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DEVELOPMENT AND HORMONE ACTION

Gibberellin Regulation of Fruit Set and Growth in Tomato^1,[W]

Instituto de Biología Molecular y Celular de Plantas, Universidad Politécnica de Valencia-Consejo Superior de Investigaciones Científicas (J.C.S., R.S., O.R.-R., J.L.G.-M.), and Departamento de Biología Vegetal (M.F.), Universidad Politécnica de Valencia, 46022 Valencia, Spain

The role of gibberellins (GAs) in tomato (Solanum lycopersicum) fruit development was investigated. Two different inhibitors of GA biosynthesis (LAB 198999 and paclobutrazol) decreased fruit growth and fruit set, an effect reversed by GA₃ application. LAB 198999 reduced GA₁ and GA₈ content, but increased that of their precursors GA₅₃, GA₄₄, GA₁₉, and GA₂₀ in pollinated fruits. This supports the hypothesis that GA₁ is the active GA for tomato fruit growth. Unpollinated ovaries developed parthenocarpically in response to GA₃ > GA₁ = GA₄ > GA₂₀, but not to GA₁₉, suggesting that GA 20-oxidase activity was limiting in unpollinated ovaries. This was confirmed by analyzing the effect of pollination on transcript levels of SlCPS, SlGA20ox1, -2, and -3, and SlGA3ox1 and -2, encoding enzymes of GA biosynthesis. Pollination increased transcript content of SlGA20ox1, -2, and -3, and SlCPS, but not of SlGA3ox1 and -2. To investigate whether pollination also altered GA inactivation, full-length cDNA clones of genes encoding enzymes catalyzing GA 2-oxidases (SlGA2ox1, -2, -3, -4, and -5) were isolated and characterized. Transcript levels of these genes did not decrease early after pollination (5-d-old fruits), but transcript content reduction of all of them, mainly of SlGA2ox2, was found later (from 10 d after anthesis). We conclude that pollination mediates fruit set by activating GA biosynthesis mainly through up-regulation of GA20ox. Finally, the phylogenetic reconstruction of the GA2ox family clearly showed the existence of three gene subfamilies, and the phylogenetic position of SlGA2ox1, -2, -3, -4, and -5 was established.

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: José Luis García-Martínez (jlgarcim{at}ibmcp.upv.es).

^[W] The online version of this article contains Web-only data.

www.plantphysiol.org/cgi/doi/10.1104/pp.107.098335

^* Corresponding author; e-mail jlgarcim{at}ibmcp.upv.es.

Received February 20, 2007; accepted July 19, 2007; published July 27, 2007.

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