Gibberellins and Floral Induction in Arabidopsis

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The transition from vegetative growth to flowering is controlled both by environmental and endogenous cues. Understanding where and how these signals are integrated is a prerequisite for understanding why similar environmental or endogenous cues can elicit opposite flowering responses in different plants. For example, while the plant hormone gibberellin generally induces flowering in rosette plants such as Arabidopsis, it inhibits flowering of several other plants. Similarly, Arabidopsis flowers faster in long than in short days, while other plants flower preferentially, or even exclusively, in short days. Dr. Weigel proposes complementary biochemical, physiological, molecular and genetic approaches to determine how gibberellins induce flowering in Arabidopsis. He has shown that, in Arabidopsis, flowering signals converge on the promoter of the floral identity gene LEAFY. He has shown that the LEAFY promoter contains a gibberellin-response element that is essential for promoter activity in short days. He has also identified, by loss- and gain-of-function mutageneses, several FOG and GAT genes, which affect the gibberellin-requirement for flowering. He now proposes (1) to identify the factor that interacts with the LEAFY promoter to confer GA response; (2) to integrate the newly discovered FOG and GAT genes into the current framework of floral inductive pathways; (3) to study the molecular biology of the flowering-specific FOG1, FOG2 and GAT1-3 genes; and (4) to characterize in more detail FOG4, which strongly affects several gibberellin responses, including germination and flowering.The importance of flowers for human sustenance cannot be overstated. Not only are they organs of plant reproduction, but their immediate products are fruits and seeds, including cereal grains, which provide the majority of calories consumed by humans. Thus, understanding how plants regulate the formation of flowers is likely to have long-ranging practical applications. This research will serve as a starting point for understanding why flowering of different plants can respond in opposite ways to similar signals. The detailed mechanistic knowledge gained from the proposed studies will enable us in the future to fine tune flowering responses of important crop plants.