title: A novel "oxygen-induced" greening process in a cyanobacterial mutant lacking the transcriptional activator ChlR involved in low-oxygen adaptation of tetrapyrrole biosynthesis.
abstract: ChlR activates the transcription of the chlAII-ho2-hemN operon in response to low-oxygen conditions in the cyanobacterium Synechocystis sp. PCC 6803. Three genes in the operon encode low-oxygen-type enzymes to bypass three oxygen-dependent reactions in tetrapyrrole biosynthesis. A chlR-lacking mutant, ΔchlR, shows poor photoautotrophic growth due to low chlorophyll (Chl) content under low-oxygen conditions, which is caused by no induction of the operon. Here, we characterized the processes of etiolation of ΔchlR cells in low-oxygen conditions and the subsequent regreening of the etiolated cells upon exposure to oxygen, by HPLC, Western blotting, and low-temperature fluorescence spectra. The Chl content of the etiolated ΔchlR cells incubated under low-oxygen conditions for 7 days was only 10% of that of the wild-type with accumulation of almost all intermediates of the magnesium branch of Chl biosynthesis. Both photosystem I (PSI) and photosystem II (PSII) were significantly decreased, accompanied by a preferential decrease of antenna Chl in PSI. Upon exposure to oxygen, the etiolated ΔchlR cells resumed to produce Chl after a short lag (∼2 h), and the level at 72 h was 80% of that of the wild-type. During this novel "oxygen-induced" greening process, the PSI and PSII contents were largely increased in parallel with the increase in Chl contents. After 72 h, the PSI content reached ∼50% of the wild-type level in contrast to the full recovery of PSII. ΔchlR provides a promising alternative system to investigate the biogenesis of PSI and PSII.
authors.affiliation: From the Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya 464-8601, Japan.
authors.forename: Rina
authors.initials: R
authors.lastname: Aoki
authors.forename: Yuto
authors.initials: Y
authors.lastname: Hiraide
authors.forename: Hisanori
authors.initials: H
authors.lastname: Yamakawa
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Fujita
mesh_terms: D000222:Adaptation, Physiological; D001426:Bacterial Proteins; D002734:Chlorophyll / Q000096:biosynthesis* / Q000235:genetics; D009154:Mutation; D010100:Oxygen / Q000378:metabolism*; D045331:Photosystem I Protein Complex / Q000096:biosynthesis / Q000235:genetics; D045332:Photosystem II Protein Complex / Q000096:biosynthesis / Q000235:genetics; D046939:Synechocystis / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors
chemical_list: D001426:Bacterial Proteins; D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D014157:Transcription Factors; D002734:Chlorophyll; D010100:Oxygen
keywords: Chlorophyll; Cyanobacteria; Greening; Hypoxia; Photosynthesis; Photosynthetic Pigments; Photosystem II; Transcriptional Regulator