A novel ”oxygen-induced” greening process in a cyanobacterial mutant lacking the transcriptional activator ChlR involved in low-oxygen adaptation of tetrapyrrole biosynthesis [Plant Biology]

December 2nd, 2013 by Aoki, R., Hiraide, Y., Yamakawa, H., Fujita, Y.

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, ∆chlR, 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 ∆chlR cells in low-oxygen conditions and the subsequent re-greening of the etiolated cells upon exposure to oxygen, by HPLC, Western blotting and low-temperature fluorescence spectra. The Chl content of the etiolated ∆chlR 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 Mg-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 ∆chlR cells resumed to produce Chl after a short lag (about 2 hours) and the level at 72 hours 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 hours, the PSI content reached about 50% of the wild-type level in contrast to the full recovery of PSII. ∆chlR provides a promising alternative system to investigate the biogenesis of PSI and PSII.
  • Posted in Journal of Biological Chemistry, Publications
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