title: The PSI-O subunit of plant photosystem I is involved in balancing the excitation pressure between the two photosystems.
abstract: PSI-O is a subunit of photosystem I in eukaryotes. The function of PSI-O was characterized in Arabidopsis plants using RNA interference. Several transformants with the psaO-RNAi construct were generated, and a high proportion of the plants contained only very little or virtually no residual PSI-O. Plants lacking PSI-O have a 50% reduction in state transitions indicating a role for PSI-O in the balancing of excitation energy between the two photosystems. PSI-H and -L have been shown previously to be involved in state transitions, and immunoblot analysis revealed that plants devoid of PSI-L or -H also have 80-90% reduction in the abundance of PSI-O. In contrast, down-regulation of PSI-O has no negative effect on the content of PSI-H and -L. The interaction between PSI-O and the PSI-L was confirmed by chemical cross-linking. A model of PSI is proposed in which PSI-L as the most ancient subunit is closest to the reaction center, and PSI-O is positioned close to PSI-L on the PSI-H/-L/-I side of the PSI complex. PSI-H, -L, -O, and possibly -I are all involved in forming a domain in PSI that is involved in the interaction with light-harvesting complex II.
authors.affiliation: Plant Biochemistry Laboratory, Department of Plant Biology, the Royal Veterinary and Agricultural University, Thorvaldsensvej 40, DK-1871 Frederiksberg C, Denmark. peje@kvl.dk
authors.forename: Poul Erik
authors.initials: PE
authors.lastname: Jensen
authors.forename: Anna
authors.initials: A
authors.lastname: Haldrup
authors.forename: Suping
authors.initials: S
authors.lastname: Zhang
authors.forename: Henrik Vibe
authors.initials: HV
authors.lastname: Scheller
mesh_terms: D017360:Arabidopsis / Q000378:metabolism; D003432:Cross-Linking Reagents / Q000494:pharmacology; D015536:Down-Regulation; D004591:Electrophoresis, Polyacrylamide Gel; D005822:Genetic Vectors; D015151:Immunoblotting; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry; D009249:NADP / Q000737:chemistry; D010641:Phenotype; D045331:Photosystem I Protein Complex / Q000737:chemistry*; D011312:Pressure; D011401:Promoter Regions, Genetic; D017434:Protein Structure, Tertiary; D034622:RNA Interference; D013050:Spectrometry, Fluorescence; D013696:Temperature; D020524:Thylakoids / Q000737:chemistry / Q000378:metabolism
chemical_list: D003432:Cross-Linking Reagents; D045342:Light-Harvesting Protein Complexes; D045331:Photosystem I Protein Complex; D009249:NADP