Chlorophyll alpha synthesis upon interruption and deletion of por coding for the light-dependent NADPH: protochlorophyllide oxidoreductase in a photosystem-I-less/chlL- strain of Synechocystis sp. PCC 6803.
The gene coding for the light-dependent NADPH:protochlorophyllide oxidoreductase (POR) was interrupted or deleted in a Synechocystis sp. PCC 6803 strain lacking photosystem I (PS I) as well as ChlL, which takes part in light-independent catalysis of protochlorophyllide reduction. Interruption of por by a kanamycin-resistance cartridge between the codons for M263 and V264 (about 83% into the coding region) did not abolish POR activity, but resulted in a decrease in the protochlorophyllide-(PChlide)-binding capacity of POR. Deletion of por in the PS I-less/chlL- strain generated a mutant [PS I-less/chlL-/por (del)] which accumulated both monovinyl-PChlide and divinyl-PChlide and excreted PChlides into the medium. This mutant also synthesized small amounts of protochlorophyllide dihydrogeranylgeraniol ester (protochlorophyll) when it was grown under light-activated heterotrophic growth conditions. However, the mutant was still able to synthesize small amounts of normal chlorophyll a under weak continuous illumination, even though the quantum yield of chlorophyll a formation was reduced. Either protochlorophyll or PChlide reduction by an unspecific reductase or by a ChlB/ChlN complex could account for chlorophyll a synthesis in the PS I-less/chlL-/por (del) strain. Functional photosystem II (PS II) was assembled in this mutant, but the PS II/chlorophyll ratio was fourfold lower than in the PS I-less strain with normal chlorophyll synthesis. The PS I-less/chlL-/por (del) mutant had a 77-K fluorescence emission maximum at 685 nm but no peak or shoulder at 695 nm when the cells were excited at 435 nm. Much of the chlorophyll in the PS I-less/chlL-/por (del) mutant therefore seems to be associated with components other than PS II.
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Department of Plant Biology, Arizona State University, Tempe 85287-1601, USA.
Brune
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Nieman
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Vermaas
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D002734:Chlorophyll / Q000096:biosynthesis* / Q000737:chemistry; D000077194:Chlorophyll A; D000458:Cyanobacteria / Q000235:genetics* / Q000378:metabolism* / Q000528:radiation effects; D017353:Gene Deletion; D005798:Genes, Bacterial; D008027:Light; D016254:Mutagenesis, Insertional; D010088:Oxidoreductases / Q000235:genetics* / Q000378:metabolism* / Q000528:radiation effects; D044925:Oxidoreductases Acting on CH-CH Group Donors; D045322:Photosynthetic Reaction Center Complex Proteins / Q000235:genetics / Q000378:metabolism; D011521:Protochlorophyllide / Q000737:chemistry / Q000378:metabolism
D045322:Photosynthetic Reaction Center Complex Proteins; D002734:Chlorophyll; D011521:Protochlorophyllide; D010088:Oxidoreductases; D044925:Oxidoreductases Acting on CH-CH Group Donors; C023886:protochlorophyllide reductase; D000077194:Chlorophyll A