title: Photosystem I activity is increased in the absence of the PSI-G subunit.
abstract: PSI-G is a subunit of photosystem I in eukaryotes. The function of PSI-G was characterized in Arabidopsis plants transformed with a psaG cDNA in antisense orientation. Several plants with significantly decreased PSI-G protein content were identified. Plants with reduced PSI-G content were indistinguishable from wild type when grown under optimal conditions, despite a 40% reduction of photosystem I. This decrease of photosystem I was correlated with a similar reduction in state transitions. Surprisingly, the reduced photosystem I content was compensated for by a more effective photosystem I because the light-dependent reduction of NADP(+) in vitro was 48% higher. Photosystem I antenna size determined from flash-induced P700 absorption changes did not reveal any significant effect on the size of the photosystem I antenna in the absence of PSI-G, whereas a 17% reduction was seen in the absence of PSI-K. However, nondenaturing green gels revealed that the interaction between photosystem I and the light-harvesting complex I was less stable in the absence of PSI-G. Thus, PSI-G plays a role in stabilizing the binding of the peripheral antenna. The increased activity in the absence of PSI-G suggests that PSI-G could have an important role in regulation of photosystem I.
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: Lisa
authors.initials: L
authors.lastname: Rosgaard
authors.forename: Jurgen
authors.initials: J
authors.lastname: Knoetzel
authors.forename: Henrik Vibe
authors.initials: HV
authors.lastname: Scheller
mesh_terms: D017360:Arabidopsis / Q000235:genetics; D002461:Cell Line, Transformed; D002851:Chromatography, High Pressure Liquid; D018076:DNA, Complementary / Q000378:metabolism; D005822:Genetic Vectors; D015151:Immunoblotting; D008027:Light; D008856:Microscopy, Fluorescence; D009249:NADP / Q000378:metabolism; D016376:Oligonucleotides, Antisense / Q000378:metabolism; D045322:Photosynthetic Reaction Center Complex Proteins / Q000235:genetics*; D045331:Photosystem I Protein Complex; D010940:Plant Proteins / Q000235:genetics* / Q000502:physiology*; D030821:Plants, Genetically Modified; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D013696:Temperature; D020524:Thylakoids / Q000378:metabolism
chemical_list: D018076:DNA, Complementary; D016376:Oligonucleotides, Antisense; D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex; D010940:Plant Proteins; C074492:photosystem I, PSI-G subunit; D009249:NADP