title: 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 light-harvesting 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.
authors.affiliation: Max-Planck-Institut für Molekulare Pflanzenphysiologie, D-14476 Potsdam-Golm, Germany.
authors.forename: Christin Anne
authors.initials: CA
authors.lastname: Albus
authors.forename: Annabel
authors.initials: A
authors.lastname: Salinas
authors.forename: Olaf
authors.initials: O
authors.lastname: Czarnecki
authors.forename: Sabine
authors.initials: S
authors.lastname: Kahlau
authors.forename: Maxi
authors.initials: M
authors.lastname: Rothbart
authors.forename: Wolfram
authors.initials: W
authors.lastname: Thiele
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Lein
authors.forename: Ralph
authors.initials: R
authors.lastname: Bock
authors.forename: Bernhard
authors.initials: B
authors.lastname: Grimm
authors.forename: Mark Aurel
authors.initials: MA
authors.lastname: Schöttler
mesh_terms: D000595:Amino Acid Sequence; D000622:Aminolevulinic Acid / Q000378:metabolism*; D002734:Chlorophyll / Q000378:metabolism; D000077194:Chlorophyll A; D017124:Conserved Sequence; D019143:Evolution, Molecular; D025461:Feedback, Physiological; D005453:Fluorescence; D018506:Gene Expression Regulation, Plant; D019746:Intramolecular Oxidoreductases / Q000737:chemistry / Q000378:metabolism*; D045342:Light-Harvesting Protein Complexes / Q000378:metabolism; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D010641:Phenotype; D010788:Photosynthesis / Q000235:genetics; D010940:Plant Proteins / Q000378:metabolism*; D018087:Plastids / Q000378:metabolism; D021381:Protein Transport; D011524:Protoporphyrins / Q000378:metabolism*; D016372:RNA, Antisense / Q000378:metabolism; D016415:Sequence Alignment; D045725:Tetrapyrroles / Q000378:metabolism; D014026:Nicotiana / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development
chemical_list: D045342:Light-Harvesting Protein Complexes; D010940:Plant Proteins; D011524:Protoporphyrins; D016372:RNA, Antisense; D045725:Tetrapyrroles; D002734:Chlorophyll; C039629:magnesium protoporphyrin; D000622:Aminolevulinic Acid; D019746:Intramolecular Oxidoreductases; D000077194:Chlorophyll A