LCAA, a Novel Factor Required for Magnesium Protoporphyrin Monomethylester Cyclase Accumulation and Feedback Control of Aminolevulinic Acid Biosynthesis in Tobacco    

Abstract

Low Chlorophyll Accumulation A (LCAA) antisense plants were obtained from a screen for genes whose partial down-regulation results in a strong chlorophyll deficiency in tobacco (Nicotiana tabacum). The LCAA mutants are affected in a plastid-localized protein of unknown function, which is conserved in cyanobacteria and all photosynthetic eukaryotes. They suffer from drastically reduced lightharvesting complex (LHC) contents, while the accumulation of all other photosynthetic complexes per leaf area is less affected. As the disturbed accumulation of LHC proteins could be either attributable to a defect in LHC biogenesis itself or to a bottleneck in chlorophyll biosynthesis, chlorophyll synthesis rates and chlorophyll synthesis intermediates were measured. LCAA antisense plants accumulate magnesium (Mg) protoporphyrin monomethylester and contain reduced protochlorophyllide levels and a reduced content of CHL27, a subunit of the Mg protoporphyrin monomethylester cyclase. Bimolecular fluorescence complementation assays confirm a direct interaction between LCAA and CHL27. 5-Aminolevulinic acid synthesis rates are increased and correlate with an increased content of glutamyl-transfer RNA reductase. We suggest that LCAA encodes an additional subunit of the Mg protoporphyrin monomethylester cyclase, is required for the stability of CHL27, and contributes to feedback-control of 5-aminolevulinic acid biosynthesis, the rate-limiting step of chlorophyll biosynthesis.Photosynthetic electron transport, CO 2 fixation by the Calvin cycle, and sulfur and nitrogen assimilation all occur within the chloroplasts of photosynthetic eukaryotes, which also harbor several anabolic pathways utilizing the primary photoassimilates, such as amino acid, nucleotide, isoprenoid, and lipid synthesis. Also, the biosynthesis of several important cellular key metabolites, such as chromophores and cofactors required for photosynthesis and respiration, is localized in

Inducible Repression of Nuclear-Encoded Subunits of the Cytochrome b6f Complex in Tobacco Reveals an Extraordinarily Long Lifetime of the Complex

“…Primers for the real-time reverse transcription-PCR analysis were designed as described by Albus et al (2012). The melting temperature was set to 60°C, the amplicon length was set between 50 and 180 bp, and the guanine-cytosin content of the amplicon varied between 35% and 65% (Supplemental Table S1).…”

LIL3, a Light-Harvesting Complex Protein, Links Terpenoid and Tetrapyrrole Biosynthesis in Arabidopsis thaliana

“…The stability of macromolecular protein assemblies is facilitated through direct physical interactions among the proteins. This interplay is often supported by nonenzymatic chaperones and auxiliary factors (Tanaka et al, 2010;Albus et al, 2012;Mork-Jansson et al, 2015a).…”

Three classes of oxygen-dependent cyclase involved in chlorophyll and bacteriochlorophyll biosynthesis

“…A mutant depleted in Ycf54 had a significantly reduced Chl content, accumulated MgPME, was only able to tolerate low light intensities and was unable to grow under photoautotrophic conditions (21,22). Antisense mutants of the ortholog of ycf54 in tobacco, LCAA, also demonstrated impaired cyclase activity, and the dimeric protein was shown to interact with CHL27 in the chloroplast (23). The foregoing findings suggest that Ycf54/LCAA, conserved among oxygenic phototrophs, is the "missing" soluble Significance (Bacterio)chlorophylls harvest and convert the solar energy that powers the biosphere.…”