Gibberellins signal nuclear import of PHOR1, a photoperiod-responsive protein with homology to Drosophila armadillo

S. tuberosum ssp. andigena potato plants require short days (SD) for tuberi zation. We have isolated PHOR1 (photoperiod-responsive 1), which shows upre gulated expression in induced leaves (SD). PHOR1 encodes an arm repeat prot ein with homology to the Drosophila segment polarity protein armadillo. Ant isense inhibition of PHOR1 produces a semidwarf phenotype similar to that o f GA-deficient plants, and the antisense lines show reduced GA responsivene ss combined with a higher endogenous GA content than wild-type plants. Feed back regulation of GA biosynthetic genes is also altered in these lines. Co nversely, transgenic lines overexpressing PHOR1 show an enhanced response t o GA. GA application induces rapid migration of PHOR1-GFP protein to the nu cleus. Thus, PHOR1 appears to be a general component of GA signaling pathwa ys that relocalizes to the nucleus in the presence of GA.