Light-regulated modification and nuclear translocation of cytosolic G-box binding factors in parsley.

Abstract

Functional cell-free systems may be excellent tools with which to investigate light-dependent signal transduction mechanisms in plants. By evacuolation of parsley protoplasts and subsequent silicon oil gradient centrifugation of lysed evacuolated protoplasts, we obtained a highly pure and concentrated plasma membrane-containing cytosol. Using GTand G-box DNA elements, we were able to demonstrate a specific localization of a pool of G-box binding activity and factors (GBFs) but not one of GT-box binding activity in this cytosolic fraction. The DNA binding activity of the cytosolic GBFs is modulated in vivo as well as in vitro by light and phosphorylation/dephosphorylation activities. The regulation of cytosolic G-box binding activity by irradiation with continuous white light and phosphorylation correlates with a lightmodulated transport of GBFs to the nucleus. This was shown by a GBF-antibody cotranslocation assay in permeabilized, cell-free evacuolated parsley protoplasts. We propose that a light-regulated subcellular displacement of cytosolic GBFs to the nucleus may be an important step in the signal transduction pathway coupling photoreception to light-dependent gene expression.

Discrete Domains Mediate the Light-Responsive Nuclear and Cytoplasmic Localization of Arabidopsis COP1

“…This result is consistent with immunological detection of phytochrome B in nuclear and cytoplasmic fractions (Sakamoto and Nagatani, 1996). The G-box binding factors (GBFs), which bind to the G-box DNA sequence elements present in the promoters of many light-regulated nuclear genes, also appear to partition between the cytoplasm and the nucleus (Harter et al, 1994), and the nuclear level of at least one GBF, GBF2, may be increased by blue light (Terzaghi et al, 1997). On the other hand, the nuclear level of the repressor of photomorphogenesis COP1 is diminished under light conditions in Arabidopsis.…”

“…Nucleocytoplasmic partitioning plays an important role in diverse cellular signaling processes and has been implicated in the regulation of photomorphogenesis in plants (Harter et al, 1994;von Arnim and Deng, 1994;Sakamoto and Nagatani, 1996;Terzaghi et al, 1997). For instance, the photoreceptor phytochrome B possesses C-terminal elements that can target GUS to the nucleus.…”

Molecular Interactions of GBF1 with HY5 and HYH Proteins during Light-mediated Seedling Development in Arabidopsis thaliana

“…GBF1, HY5, and HYH may be directly related to the subcellular shuttling of COP1 from nucleus to cytoplasm in response to the onset of light signal (23,43,44). Light might also regulate the subcellular localization of transcription factors through phosphorylation (45). One plausible mechanism might be that COP1 stabilizes GBF1 in the cytoplasm of light-grown seedlings, and nuclear translocation of this pool of GBF1 may be followed by GBF1-HY5 heterodimer formation based upon the light conditions and physiological necessities.…”

Signal transduction in the photocontrol of chalcone synthase gene expression*

“…light-dependent nuelear transport (Harter et al 1994a) and lighl-dependeiil prolein phosphorylalion in cytosolic preparations (Harier et al 1994b). An increase in UV-light-dependcnl CHS transcription is therefore independent of the vaeuolar compartment and can even be monitored in cell-free lysates of evacuolated protoplasts, indicating an inlaet signalling cascade from the receptor to ihe CHS promoter (Frohnmeyer et al 1994).…”