Fig 2: Effect of UV-B and blue light (BL) on leaf transmittance in dark-adapted Arabidopsis leaves of wild-type (WT), uvr8, phot1, phot2, and phot1phot2 mutant plants. (A) Leaves were irradiated for 1 h with UV-B (violet boxes) of 3.3 or 20 µmol·m-2·s-1 or kept in darkness (black boxes). (B) Leaves were irradiated for 1 h with blue light (blue boxes) of 3.3 or 20 or 120 µmol·m-2·s-1 or kept in darkness (black boxes). The difference ?T between leaf transmittance after and before the treatment was measured for red light (660 nm). Plots in (A) and (B) share the dark controls. The leaves irradiated with UV-B and those irradiated with blue light were taken from the same batch of plants. Asterisks indicate statistically significant differences between means for WT and mutant lines (adjusted p values: *0.01 < p < 0.05, ***p < 0.001). Each box represents 12 measurements.

Fig 3: Amplitudes of transmittance changes ?T due to chloroplast movements in leaves illuminated with continuous blue light of increasing intensity (0.4–120 µmol m-2 s-1) in (A) sum mutants, (B) siz1 and mms21 ligase mutants, (C) phot1siz1 and phot1mms21 mutants and (D) phot2siz1 and phot2mms21 mutants. Asterisks indicate statistically significant differences between mutant lines and the control (phot1 for phot1mms21 and phot1siz1, phot2 for phot2mms21 and phot2siz1, the wild type for other lines), as tested with the Dunnett’s test (*P = 0.01–0.05; **P = 0.001–0.01). Error bars = SE. (E) Blue light-induced chloroplast arrangements in palisade cells of Arabidopsis leaves of wild-type, siz1, phot1, phot2, phot1siz1 and phot2siz1 plants. Leaves were kept in darkness or irradiated with blue light (LED 460 nm) of 1.6 or 120 µmol m-2 s-1 for 50 min. Chloroplast arrangements were then examined under a confocal microscope, using chlorophyll autofluorescence (633 nm excitation, 661–721 nm emission). Maximum intensity projections were calculated from Z-stacks, which spanned whole depth of the epidermis and palisade parenchyma, starting from the leaf upper surface. The fluorescence from chloroplasts located at the bottom of palisade cells is less intense due to attenuation of excitation light.

Fig 4: The sumoylation pattern of N-terminal fragments of c-Myc tagged PHOT1 and PHOT2. The Arabidopsis SUMO modification system was reconstituted in bacteria by simultaneous overexpression of E1 (AtSAE1b, AtSAE2), E2 (AtSCE1a) and either AtSUMO1, AtSUMO2, AtSUMO3 or AtSUMO5 (native GG or mutated AA variants). In some experimental variants, AtMMS21 or AtSIZ1 were also overexpressed. Phot fragments were purified using Ni-NTA and analyzed by Western blotting, with an anti-c-Myc antibody. In the negative control, only phot fragments were overexpressed in E. coli cells. Arrowheads mark positions of non-sumoylated (black) or sumoylated (white) phot fragments. The results are a representative of at least three independent repetitions.

Fig 5: Representative dephosphorylation profiles of phototropin2 after blue light exposure (120 µmol m-2 s-1 and 1h) in Arabidopsis wild-type and mutant (phot1 and rcn1) leaves. For further description, see the legend of Fig. 7. The results represent one of 3–4 independent biological replicates.