slr1923 of Synechocystis sp. PCC6803 Is Essential for Conversion of 3,8-Divinyl(proto)chlorophyll(ide) to 3-Monovinyl(proto)chlorophyll(ide)

Abstract

The deduced amino acid sequence of an slr1923 gene of Synechocystis sp. PCC6803 is homologous to archaean F 420 H 2 dehydrogenase, which acts as a soluble subcomplex of reduced nicotinamide adenine dinucleotide dehydrogenase complex I. In this study, the gene was inactivated and characteristics of the mutant were analyzed. The mutant grew slower than the wild type under 100 mE m 22 s 21 but did not grow under high light intensity (300 mE m 22 s 21 ). The cellular content of chlorophyll was lower in the mutant, and the absorption spectrum showed a shift in the absorption peak of the Soret band to a longer wavelength by about 10 nm compared with the wild type. It was found, by high-performance liquid chromatography analysis, that the retention time of chlorophyll of the mutant is shorter than that of the wild type and that the peak wavelength of the Soret band was also shifted to a longer wavelength by 11 nm. Proton nuclear magnetic resonance analysis of the chlorophyll of the mutant revealed that the ethyl group of position 8 of ring B is replaced with a vinyl group. The spectrum indicates that the chlorophyll of the mutant is not a normal (3-vinyl)chlorophyll a but a 3,8-divinylchlorophyll a. These results strongly suggest that the Slr1923 protein is essential for the conversion from divinylchlorophyll(ide) to normal chlorophyll(ide). We thus designate this gene cvrA (a gene indispensable for cyanobacterial vinyl reductase).Land plants, algae, cyanobacteria, and photosynthetic bacteria use various types of chlorophyll molecules (chlorophyll [chl] a, b, c, and d and bacteriochlorophyll a, b, c, etc.) as inevitable photon-capturing pigments in photosynthesis. Extensive studies with various organisms by biochemical and genetic approaches have disclosed many aspects related to chlorophyll metabolism (for review, see Beale, 1993Beale, , 1999Senge and Smith, 1995). However, the functional or regulatory genes related to various chlorophyll biosynthetic pathways have not yet been fully elucidated. In land plants, chlorophyll precursors are sometimes accumulated as both 3-monovinyl (MV-) or 3,8-divinyl (DV-) intermediates, and the ratio between the two forms changes depending on the species, tissues, and growth conditions (Kim and Rebeiz, 1996). Chlorophyll biosynthetic heterogeneity is assumed to originate mainly in parallel DV-and MV-chl biosynthetic routes interconnected by 8-vinyl reductases (8 VRs) that convert DV-tetrapyrroles to MV-tetrapyrroles by conversion of the vinyl group at position 8 of ring B to the ethyl group. So far, five 8-VR activities have been detected at the levels of DV-Mg-protophorphyrin IX, Mg-protomonomethyl ester, protochlorophyllide (Pchlide) a, chlorophyllide (chlide) a, and chl a (Kolossov et al.,

One Divinyl Reductase Reduces the 8-Vinyl Groups in Various Intermediates of Chlorophyll Biosynthesis in a Given Higher Plant Species, But the Isozyme Differs between Species

“…A maize mutant accumulated only DV-Chls (Bazzaz, 1981;, which implied that a single gene product might be responsible for the reduction of the 8-vinyl group of Chl intermediates, although the possibility that the gene encodes a regulator for the divinyl reduction could not be excluded. The AtDVR (AT5G18660)-inactivated pcb2 mutant of Arabidopsis also exclusively accumulated DV-Chls in 16-d-old whole plants, which suggested that Arabidopsis could contain only one functional DVR (Beale, 2005;Nakanishi et al, 2005), but other possibilities were also proposed (Islam et al, 2008;Ito et al, 2008). Previously, we reported that the OsDVR (Os03g22780)-inactivated 824ys mutant of rice accumulated only DV-Chls and no MVChls in leaf blade of 4-week-old plants (Wang et al, 2010).…”

“…Collectively, we are confident that a single DVR protein is responsible for reducing the 8-vinyl groups of various intermediate molecules of Chl biosynthesis in higher plants, at least in angiosperms represented by rice and Arabidopsis. Nonetheless, two DVRs, BciA (CT1063) and BciB (CvrA, Slr1923), have been identified in photosynthetic bacteria and are sufficient to independently produce 8-vinyl reductase activity (Chew and Bryant, 2007;Islam et al, 2008;Ito et al, 2008;Liu and Bryant, 2011). Multiple amino acid sequence alignment indicated that BciA is a homolog of both OsDVR (Os03g22780) and AtDVR (At5G18660), whereas BciB has no homology to both OsDVR and AtDVR.…”

“…However, at that time, we examined Chl compositions of the mutant only using leaf blades of 4-week-old plants (at the five-leaf stage). We could not exclude the possible accumulation of MV-Chls generated by DVRs other than OsDVR in the mutant if we did not check various tissues during various developmental stages (Islam et al, 2008;Ito et al, 2008). To this end, we systematically investigated Chl compositions in leaf blade, leaf sheath, uppermost internode, panicle rachis, glume, and caryopsis of the 824ys mutant at seedling, tillering, flowering, filling, and maturation stages.…”

Chlorophyllide a Oxidoreductase Works as One of the Divinyl Reductases Specifically Involved in Bacteriochlorophyll a Biosynthesis

“…By contrast, in genomes of many cyanobacteria, no orthologs of plant-type DVR and BciA were found, but a nonhomologous slr1923 gene in the cyanobacterium Synechocystis sp. PCC6803 did code an enzyme showing DVR activity (16,17), which is here called cyano-type DVR. Many orthologs of cyano-type DVR were also found in genomes of anoxygenic photosynthetic bacteria.…”

Multiple Types of 8-Vinyl Reductases for (Bacterio)Chlorophyll Biosynthesis Occur in Many Green Sulfur Bacteria

“…In the cyanobacterium Synechococystis sp. strain PCC 6803, ORF slr1923 encodes a product essential for C-8 vinyl reduction (9,10). Homologs of slr1923 are found in most but not all chlorophototrophic organisms without bciA homologs (10).…”