Plant and Cell Physiology, 2002, Vol. 43, No. 2 152-158
© 2002 Oxford University Press
Cloning of Gibberellin 3ß-Hydroxylase cDNA and Analysis of Endogenous Gibberellins in the Developing Seeds in Watermelon
1 National Research Laboratory of Plant Functional Genomics, Division of Molecular Life Science, Pohang University of Science and Technology, Pohang, 790-784 Korea 2 Frontier Research Program, The Institute of Physical and Chemical Research (RIKEN), Wako-Shi, Saitama, 351-0198 Japan
We have isolated Cv3h, a cDNA clone from the developing seeds of watermelon, and have demonstrated significant amino acid homology with gibberellin (GA) 3ß-hydroxylases. This cDNA clone was expressed in Escherichia coli as a fusion protein that oxidized GA9 and GA12 to GA4 and GA14, respectively. The Cv3h protein had the highest similarity with pumpkin GA 2ß,3ß-hydroxylase, but did not possess 2ß-hydroxylation function. RNA blot analysis showed that the gene was expressed primarily in the inner parts of developing seeds, up to 10 d after pollination (DAP). In the parthenocarpic fruits induced by treatment with 1-(2-chloro-4-pyridyl)-3-phenylurea (CPPU), the embryo and endosperm of the seeds were undeveloped, whereas the integumental tissues, of maternal origin, showed nearly normal development. Cv3h mRNA was undetectable in the seeds of CPPU-treated fruits, indicating that the GA 3ß-hydroxylase gene was expressed in zygotic cells. In our analysis of endogenous GAs from developing seeds, GA9 and GA4 were detected at high levels but those of GA20 and GA1 were very low. This demonstrates that GA biosynthesis in seeds prefers a non-13-hydroxylation pathway over an early 13-hydroxylation pathway. We also analyzed endogenous GAs from seeds of the parthenocarpic fruits. The level of bioactive GA4 was much lower there than in normal seeds, indicating that bioactive GAs, unconnected with Cv3h, exist in integumental tissues during early seed development.
3 Corresponding author: E-mail, genean@postech.ac.kr; Fax, +82-54-279-2199.
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