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Plant Cell Advance Online Publication
Published on February 29, 2008; 10.1105/tpc.107.057752

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Received December 24, 2007
Returned for revision January 29, 2008
Accepted February 18, 2008

Potential Sites of Bioactive Gibberellin Production during Reproductive Growth in Arabidopsis

Jianhong Hu 1, Melissa G. Mitchum 1, Neel Barnaby 1, Belay T. Ayele 2, Mikihiro Ogawa 3, Edward Nam 1, Wei-Chu Lai 1, Atsushi Hanada 2, Jose M. Alonso 4, Joseph R. Ecker 4, Stephen M. Swain 3, Shinjiro Yamaguchi 2, Yuji Kamiya 2, and Tai-ping Sun 1*

1 Department of Biology, Duke University, Durham, North Carolina 27708
2 RIKEN Plant Science Center, Tsurumi-ku, Yokohama, Kanagawa 230-0045, Japan
3 CSIRO Plant Industry, Merbein, Victoria 3505, Australia
4 Plant Biology Laboratory, Salk Institute for Biological Studies, La Jolla, California 92037

* To whom correspondence should be addressed. E-mail: tps{at}duke.edu.

Gibberellin 3-oxidase (GA3ox) catalyzes the final step in the synthesis of bioactive gibberellins (GAs). We examined the expression patterns of all four GA3ox genes in Arabidopsis thaliana by promoter–{beta}-glucuronidase gene fusions and by quantitative RT-PCR and defined their physiological roles by characterizing single, double, and triple mutants. In developing flowers, GA3ox genes are only expressed in stamen filaments, anthers, and flower receptacles. Mutant plants that lack both GA3ox1 and GA3ox3 functions displayed stamen and petal defects, indicating that these two genes are important for GA production in the flower. Our data suggest that de novo synthesis of active GAs is necessary for stamen development in early flowers and that bioactive GAs made in the stamens and/or flower receptacles are transported to petals to promote their growth. In developing siliques, GA3ox1 is mainly expressed in the replums, funiculi, and the silique receptacles, whereas the other GA3ox genes are only expressed in developing seeds. Active GAs appear to be transported from the seed endosperm to the surrounding maternal tissues where they promote growth. The immediate upregulation of GA3ox1 and GA3ox4 after anthesis suggests that pollination and/or fertilization is a prerequisite for de novo GA biosynthesis in fruit, which in turn promotes initial elongation of the silique.




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