title: The 2-C-methylerythritol 4-phosphate pathway in melon is regulated by specialized isoforms for the first and last steps.
abstract: The 2-C-methyl-d-erythritol-4-phosphate (MEP) pathway provides the precursors for the biosynthesis of plastidial isoprenoids, which include the carotenoid pigments of many fruits. We have analysed the genes encoding the seven enzymes of the MEP pathway in melon (Cucumis melo L.) and determined that the first one, 1-deoxyxylulose 5-phosphate synthase (DXS), and the last one, 1-hydroxy-2-methyl-2-(E)-butenyl 4-diphosphate reductase (HDR), are represented in the genome as a small gene family and paralogous pair, respectively. In the case of DXS, three genes encode functional DXS activities which fall into previously established type I (CmDXS1) and II (CmDXS2a and CmDXS2b) categories, while a fourth DXS-like gene belonging to the type III group did not encode a protein with DXS activity. Their expression patterns and phylogenies suggest that CmDXS1 is functionally specialized for developmental and photosynthetic processes, while CmDXS2a and CmDXS2b are induced in flowers and ripening fruit of orange- (but not white-) fleshed varieties, coinciding with β-carotene accumulation. This is the first instance connecting type II DXS genes to specialized isoprenoid biosynthesis in the fruit of an agronomically important species. Two HDR paralogues were shown to encode functional enzymes, although only CmHDR1 was highly expressed in the tissues and developmental stages tested. Phylogenetic analysis showed that in cucurbits such as melon, these HDR paralogues probably arose through individual gene duplications in a common angiosperm ancestor, mimicking a prior division in gymnosperms, while other flowering plants, including apple, soy, canola, and poplar, acquired HDR duplicates recently as homoeologues through large-scale genome duplications. We report the influence of gene duplication history on the regulation of the MEP pathway in melon and the role of specialized MEP-pathway isoforms in providing precursors for β-carotene production in orange-fleshed melon varieties.
authors.affiliation: Plant and Animal Genomics Programme, Institut de Recerca i Tecnologia Agroalimentàries and Centre for Research in Agricultural Genomics, CSIC-IRTA-UAB-UB, 08193 Barcelona, Spain.
authors.forename: Montserrat
authors.initials: M
authors.lastname: Saladié
authors.affiliation: Department of Biochemistry, Max Planck Institute for Chemical Ecology, Beutenberg Campus, Hans Knöll Street 8, 07745 Jena, Germany.
authors.forename: Louwrance P
authors.initials: LP
authors.lastname: Wright
authors.affiliation: Plant and Animal Genomics Programme, Institut de Recerca i Tecnologia Agroalimentàries and Centre for Research in Agricultural Genomics, CSIC-IRTA-UAB-UB, 08193 Barcelona, Spain.
authors.forename: Jordi
authors.initials: J
authors.lastname: Garcia-Mas
authors.affiliation: Plant Metabolism and Metabolic Engineering Programme, Centre for Research in Agricultural Genomics, CSIC-IRTA-UAB-UB, 08193 Barcelona, Spain.
authors.forename: Manuel
authors.initials: M
authors.lastname: Rodriguez-Concepcion
authors.affiliation: Plant Metabolism and Metabolic Engineering Programme, Centre for Research in Agricultural Genomics, CSIC-IRTA-UAB-UB, 08193 Barcelona, Spain michael.phillips@cragenomica.es.
authors.forename: Michael A
authors.initials: MA
authors.lastname: Phillips
mesh_terms: D000595:Amino Acid Sequence; D002338:Carotenoids / Q000096:biosynthesis*; D002851:Chromatography, High Pressure Liquid; D028463:Cucumis melo / Q000201:enzymology / Q000235:genetics* / Q000378:metabolism; D004896:Erythritol / Q000031:analogs & derivatives* / Q000378:metabolism; D020440:Gene Duplication; D018506:Gene Expression Regulation, Plant; D008969:Molecular Sequence Data; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism; D010802:Phylogeny; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D060888:Real-Time Polymerase Chain Reaction; D016415:Sequence Alignment; D013403:Sugar Phosphates / Q000378:metabolism*; D014166:Transferases / Q000235:genetics / Q000378:metabolism
chemical_list: C114232:2-C-methylerythritol 4-phosphate; D010940:Plant Proteins; D020033:Protein Isoforms; D013403:Sugar Phosphates; D002338:Carotenoids; D010088:Oxidoreductases; D014166:Transferases; C109461:deoxyxylulose-5-phosphate synthase; D004896:Erythritol
keywords: 2-C-methylerythritol 4-phosphate; carotenoids; fruit development; isoprenoid biosynthesis; melon; metabolite profiling; phylogenetics; transcript profiling.