Fig. 1: Identification of the Chlorella sorokiniana linker protein (CsLinker).

a, TEM of the Chlamydomonas reinhardtii pyrenoid (n = 1, single observation), with adjacent schematic of Rubisco condensation in the pyrenoid by interaction of EPYC1 helices with the Rubisco small subunits (RbcSs). Condensed Rubisco fixes CO₂ to organic carbon. Scale bar, 1 μm. b, Phylogeny of Chlamydomonas, Chlorella and plants. Estimated divergence points from a time-calibrated phylogeny²⁸. c, Schematic representation of FLIPPer used to identify candidate linkers that share features with EPYC1. Where relevant, the programme used is indicated. The number of sequences remaining after each filtering step of the Chlorella sorokiniana UTEX1230 genome is indicated. pI, isoelectric point; res., residue; Φ, hydrophobic; ζ, electrostatic. d, Venn diagram demonstrating identification of CsLinker from FLIPPer and CsRbcL co-immunoprecipitation followed by mass spectrometry (co-IP). e, Reciprocal co-IP experiments performed using antibodies raised to the Rubisco large subunit (left) and CsLinker (right). Dashed lines indicate arbitrary significance thresholds (−log₁₀[adjusted P value] > 4, log₂[fold change] > 4), above which points are sized according to their summed intensity (M, millions) following the inset key, from 3 biological replicates. f, Predicted secondary structure of CsLinker from AlphaFold modelling (Supplementary Fig. 1). The predicted chloroplast transit peptide (cTP) and α-helices (α1–6) are indicated. g, Primary sequence alignment of the six repeat regions of CsLinker, coloured by residue property.