Complexome profiling of the Chlamydomonaspsb28mutant reveals THYLAKOID ENRICHED FRACTION 5 as an early photosystem II assembly factor

Abstract

Several auxiliary factors are required for the assembly of photosystem (PS) II, one of which is Psb28. While the absence of Psb28 in cyanobacteria has little effect on PSII assembly, we show here that the Chlamydomonaspsb28-null mutant is severely impaired in PSII assembly, showing drastically reduced PSII supercomplexes, dimers and monomers, while overaccumulating RCII, CP43modand D1mod. The mutant had less PSI and more Cytb6fand showed fewer thylakoid stacks and distorted chloroplast morphology. Complexome profiling of thepsb28mutant revealed that TEF5, the homolog of Arabidopsis PSB33/LIL8, co-migrated particularly with RCII. TEF5 also interacted with PSI. A Chlamydomonastef5null mutant is also severely impaired in PSII assembly and overaccumulates RCII and CP43mod. RC47 was not detectable in the light-growntef5mutant. Our data suggest a possible role for TEF5 in facilitating the assembly of CP47modinto RCII. Both thepsb28andtef5mutants exhibited decreased synthesis of CP47 and PsbH, suggesting negative feedback regulation possibly exerted by the accumulation of RCII and/or CP43modin both mutants. The strong effects of missing auxiliary factors on PSII assembly in Chlamydomonas suggest a more effective protein quality control system in this alga than in land plants and cyanobacteria.One-sentence summaryThe Chlamydomonas psb28 mutant is severely impaired in PSII assembly which via complexome profiling allowed identifying TEF5 as a novel PSII assembly factor that likely facilitates CP47 assembly.The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (https://academic.oup.com/plcell/pages/General-Instructions) is: Michael Schroda (m.schroda@rptu.de).