spotlight on protochlorophyllide reduction.

Chlorophylls (Chls) play pivotal roles in energy absorption and transduction and also in charge separation in reaction centers in all photosynthetic organisms. In Chl biosynthesis steps, only a step for the enzymatic reduction of protochlorophyllide (Pchlide) to chlorophyllide (Chlide) is mediated by both nuclear- and chloroplast-encoded genes in land plants. Many plants encode the genes for light-dependent Pchlide reductase (LPOR) and light-independent Pchlide reductase (DPOR) in the nucleus and chloroplast genome, respectively. During the diversification of land plants, the reduction step of Pchlide to Chlide has become solely dependent on LPOR, and the genes for DPOR have been lost from chloroplast genome. It remains unclear why DPOR persists in some land plants, how they were eliminated from chloroplast genomes during the diversification of land plants, and under what environmental conditions DPOR was required. We demonstrate that DPOR is functional in liverwort (Marchantia polymorpha L.) and plays an important role in Chl biosynthesis. Having established a plastid transformation system in liverwort, we disrupted chlB, which encodes a subunit of DPOR in the M. polymorpha chloroplast genome. Morphological and Chl content analysis of a chlB mutant grown under different photoperiods revealed that DPOR is particularly required for Chl biosynthesis under short-day conditions. Our findings suggest that an environmental condition in the form of photoperiod is an important factor that determines the loss or retention of chloroplast-encoded genes mediating Pchlide reduction to Chlide.

Inhibition of chlorophyll biosynthesis at the ..

Chlorophyll Biosynthesis in Bacteria: The Origins of Structural and Functional Diversity

Spotlight on Protochlorophyllide Reduction.

Photosynthesis converts solar energy to chemical energy using chlorophylls (Chls). In a late stage of biosynthesis of Chls, dark-operative protochlorophyllide (Pchlide) oxidoreductase (DPOR), a nitrogenase-like enzyme, reduces the C17 = C18 double bond of Pchlide and drastically changes the spectral properties suitable for photosynthesis forming the parental chlorin ring for Chl a. We previously proposed that the spatial arrangement of the proton donors determines the stereospecificity of the Pchlide reduction based on the recently resolved structure of the DPOR catalytic component, NB-protein. However, it was not clear how the two-electron and two-proton transfer events are coordinated in the reaction. In this study, we demonstrate that DPOR initiates a single electron transfer reaction from a [4Fe-4S]-cluster (NB-cluster) to Pchlide, generating Pchlide anion radicals followed by a single proton transfer, and then, further electron/proton transfer steps transform the anion radicals into chlorophyllide (Chlide). Thus, DPOR is a unique iron-sulphur enzyme to form substrate radicals followed by sequential proton- and electron-transfer steps with the protein folding very similar to that of nitrogenase. This novel radical-mediated reaction supports the biosynthesis of Chl in a wide variety of photosynthetic organisms.

13 Chlorophylls and Bilins: Biosynthesis, ..

DPOR has been lost and the reduction step of Pchlide to Chlide has become solely dependent on LPOR in angiosperms, several gymnosperms, and some Pteridophytes (). Based on LPOR and DPOR distribution in the plant, eubacterial, and archaebacterial kingdoms and the oxygen sensitivity of DPOR, a model has been proposed to explain the gene transfer of LPOR and the substitution of LPOR for DPOR during land plant evolution: 1) oxygen-sensitive DPOR initially emerged when the atmosphere of Archaean Earth was anaerobic, presumably from nitrogenase-like genes () and 2) LPOR, which is an oxygen-insensitive and light- and NADPH-dependent enzyme belonging to a short-chain dehydrogenase/reductase superfamily, evolved during the transition from an anaerobic to aerobic atmosphere (, ). Both enzymes seem to have emerged before the endosymbiosis of cyanobacteria, which are believed to be the ancestors of chloroplasts, given that Chlides are biosynthesized using both DPOR and LPOR in modern cyanobacteria (). 3) Upon the establishment of chloroplasts, it is likely that LPOR was transferred to the nucleus, whereas the genes for DPOR were retained in chloroplast genomes. Despite their apparent functional redundancy, both genes have been strictly retained in several algae, lower plants, and gymnosperms. 4) As a final step of “gene replacement,” DPOR loss independently occurred in land plants.

Number of amino acids: 397
Tanaka R and Tanaka A (2007) Tetrapyrrole biosynthesis in higher plants. Annual Review of Plant Biology 58: 321–346.

coordinated with chlorophyll biosynthesis during the ..

A crucial regulatory step in the biosynthesis of chlorophyll in higher plants and algae is the reduction of protochlorophyllide to chlorophyllide. POR is unique in its formation as it directly utilizes light for catalysis. POR is a major protein in the membrane of plants, without it, the chloroplasts would remain inactive. The protochlorophyllide absorbs light, excites the molecule and is reduced by NADPH to form chlorophyllide. The illumination of POR and its conversion of protochlorophyllide to chlorophyllide transforms etiolated membranes to active chloroplasts, which in turn provides energy to the plant once chlorophyll is produced. The absorption of light by the co-enzyme complex developed from the interaction of POR and NADPH induces hydrogen transfer resulting in the formation of chlorophyllide and NADP+ .

Reinbothe, C., et al. (2010).

Chlorophyll biosynthesis: spotlight on ..

Akhtar M (2003) Coproporphyrinogen III and protoporphyrinogen IX oxidases. In: Kadish KM, Smith KM and Guilard R, (eds). The Porphyrin Handbook. Vol. 12 Iron and Cobalt Pigments: Biosynthesis, Structure, and Degradation, pp. 75–92. New York: Elsevier Science.

Jan 06, 1999 · Chlorophyll biosynthesis: spotlight on protochlorophyllide reduction

chlB Requirement for Chlorophyll Biosynthesis under …

Chlorophylls are complexed with their binding proteins and serve two primary functions in photosynthesis: they trap light energy and transfer it to the reaction centers of photosystems , . During light absorption and energy transfer, chlorophylls inevitably generate highly reactive singlet oxygen, particularly under strong light, leading to the inhibition of photosynthesis, plant growth and even to cell death , . In addition, many chlorophyll precursors present in their free state are strong photosensitizers that produce reactive oxygen species upon light illumination. Therefore, the chlorophyll biosynthetic pathway is strictly regulated in response to developmental and environmental cues.