The Subcellular Localization and Blue-Light-Induced Movement of Phototropin 1-GFP in Etiolated Seedlings of Arabidopsis thalianaw

Abstract

Phototropin 1 (phot1) is a photoreceptor for phototropism, chloroplast movement, stomatal opening, leaf expansion, and solar tracking in response to blue light. Following earlier work with PHOT1::GFP (Sakamoto and Briggs, 2002), we investigated the pattern of cellular and subcellular localization of phot1 in 3- 4-d-old etiolated seedlings of Arabidopsis thalinana. As expressed from native upstream sequences, the PHOT1::GFP fusion protein is expressed strongly in the abaxial tissues of the cotyledons and in the elongating regions of the hypocotyl. It is moderately expressed in the shoot/root transition zone and in cells near the root apex. A fluorescence signal is undetectable in the root epidermis, root cap, and root apical meristem itself. The plasma membranes of mesophyll cells near the cotyledon margin appear labeled uniformly but cross-walls created by recent cell divisions are more strongly labeled. The pattern of labeling of individual cell types varies with cell type and developmental stage. Blue-light treatment causes PHOT1::GFP, initially relatively evenly distributed at the plasma membrane, to become reorganized into a distinct mosaic with strongly labeled punctate areas and other areas completely devoid of fluorescence--a phenomenon best observed in cortical cells in the hypocotyl elongation region. Concomitant with or following this reorganization, PHOT1::GFP moves into the cytoplasm in all cell types investigated except for guard cells. It disappears from the cytoplasm by an unidentified mechanism after several hours in darkness. Neither its appearance in the cytoplasm nor its eventual disappearance in darkness is prevented by the translation inhibitor cycloheximide, although the latter process is retarded. We hypothesize that blue-light-induced phot1 re-localization modulates blue-light-activated signal transduction.

The Signal Transducer NPH3 Integrates the Phototropin1 Photosensor with PIN2-Based Polar Auxin Transport in Arabidopsis Root Phototropism

“…However, whether the phototropin photoreceptors (phots) are relevant to PIN2 cellular fate or whether PIN2 subcellular relocalization or degradation (or both) is involved in BL-induced root phototropism is unclear. In our previous study, we reported that the BL receptor phot1 is polarly localized on the PM of root cortical cells, showing a localization very similar to that of PIN2 (Rahman et al, 2010), and that the extent of BL-induced phot1 internalization reflects the intensity of BL administered (Wan et al, 2008). Based on these results, we postulated a relationship between BL-induced relocalization of phot1 and endosomal recycling of PIN2 protein.…”

“…Our results show that all lines have similar gravitropic bending Shaded areas are based on the early hypothesis , while bright areas are based on our results to explain PIN2 localization and dynamics in darkness and under BL illumination. Membrane-localized phot1 acts as a BL photoreceptor to activate the signal transducer scaffold protein NPH3 (Wan et al, 2008;Roberts et al, 2011). NPH3 plays role in switching the dynamic equilibrium of PIN2 between PVC-targeting trafficking and membrane-targeting recycling.…”

Higher plants use LOV to perceive blue light

“…Post-translational modification appears to modulate the subcellular localization of these photoreceptors [15,18,19]. In the dark, both phot1 and phot2 are tightly associated with the plasma membrane [18,19].…”

“…In the dark, both phot1 and phot2 are tightly associated with the plasma membrane [18,19]. How this is achieved remains to be elucidated, but the kinase domain of phot2 is sufficient for this localization [15,19].…”

“…How this is achieved remains to be elucidated, but the kinase domain of phot2 is sufficient for this localization [15,19]. Blue light triggers the relocalization of a fraction of phot1 to the cytoplasm, whereas a pool of phot2 relocalizes to the Golgi [18,19]. Interestingly, phot2 kinase activity seems to regulate internalization [15,19].…”