A Role for GIBBERELLIN 2-OXIDASE6 and Gibberellins in Regulating Nectar Production.

The secretion of floral nectar is tightly regulated by both developmental and temporal cues. Auxin and jasmonic acid were previously reported as having roles in regulating nectar production; however, the effects other phytohormones on this process are unknown. Here we report a role for gibberellins (GAs) in controlling nectar production in Arabidopsis thaliana. Specifically, we demonstrate that GA 2-OXIDASE6 (GA2ox6) is expressed in mature, secretory nectaries, and three independent ga2ox6 mutants display significant decreases in nectar production. On the other hand, overexpression of GA2ox6 in nectaries increases nectar output. These results suggest that elevated GA negatively impacts nectary function. This hypothesis is supported by the finding that known mutants with enhanced GA signaling also display a decrease in total nectar production, and that nectar output is restored to near wild-type levels in ga2ox6 flowers treated with the GA synthesis inhibitor paclobutrazol. Further, ga2ox6 flowers display a downregulation in the expression of genes involved in nectar production, as well as a significant decrease in the nectary auxin response. Cumulatively, these results strongly suggest that GA negatively regulates nectary function via control of the auxin response pathway.