level, 10-fold below the initial dark level, within 45 min of first exposure to red light. Analysis of phy-null mutants indicates that multiple phytochromes, including phyA and phyB, impose this repression. Conversely, PIL1 expression is rapidly derepressed by subsequent far-red-irradiation of previously red-exposed seedlings. However, the magnitude of this derepression is modulated over time, in a biphasic manner, in response to increasing duration of preexposure to continuous-red light: (a) An early phase (up to about 6 h) of relatively rapidly increasing effectiveness of far-red reversal of repression, as declining phyA levels relieve initial Very Low Fluence-suppression of this response; and (b) A second phase (beyond 6 h) of gradually declining effectiveness of far-red-reversal, to only 20% of maximal derepression, within 36 h of continuous-red exposure, with no evidence of circadian modulation of this responsiveness, an observation in striking contrast to a previous report for entrained, green seedlings exposed to vegetative shade. These data, together with analysis of phytochrome-signaling mutants and overexpressors with aberrant deetiolation phenotypes, suggest that the second-phase decline in robustness of PIL1 derepression is an indirect consequence of the global developmental transition from the etiolated to the deetiolated state, and that circadian coupling of derepression requires entrainment.

Keywords: phytochrome - deetiolation - early response gene - derepression - PHYTOCHROME-INTERACTING FACTOR 3-LIKE 1 (PIL1)

(Received November 23, 2007; Accepted February 11, 2008)
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