1. Col-0 cat2 pp2a-b'γ sid2 cat2sid2pp2a-b'γnpr1cat2 pp2a-b'γcat2 sid2pp2a-b'γ sid2cat2 nrp1 cat2 npr1 pp2a-b'γ sensCAT2 + revCAT2 sensCAT2 + LB1 sensNPR1 + revNPR1 + Digestion sensPP2A-B'γ + revPP2A-B'γ revPP2A-B'γ + LBa1 sensSID2 + revSID2 + Digestion 1000 bp 750 bp 250 bp 500 bp Fig. S1. Production and genotyping of Arabidopsis mutant lines (cat2 pp2a-b'γ, cat2 pp2a-b'γ sid2, cat2 npr1 pp2a-b'γ). The frame on the right indicates the size of the markers shown on the left lane of the main photograph.

2. Fig. S2. Ascorbate and glutathione contents in Arabidopsis mutants grown at moderate light in long days. Top, ascorbate. Bottom, glutathione. White blocks, reduced forms. Red blocks, oxidized forms. Numbers above the bars indicate % reduction. 9191 63858569% Col-0cat2 pp2a-b'  cat2 pp2a-b'  Col-0cat2 pp2a-b'  cat2 pp2a-b'  Leaf content (nmol·g -1 FW) Leaf content (µmol·g -1 FW) 968582 81%

3. Fig. S3. Conditional nature of cat2 pp2a-b'  interaction: Arabidopsis plants grown in low light (30 µmol·m -2 s -1 ) in long days do not show oxidative stress or lesions. (a) Photographs of plants. (b) Fresh weight. (c) Glutathione contents. Red blocks, GSSG. White blocks, GSH. Col-0cat2 cat2 pp2a-b'  pp2a-b'  Rosette FW (mg) Leaf glutathione (nmol·g -1 FW) Col-0 cat2 pp2a-b'  cat2 pp2a-b'  (a) (b) (c)

4. Fig. S4. General increases in free amino acid contents in cat2 pp2a-b'  Arabidopsis lines were grown and sampled in short days. In all frames, the column order is, from left to right: Col-0, cat2, pp2a-b'  cat2 pp2a-b' . Scaling shows relative contents after normalization to internal standard and sample fresh weight. *Significant difference from Col-0 at P<0.05. Primary nitrogen assimilation/remobilization/photorespiration Sulfur-containing amino acids and synthesis pathways Branched-chain amino acids GlutamateGlutamineAspartateAsparagineGlycineSerine Cysteine Arginine MethionineHomoserine IsoleucineLeucineValine Aromatic amino acids and synthesis PhenylalanineTyrosineTryptophan Others LysineGABA  -Alanine O-acetylserine Ornithine Shikimate Threonine * * * * * * * * * * ** * * * * * * * * * * * * *

5. Fig. S5. Pattern of phosphoproteins in total soluble and membrane fractions isolated from Arabidopsis wild type, cat2, pp2a-b'γ and cat2 pp2a-b'γ leaves grown and sampled in short days. Membrane (upper panels) and soluble (lower panels) fractions of Col-0, pp2a-b’γ, cat2 and cat2 pp2a-b'γ leaves were fractionated by one-dimensional SDSPAGE. Phosphoproteins were detected with ProQ Diamond (left panels), and total proteins were subsequently stained with Sypro Ruby (right panels). Samples corresponding to 80 μg of protein were loaded in each well.

6. cat2 pp2a-b' γ cat2 Col-0 pp2a-b' γ Number of days Number of leaves Fig. S6. Analysis of flowering time in Arabidopsis Col-0 and mutant lines (a). Number of days at flowering (stem length of 1 cm). (b) Number of leaves at flowering. Data are means of 30 plants growing in long days (16h light/8h dark). * and + indicate difference relative to Col-0 or to cat2 (P<0.05). + * + * + * + *