Redox regulation of chlorophyll biosynthesis

• Published in: Phytochemistry (Oxford) 2010-06, Vol.71 (8), p.853-859
• Main Authors: Stenbaek, Anne, Jensen, Poul Erik
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; Chemical constitution; Chlorophyll - biosynthesis; Fundamental and applied biological sciences. Psychology; Light; Lyases - metabolism; Magnesium and ferro chelatase; Methyltransferases - metabolism; Mg-protoporphyrin IX methyltransferase; Mg-protoporphyrin monomethyl ester cyclase; Molecular Structure; NADPH-dependent thioredoxin reductase; Oxidation-Reduction; Plant physiology and development; Redox; Tetrapyrroles - metabolism; Thioredoxin-Disulfide Reductase - metabolism
• ISSN: 0031-9422; 1873-3700
• DOI: 10.1016/j.phytochem.2010.03.022

Chlorophyll captures and redirects light-energy and is essential for photosynthetic organisms. The Mg-chelatase which is situated at the branch point between the heme and the chlorophyll pathway fulfill a very important regulatory role and recent evidence suggests that the redox state of the chloroplast might be yet another regulator. A recently identified NADPH-dependent thioredoxin reductase (NTRC) might be involved in this redox regulation or, alternatively, protection of chlorophyll biosynthetic enzymes. Chlorophyll captures and redirects light-energy and is thus essential for photosynthetic organisms. The demand for chlorophyll differs throughout the day and night and in response to changing light conditions. Moreover, the chlorophyll biosynthesis pathway is up to certain points shared between the different tetrapyrroles; chlorophyll, heme, siroheme and phytochromobilin, for which the cell has different requirements at different time points. Combined with the phototoxic properties of tetrapyrroles which, if not properly protected, can lead to formation of reactive oxygen species (ROS), the need for a strict regulation of the chlorophyll biosynthetic pathway is obvious. Here we describe the current knowledge on regulation of chlorophyll biosynthesis in plants by the chloroplast redox state with emphasis on the Mg-chelatase situated at the branch point between the heme and the chlorophyll pathway. We discuss the proposed role of the Mg-chelatase as a key regulator of the tetrapyrrole pathway by its effect on enzymes both up- and downstream in the pathway and we specifically describe how redox state might regulate the Mg-branch. Finally, we propose that a recently identified NADPH-dependent thioredoxin reductase (NTRC) could be involved in redox regulation or protection of chlorophyll biosynthetic enzymes and describe the possible modes of action by this enzyme.