Abstract
The flavodiiron proteins (FDPs) are involved in the detoxification of oxidative compounds, such as nitric oxide (NO) or O2 in Archaea and Bacteria. In cyanobacteria, the FDPs Flv1 and Flv3 are essential in the light-dependent reduction of O2 downstream of PSI. Phylogenetic analysis revealed that two genes (flvA and flvB) in the genome of Chlamydomonas reinhardtii show high homology to flv1 and flv3 genes of the cyanobacterium Synechocystis sp. PCC 6803. The physiological role of these FDPs in eukaryotic green algae is not known, but it is of a special interest since these phototrophic organisms perform oxygenic photosynthesis similar to higher plants, which do not possess FDP homologs. We have analyzed the levels of flvA and flvB transcripts in C. reinhardtii cells under various environmental conditions and showed that these genes are highly expressed under ambient CO2 levels and during the early phase of acclimation to sulfur deprivation, just before the onset of anaerobiosis and the induction of efficient H2 photoproduction. Importantly, the increase in transcript levels of the flvA and flvB genes was also corroborated by protein levels. These results strongly suggest the involvement of FLVA and FLVB proteins in alternative electron transport.
Highlights
Chlamydomonas reinhardtii is a soil-dwelling green alga with great flexibility in its photosynthetic machinery and metabolism, which are employed to cope with changing light, carbon and nutrient supplies and oxic/anoxic conditions
As a first approach to obtain information about the function of flavodiiron protein (FDP) in C. reinhardtii, we applied real-time quantitative reverse transcription–PCR (RT–qPCR) to determine the response of flv transcript levels to varying environmental conditions
The determination of appropriate reference genes for each organism under particular environmental conditions is crucial to employing the correct normalization strategy to transcript analysis (Huggett et al 2005, Guenin et al 2009)
Summary
Chlamydomonas reinhardtii is a soil-dwelling green alga with great flexibility in its photosynthetic machinery and metabolism, which are employed to cope with changing light, carbon and nutrient supplies and oxic/anoxic conditions. During photosynthesis, specialized antenna complexes harvest and transfer light energy to the PSII and PSI reaction centers, where primary charge separation initiates photosynthetic linear electron flow by oxidizing water at PSII and reducing NADP+ to NADPH downstream of PSI. These electron transfer reactions are coupled with proton pumping across the thylakoid membrane, and the resulting proton gradient, ÁpH, drives the ATP synthesis. Strain PCC 6803 (hereafter, Synechocystis) flv genes, it is highly conceivable that the proteins encoded by these genes are involved in photosynthetic electron transport in C. reinhardtii Since C. reinhardtii possesses two genes with high homology to Synechocystis sp. strain PCC 6803 (hereafter, Synechocystis) flv genes, it is highly conceivable that the proteins encoded by these genes are involved in photosynthetic electron transport in C. reinhardtii
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