TAILIEUCHUNG - Báo cáo khoa học: Knock-out of the chloroplast-encoded PSI-J subunit of photosystem I in Nicotiana tabacum PSI-J is required for efficient electron transfer and stable accumulation of photosystem I

The plastid-encodedpsaJgene encodes a hydrophobic low-molecular-mass subunit of photosystem I (PSI) containing one transmembrane helix. Ho-moplastomic transformants with an inactivatedpsaJgene were devoid of PSI-J protein. The mutant plants were slightly smaller and paler than wild-type because of a 13% reduction in chlorophyll content per leaf area caused by an 20% reduction in PSI. | ễFEBS Journal Knock-out of the chloroplast-encoded PSI-J subunit of photosystem I in Nicotiana tabacum PSI-J is required for efficient electron transfer and stable accumulation of photosystem I Andreas Hansson1 Katrin Amann2 Agnieszka Zygadlo1 Jorg Meurer2 Henrik V. Scheller1 and 1 Plant Biochemistry Laboratory Department of Plant Biology Faculty of Life Sciences University of Copenhagen Frederiksberg Denmark 2 Department Biologie I Botanik Ludwig-Maximilians-Universitat-Munchen Germany Keywords antenna size electron transport photosynthesis plastocyanin kinetics thylakoid membrane Correspondence P. E. Jensen Plant Biochemistry Laboratory Department of Plant Biology Faculty of Life Sciences University of Copenhagen 40 Thorvaldsensvej DK-1871 Frederiksberg C Denmark Fax 45 35 28 33 33 Tel 45 35 28 33 40 E-mail peje@ Received 30 August 2006 revised 21 December 2006 accepted 31 January 2007 doi The plastid-encoded psaJ gene encodes a hydrophobic low-molecular-mass subunit of photosystem I PSI containing one transmembrane helix. Ho-moplastomic transformants with an inactivated psaJ gene were devoid of PSI-J protein. The mutant plants were slightly smaller and paler than wildtype because of a 13 reduction in chlorophyll content per leaf area caused by an w 20 reduction in PSI. The amount of the peripheral antenna proteins Lhca2 and Lhca3 was decreased to the same level as the core subunits but Lhca1 and Lhca4 were present in relative excess. The functional size of the PSI antenna was not affected suggesting that PSI-J is not involved in binding of light-harvesting complex I. The specific PSI activity measured as NADP photoreduction in vitro revealed a 55 reduction in electron transport through PSI in the mutant. No significant difference in the second-order rate constant for electron transfer from reduced plastocyanin to oxidized P700 was observed in the absence of PSI-J. Instead a large fraction of PSI was found

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