Figure 3.
Subcellular Localization of MBS1 under Normal Conditions and under 1O2 Stress.
(A) Localization of a Cr-MBS-YFP fusion protein in stably transformed C. reinhardtii cells. MBS is localized in the cytosol and the nucleus. YFP fluorescence, chlorophyll fluorescence, and the overlay of YFP fluorescence, chlorophyll fluorescence, and the bright-field image are shown. Bar = 3 µm.
(B) Localization of At-MBS1-GFP and At-MBS2-GFP fusion proteins in transiently transformed tobacco protoplasts. Both proteins are localized in the cytoplasm and the nucleus under nonstressed conditions. Images were obtained 48 h after protoplast transformation. Bars = 10 μm.
(C) At-MBS1 localizes to cytoplasmic SGs and PBs under 1O2 stress. AtMBS1-GFP was transiently coexpressed in tobacco protoplasts with either the SG marker Rbp47 or the PB marker Dcp1 (Weber et al., 2008). Colocalization in cytoplasmic foci was observed 30 min after induction of 1O2 stress by exposure to HL (500 µE m−2 s−1) in the presence of 1 µM MB. Note that PBs are much smaller than SGs, which is an observation that was consistently made in all protoplasts showing PB staining (cf. Supplemental Figure 3 online). The smaller size of the PBs correlates with lower levels of MBS1-GFP accumulation, possibly due to reduced stability of the protein molecules that are not incorporated into PBs. Bars = 10 μm.
(D) MBS1-associated cytoplasmic foci induced in cells of the upper epidermis by HL treatment (1000 µE m−2 s−1) for 3 h after 2 d of preincubation in the dark. The assays were performed with Arabidopsis seedlings that stably express the PMBS1:MBS1-GFP fusion gene in the mbs1-1 mutant background. Bars = 25 μm.
(E) Image from a movie of MBS1-associated cytoplasmic foci trafficking under 1O2 stress in PMBS1:MBS1-GFP/mbs1-1 seedlings (cf. Supplemental Movie 1 online). Bar = 25 μm.