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Fruit growth and development depend on highly coordinated hormonal activities. The phytohormone gibberellin (GA) promotes growth by inducing degradation of the growth-repressing DELLA proteins; however, the extent to which DELLA proteins contribute to GA-mediated gynoecium and fruit development remains to be clarified. Here, we provide an in-depth characterization of the role of DELLA proteins in Arabidopsis thaliana fruit growth. We show that DELLA proteins are key regulators of reproductive organ size and important for ensuring optimal fertilization. We demonstrate that the seedless fruit growth (parthenocarpy) observed in della mutants can be directly attributed to the constitutive activation of GA signaling. It has been known for >75 years that another hormone, auxin, can induce formation of seedless fruits. Using mutants with complete lack of DELLA activity, we show here that auxin-induced parthenocarpy occurs entirely through GA signaling in Arabidopsis. Finally, we uncover the existence of a DELLA-independent GA response that promotes fruit growth. This response requires GIBBERELLIN-INSENSITIVE DWARF1-mediated GA perception and a functional 26S proteasome and involves the basic helix-loop-helix protein SPATULA as a key component. Taken together, our results describe additional complexities in GA signaling during fruit development, which may be particularly important to optimize the conditions for successful reproduction.

Original publication

DOI

10.1105/tpc.112.103192

Type

Journal article

Journal

Plant Cell

Publication Date

10/2012

Volume

24

Pages

3982 - 3996

Keywords

Arabidopsis, Arabidopsis Proteins, Basic Helix-Loop-Helix Transcription Factors, Flowers, Fruit, Gibberellins, Helix-Loop-Helix Motifs, Indoleacetic Acids, Plant Growth Regulators, Proteasome Endopeptidase Complex, Receptors, Cell Surface, Repressor Proteins, Reproduction, Signal Transduction, Transcription Factors