Inactivation of the geranylgeranyl reductase (ChlP) gene in the cyanobacterium Synechocystis sp. PCC 6803 |
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Authors: | Alexey V. Shpilyov Vladislav V. Zinchenko Bernhard Grimm |
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Affiliation: | a Department of Genetics, Biology Division, Moscow State University, Moscow, 119899, Russia b Institut für Biologie/Pflanzenphysiologie, Humboldt-Universität zu Berlin, Unter den Linden 6 (Sitz: Philippstr.13), D-10099 Berlin, Germany |
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Abstract: | Geranylgeranyl reductase catalyses the reduction of geranylgeranyl pyrophosphate to phytyl pyrophosphate required for synthesis of chlorophylls, phylloquinone and tocopherols. The gene chlP (ORF sll1091) encoding the enzyme has been inactivated in the cyanobacterium Synechocystis sp. PCC 6803. The resulting ΔchlP mutant accumulates exclusively geranylgeranylated chlorophyll a instead of its phytylated analogue as well as low amounts of α-tocotrienol instead of α-tocopherol. Whereas the contents of chlorophyll and total carotenoids are decreased, abundance of phycobilisomes is increased in ΔchlP cells. The mutant assembles functional photosystems I and II as judged from 77 K fluorescence and electron transport measurements. However, the mutant is unable to grow photoautotrophically due to instability and rapid degradation of the photosystems in the absence of added glucose. We suggest that instability of the photosystems in ΔchlP is directly related to accumulation of geranylgeranylated chlorophyll a. Increased rigidity of the chlorophyll isoprenoid tail moiety due to three additional CC bonds is the likely cause of photooxidative stress and reduced stability of photosynthetic pigment-protein complexes assembled with geranylgeranylated chlorophyll a in the ΔchlP mutant. |
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Keywords: | Chl a, (phytylated) chlorophyll a Chl agg, geranylgeranylated Chl a Chlide a, chlorophyllide a ChlG, chlorophyll synthase ChlP, geranylgeranyl reductase chlP, gene encoding ChlP DCBQ, 2,6-dichloro-p-benzoquinone GGPP, geranylgeranyl pyrophosphate Km/Kmr, kanamycin/kanamycin resistance OD, optical density ORF, open reading frame PBS, phycobilisome PC, phycocyanin PPP, phytyl pyrophosphate PSI, PSII, photosystem I, II RC, reaction center WT, wild type |
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