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Life 2015, 5(2), 1172-1203; doi:10.3390/life5021172

Evolutionary Aspects and Regulation of Tetrapyrrole Biosynthesis in Cyanobacteria under Aerobic and Anaerobic Environments

Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya 464-8601, Japan
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Academic Editors: Robert Haselkorn and John C. Meeks
Received: 10 November 2014 / Revised: 23 March 2015 / Accepted: 24 March 2015 / Published: 30 March 2015
(This article belongs to the Special Issue Cyanobacteria: Ecology, Physiology and Genetics)
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Abstract

Chlorophyll a (Chl) is a light-absorbing tetrapyrrole pigment that is essential for photosynthesis. The molecule is produced from glutamate via a complex biosynthetic pathway comprised of at least 15 enzymatic steps. The first half of the Chl pathway is shared with heme biosynthesis, and the latter half, called the Mg-branch, is specific to Mg-containing Chl a. Bilin pigments, such as phycocyanobilin, are additionally produced from heme, so these light-harvesting pigments also share many common biosynthetic steps with Chl biosynthesis. Some of these common steps in the biosynthetic pathways of heme, Chl and bilins require molecular oxygen for catalysis, such as oxygen-dependent coproporphyrinogen III oxidase. Cyanobacteria thrive in diverse environments in terms of oxygen levels. To cope with Chl deficiency caused by low-oxygen conditions, cyanobacteria have developed elaborate mechanisms to maintain Chl production, even under microoxic environments. The use of enzymes specialized for low-oxygen conditions, such as oxygen-independent coproporphyrinogen III oxidase, constitutes part of a mechanism adapted to low-oxygen conditions. Another mechanism adaptive to hypoxic conditions is mediated by the transcriptional regulator ChlR that senses low oxygen and subsequently activates the transcription of genes encoding enzymes that work under low-oxygen tension. In diazotrophic cyanobacteria, this multilayered regulation also contributes in Chl biosynthesis by supporting energy production for nitrogen fixation that also requires low-oxygen conditions. We will also discuss the evolutionary implications of cyanobacterial tetrapyrrole biosynthesis and regulation, because low oxygen-type enzymes also appear to be evolutionarily older than oxygen-dependent enzymes. View Full-Text
Keywords: chlorophyll biosynthesis; analogous enzymes; hypoxia; transcriptional regulator; ChlR; nitrogen fixation chlorophyll biosynthesis; analogous enzymes; hypoxia; transcriptional regulator; ChlR; nitrogen fixation
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Fujita, Y.; Tsujimoto, R.; Aoki, R. Evolutionary Aspects and Regulation of Tetrapyrrole Biosynthesis in Cyanobacteria under Aerobic and Anaerobic Environments. Life 2015, 5, 1172-1203.

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