Changes of PSII and PSI antenna and core protein levels. Proteins from control and Tl-treated white mustard leaves were separated by SDS-PAGE followed by immunodetection with antibodies against Lhcb1, Lhcb2, Lhca1 (antenna proteins) and D1, D2, CP43, PsbO, PsaA (core proteins). Samples were loaded on the equal amount of chlorophyll (0.25 ?g). Description of samples abbreviation as given in the legend to Fig. 3

Thylakoid protein phosphorylation and state transitions are disturbed after high light treatment in pgr6 background. a Total protein extracts of 4-week-old wild type (WT), pgr6-1, pgr6?2, sps2 and stn7/stn8 analysed by immunoblotting with anti-phosphothreonine antibody; the principal thylakoid phospho proteins are indicated on the right according to their size. Core photosystem II proteins D1 (PsbA) and D2 (PsbD) are indicated as a single band due to their poor resolution. Actin was used as a loading control. b Lhcb1 and Lhcb2 phosphorylation levels were visualised after separation on Phostag™-pendant acrylamide gels. The upper band corresponds to the phosphorylated form (p-), stn7/stn8 double mutant is a non-phosphorylated control. c Average transient of the variable room temperature chlorophyll fluorescence measured during the transition from red (660nm) supplemented with far-red light (720nm) state 1 to pure red light state 2 (n?=?4 independent pots containing 2–3 plants). The fluorescence curves from pgr6 and sps2 are shifted on the x-axis to allow visualising the FMST1 and FMST2 values. The x-axis time scale refers to the wild-type curve. d Calculated quenching related to state transition (qT?=?(FMST1?–?FMST2)/FM), expressed as the percentage of FM that is dissipated by the state 1 to state 2 transition, of wild type (WT), pgr6?1 and sps2 under moderate light (120?mol?m?2?s?1) (ML) and after 3?h of high light (500?mol?m?2?s?1) (HL). Whiskers and box plot shows the minimum, first quartile, median, average, third quartile and maximum of each dataset (n?=?4 biologically independent samples); p-values are calculated via a two-tailed Student’s t test. e STN7 phosphorylation level visualised after separation on Phostag™-pendant acrylamide gels. The upper band corresponds to the phosphorylated form (p-), a protein sample from stn7/stn8 double mutant was loaded as a control for the antibody specificity. Uncropped images of the membranes displayed in a, b and e are available as Supplementary Fig. 11. Data points for items c, d are available as Supplementary data 2

Chemical inhibition of CCD activity revealed how a ccr2 generated apocarotenoid signal transcriptionally represses HY5 and LHCB2 expression during photomorphogenesis.(A) Transcript levels of PIF3 and HY5 in WT, ccr2, ccr2 det1-154 and det1-154 de-etiolated seedlings growing on MS media + /- D15. (B) Representative western blot images showing PIF3 and HY5 protein levels in WT, ccr2, ccr2 det1-154 and det1-154 de-etiolated seedlings growing on MS media + /- D15. The membrane was re-probed using anti-Actin antibody as an internal loading control. (C) Protein and transcript levels of LHCB2 expression in WT and ccr2 de-etiolated seedlings growing on MS media + /- D15. (D) Model showing how ACS regulates HY5 and LHCB2 expression in ccr2. Images of seedlings represent are cotyledons are coloured green or yellow to reflect the delay in chlorophyll biosynthesis induced by ACS as evidenced in Figure 6c. De-etiolation of seedlings was performed by transferring 4-d-old etiolated seedlings to continuous light for 3 d to induce photomorphogenesis. Statistical analysis denoted as a star was performed by pair-wise t-test (p<0.05). Error bars represent standard error of means. Ctrl; Control; Ctrl, D15; chemical inhibitor of CCD activity.

