The Activity of the Maize Opaque2 Transcriptional Activator Is Regulated Diurnally1
The maize ( Zea mays L.) Opaque2 (O2) protein is an endosperm-specific transcriptional activator whose DNA-binding activity is regulated diurnally by a phosphorylation/dephosphorylation mechanism. We show that the O2 transcript undergoes pronounced oscillations during the day-night cycle. The highes...
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Published in | Plant physiology (Bethesda) Vol. 121; no. 4; pp. 1321 - 1327 |
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Main Authors | , , , , |
Format | Journal Article |
Language | English |
Published |
American Society of Plant Physiologists
01.12.1999
|
Online Access | Get full text |
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Summary: | The maize (
Zea mays
L.) Opaque2 (O2) protein is an endosperm-specific transcriptional activator whose DNA-binding activity is regulated diurnally by a phosphorylation/dephosphorylation mechanism. We show that the
O2
transcript undergoes pronounced oscillations during the day-night cycle. The highest level of the
O2
message is present at midday and the lowest level at midnight. The level of
O2
transcript follows a diurnal rhythm that appears controlled by the circadian clock. Two different endosperm-expressed DNA-binding proteins, PBF (prolamin box-binding factor) and OHP1 (O2-heterodimerizing protein 1), were also analyzed. While the
PBF
message levels oscillate diurnally, the steady-state levels of
OHP1
transcript were constant through the day and night. We present data showing that the seed is not directly involved in the perception of the light signal, but presumably responds to diurnal fluxes of nutrients into the endosperm. Moreover, we show that the O2 protein is not involved in the regulation of its own transcript levels. These data indicate that
O2
activity is down-regulated at night by both a reduction in
O2
transcript and by hyperphosphorylation of residual O2 protein, and suggest that regulatory gene activity during endosperm development may be acutely sensitive to a diurnal signal(s) emanating from the plant and passing into the developing seeds. |
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Bibliography: | Corresponding author; e-mail rschmidt@ucsd.edu; fax 858–534–7108. |
ISSN: | 0032-0889 1532-2548 |