Gibberellin Acts Positively Then Negatively to Control Onset of Flower Formation in Arabidopsis

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Science  09 May 2014:
Vol. 344, Issue 6184, pp. 638-641
DOI: 10.1126/science.1250498

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One Hormone, Two Phases

The switch from vegetative growth to flowering in the plant Arabidopsis involves two phases—inflorescence branching and flowering. Yamaguchi et al. (p. 638) examined how the phytohormone gibberellin regulates each phase differently. First, gibberellin levels increase and stimulate production of key flowering factors, one of which degrades gibberellin. As gibberellin levels then fall, the next phase of flowering factors is released from gibberellin repression. By regulating inflorescence branching separately from flowering, this system determines overall seed yield.


The switch to reproductive development is biphasic in many plants, a feature important for optimal pollination and yield. We show that dual opposite roles of the phytohormone gibberellin underpin this phenomenon in Arabidopsis. Although gibberellin promotes termination of vegetative development, it inhibits flower formation. To overcome this effect, the transcription factor LEAFY induces expression of a gibberellin catabolism gene; consequently, increased LEAFY activity causes reduced gibberellin levels. This allows accumulation of gibberellin-sensitive DELLA proteins. The DELLA proteins are recruited by SQUAMOSA PROMOTER BINDING PROTEIN–LIKE transcription factors to regulatory regions of the floral commitment gene APETALA1 and promote APETALA1 up-regulation and floral fate synergistically with LEAFY. The two opposing functions of gibberellin may facilitate evolutionary and environmental modulation of plant inflorescence architecture.

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