Double mutant maintains thylakoid protein phosphorylation and state transitions after high light. (A) Total protein extracts of wild type (WT), abc1k1.1, -2, abc1k3.1, -2, and abc1k1/abc1k3.1, -2 light-exposed leaves were separated by SDS PAGE, transferred on nitrocellulose membrane and decorated with anti-phosphothreonine antibody. The main thylakoid phospho-proteins are indicated on the right according to their size. Core photosystem II proteins D1 (PsbA) and D2 (PsbD) are indicated together due their poor resolution. (B) The accumulation of the principal photosynthetic complexes was assessed using antibodies against specific subunits of each complex: anti-Lhcb2 for the major LHCII, anti-D1 (PsbA) for PSII, anti-PetC for cytochrome b6f, anti-PsaD and anti-PsaC for PSI, and anti-AtpC for ATP synthase. Actin signal is shown as a loading control. (C) Fluorescence quenching related to the state transitions (qT) of wild type (WT), abc1k1.1, -2, abc1k3.1, -2, and abc1k1/abc1k3.1, -2 under moderate light (120 ?mol of photons m–2 s–1) (ML) and after 3 h of high light (500 ?mol of photons m–2 s–1) (HL). qT was calculated from the maximal chlorophyll fluorescence measured after 10 min exposure to red light (660 nm) supplemented with far-red illumination (720 nm) “State 1” (FMST1) or to pure red light “State 2” (FMST2). Quenching related to state transition was calculated as qT = (FMST1 – FMST2)/FM. Each value represents the average of a pot containing 2–3 plants. Superscript letters are used to indicate statistically different groups (p < 0.05) by paired Student’s t-test.

Immunoblot analysis of the photosynthetic proteins on the basis of equal total Ponceau S dye stained blot with proteins from leaves of wild type plants and pap1 mutant grown on MS medium in Petri dishes for four weeks under a 16 h light/8 h dark photoperiod at 23 °C with 100 ?E m?2 s?1. Proteins were visualized by immunoblotting using antibodies specific for RbcL, PsaB, PsbD, AtpB, RpoB, AccD and Lhcb2.4 proteins.

Accumulation dynamics of photosynthesis-related proteins during de-etiolation.Three-day-old etiolated seedlings of Arabidopsis thaliana were illuminated for 0 hr (T0), 4 hr (T4), 8 hr (T8), 12 hr (T12), 24 hr (T24), 48 hr (T48), 72 hr (T72), and 96 hr (T96) under white light (40 µmol/m2/s). (A) Proteins were separated by SDS-PAGE and transferred onto nitrocellulose membrane and immunodetected with antibodies against PsbA, PsbD, PsbO, PetC, PsaD, PsaC, Lhcb2, AtpC, ELIP, POR, phyA, HY5, and ACTIN proteins. (B–C) Quantification of PsbA, PetC, and PsaC during de-etiolation. Heatmap (B) was generated after normalization of the amount of each protein relative to the last time point (T96). Graph (C) corresponds to the absolute quantification of proteins at T96. Error bars indicate ± SD (n = 3). Quantification of photosystem-related proteins during de-etiolation is detailed in Figure 6—figure supplement 1.Figure 6—source data 1.Quantitative data for immunoblot analysis.Quantitative data for immunoblot analysis.Quantification of photosynthesis-related proteins.(A) Immunodetection of PsbA, PetC, and PsaC during de-etiolation. Dilutions were used for the later time points to avoid saturation of the signal. (B) Different bands were detected by Amersham Imager program and quantified by Image QuantTL (Amersham). (C) Calibration curves were created using recombinant proteins (Agrisera). Calibration curve composition: PsbA 10 ng (A; lane a), 5 ng (b), 2.5 ng (c), and 1.25 ng (d); PetC 10 ng (e), 5 ng (f), 2.5 ng (g), and 1.25 ng (h); PsaC 3 ng (i), 1.5 ng (l), 0.75 ng (m), and 0.325 ng (n). Data indicate mean ± SD (n = 3–4). Raw data and calculations are shown in Figure 6—source data 1.

Abundance of photosynthetic proteins in leaves of WT and Rieske‐OE plants. (A) Immunodetection of Rieske, plastocyanin (PC), D1 subunit of PSII, PsaB subunit of PSI, AtpB subunit of ATP synthase, Lhcb2 subunit of LHCII and PsbS in leaf protein extracts loaded on leaf area basis. The quantity of the large subunit of Rubisco (RbcL) was estimated from Ponceau stained membranes immediately after transfer. A titration series of one of the WT samples (WT1) was used for relative quantification. (B) Quantification of immunoblots relative to WT. mean ± SE, n = 4 biological replicates for WT, n = 3 for transgenic lines. Asterisks indicate statistically significant differences between transgenic lines and WT (Tukey test, *p < 0.05, **p < 0.01. ***p < 0.001).