Light influences many plant processes such as development, circadian responses including flowering, and growth. Plants are able to sense and to respond specifically to different wavelengths of light; red and far-red light are sensed by phytochromes, which are light-regulated serine and threonine kinases. Using a yeast two-hybrid screen, Kim et al. identified a protein phosphatase 2A catalytic subunit (from pea) that interacted with the Arabidopsis phytochrome A. The authors designated the phosphatase FyPP for flower-specific, phytochrome-associated protein phosphatase. In vitro, FyPP interacted with phytochrome A and B, with a preference for phytochrome B. When the phytochromes were pretreated with far-red light, they were designated Pfrs and FyPP had a preference for these. If Pfrs were not phosphorylated, they interacted more strongly with FyPP. Red light stimulates the translocation of phytochromes to the nucleus. Using a green-fluorescent protein fusion protein, the authors determined that FyPP was exclusively cytosolic. Thus, FyPP appears to interact specifically with the cytosolic Pfrs. In vitro phosphatase assays demonstrated that FyPP was able to dephosphorylate phytochrome A in the presence of Zn2+ or Fe2+ and that dephosphorylation occurred more quickly for the Pfr than for the red phytochrome (Pr). Overexpression of pea FyPP in Arabidopsis delayed flowering, whereas an antisense version produced plants that flowered earlier than wild-type plants. Thus, FyPP appears to be a negative regulator of the long-day flowering response.
D.-H. Kim, J.-G. Kang, S.-S. Yang, K.-S. Chung, P.-S. Song, C.-M. Park, A phytochrome-associated protein phsophatase 2A modulates light signals in flowering time control in Arabidopsis. Plant Cell 14, 3043-3056 (2002). [Abstract] [Full Text]