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DEVELOPMENT AND HORMONE ACTION

Developmental and Hormonal Regulation of Gibberellin Biosynthesis and Catabolism in Pea Fruit^1,[OA]

Plant BioSystems, Department of Agricultural, Food, and Nutritional Science, University of Alberta, Edmonton, Alberta, Canada T6G 2P5

In pea (Pisum sativum), normal fruit growth requires the presence of the seeds. The coordination of growth between the seed and ovary tissues involves phytohormones; however, the specific mechanisms remain speculative. This study further explores the roles of the gibberellin (GA) biosynthesis and catabolism genes during pollination and fruit development and in seed and auxin regulation of pericarp growth. Pollination and fertilization events not only increase pericarp PsGA3ox1 message levels (codes for GA 3-oxidase that converts GA₂₀ to bioactive GA₁) but also reduce pericarp PsGA2ox1 mRNA levels (codes for GA 2-oxidase that mainly catabolizes GA₂₀ to GA₂₉), suggesting a concerted regulation to increase levels of bioactive GA₁ following these events. 4-Chloroindole-3-acetic acid (4-Cl-IAA) was found to mimic the seeds in the stimulation of PsGA3ox1 and the repression of PsGA2ox1 mRNA levels as well as the stimulation of PsGA2ox2 mRNA levels (codes for GA 2-oxidase that mainly catabolizes GA₁ to GA₈) in pericarp at 2 to 3 d after anthesis, while the other endogenous pea auxin, IAA, did not. This GA gene expression profile suggests that both seeds and 4-Cl-IAA can stimulate the production, as well as modulate the half-life, of bioactive GA₁, leading to initial fruit set and subsequent growth and development of the ovary. Consistent with these gene expression profiles, deseeded pericarps converted [¹⁴C]GA₁₂ to [¹⁴C]GA₁ only if treated with 4-Cl-IAA. These data further support the hypothesis that 4-Cl-IAA produced in the seeds is transported to the pericarp, where it differentially regulates the expression of pericarp GA biosynthesis and catabolism genes to modulate the level of bioactive GA₁ required for initial fruit set and growth.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Jocelyn A. Ozga (jocelyn.ozga{at}ualberta.ca).

^[OA] Open Access articles can be viewed online without a subscription.

www.plantphysiol.org/cgi/doi/10.1104/pp.108.132027

^* Corresponding author; e-mail jocelyn.ozga{at}ualberta.ca.

Received November 4, 2008; accepted March 9, 2009; published March 18, 2009.

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				E. Sundberg and L. Ostergaard Distinct and Dynamic Auxin Activities During Reproductive Development Cold Spring Harb Perspect Biol, December 1, 2009; 1(6): a001628 - a001628. [Abstract] [Full Text] [PDF]