FIGURE 1.

The majority of thylakoid lumen proteins with experimentally verified roles are involved in the function of either the PSII complex or the PSI–NDH supercomplex. The most abundant protein families in the thylakoid lumen are the OEC and OEC-like proteins (green), the immunophilins (blue), and proteases (yellow). In addition, the lumen proteome comprises peroxidases (black), photoprotective enzymes (purple), and several auxiliary proteins. The OEC proteins are proposed to function in water oxidation (square boxes), granal stacking (bolded), photosystem assembly (dotted outline), strigolactone biosynthesis (circle box), and NDH-dependent cyclic electron transfer (dashed outline). A high proportion of lumen proteins are thioredoxin targets (underlined). Regulation of thylakoid redox reactions involves membrane-embedded and soluble proteins (dark blue), and other lumen proteins are also implicated (white typeface). Lumen proteins with phosphorylation sites (asterisked) may be regulated by TLP18.3 phosphatase. Based on current knowledge, verified components of lumenal NDH subcomplex are not under post-translational regulation. No characterized lumenal proteins have so far been linked to the function of ATP synthase.