First published online November 14, 2002; 10.1104/pp.008581
Plant Physiol, December 2002, Vol. 130, pp. 2085-2094
Differential Regulation of RNA Levels of Gibberellin Dioxygenases
by Photoperiod in Spinach1
Dong Ju
Lee and
Jan A.D.
Zeevaart*
Department of Energy-Plant Research Laboratory (D.J.L., J.A.D.Z.),
and Department of Plant Biology (J.A.D.Z.), Michigan State University,
East Lansing, Michigan 48824-1312
Previous work with spinach (Spinacia oleracea) has
shown that the level of gibberellin (GA) 20-oxidase is strongly
up-regulated by long days (LD). In the present work, the effect of
photoperiod on expression of other GA dioxygenases was investigated and
compared with that of GA 20-oxidase. Two GA 2-oxidases and one GA
3-oxidase were isolated from spinach by reverse
transcription-polymerase chain reaction with degenerate primers and by
5'- and 3'-rapid amplification of cDNA ends. As determined by
high-performance liquid chromatography with on-line radioactivity
detection, the SoGA3ox1 gene product catalyzed
3 -hydroxylation of GA9 to GA4 and
GA20 to GA1. The SoGA2ox1 and
the SoGA2ox2 gene products catalyzed 2 -hydroxylation
of GA9 to GA51 and GA20 to
GA29. The product of GA20 metabolism by
SoGA3ox1 was identified as GA1 by gas chromatography-mass spectrometry, whereas the products of GA1 and
GA20 metabolism by SoGA2ox1 and SoGA2ox2 were identified as
GA8 and GA29, respectively. SoGA2ox1 also
metabolized GA53 to GA97. The levels of
SoGA20ox1 transcripts were greatly increased in all
organs tested in LD conditions, but the levels of
SoGA3ox1 transcripts were only slightly increased in
blades and petioles. A decrease in the levels of the
SoGA2ox1 transcripts in young leaves and tips in LD
conditions is opposite to the expression pattern of the
SoGA20ox1. Expression of SoGA20ox1 in
petioles and young leaves was strongly up-regulated by a supplementary
16 h of light, but the levels of SoGA3ox1 and SoGA2ox1 transcripts did not change. It is concluded
that regulation and maintenance of GA1 concentration in
spinach are primarily attributable to changes in expression of
SoGA20ox1.
1
This work was supported by the U.S. Department
of Agriculture (grant no. 97-35304-4692) and by the U.S. Department
of Energy (grant no. DE-FG02-91ER20021).
*
Corresponding author; e-mail zeevaart{at}msu.edu; fax
517-353-9168.
© 2002 American Society of Plant Biologists
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