Plants lacking the main light-harvesting complex retain photosystem II macro-organization

Abstract

Photosystem II (PSII) is a key component of photosynthesis, the process of converting sunlight into the chemical energy of life. In plant cells, it forms a unique oligomeric macrostructure in membranes of the chloroplasts¹. Several light-harvesting antenna complexes are organized precisely in the PSII macrostructure—the major trimeric complexes (LHCII)² that bind 70% of PSII chlorophyll and three minor monomeric complexes³—which together form PSII supercomplexes^4,5,6. The antenna complexes are essential for collecting sunlight and regulating photosynthesis^7,8,9, but the relationship between these functions and their molecular architecture is unresolved. Here we report that antisense Arabidopsis plants lacking the proteins that form LHCII trimers¹⁰ have PSII supercomplexes with almost identical abundance and structure to those found in wild-type plants. The place of LHCII is taken by a normally minor and monomeric complex, CP26, which is synthesized in large amounts and organized into trimers. Trimerization is clearly not a specific attribute of LHCII. Our results highlight the importance of the PSII macrostructure: in the absence of one of its main components, another protein is recruited to allow it to assemble and function.