title: Extending the biosynthetic repertoires of cyanobacteria and chloroplasts.
abstract: Chloroplasts in plants and algae and photosynthetic microorganisms such as cyanobacteria are emerging hosts for sustainable production of valuable biochemicals, using only inorganic nutrients, water, CO2 and light as inputs. In the past decade, many bioengineering efforts have focused on metabolic engineering and synthetic biology in the chloroplast or in cyanobacteria for the production of fuels, chemicals and complex, high-value bioactive molecules. Biosynthesis of all these compounds can be performed in photosynthetic organelles/organisms by heterologous expression of the appropriate pathways, but this requires optimization of carbon flux and reducing power, and a thorough understanding of regulatory pathways. Secretion or storage of the compounds produced can be exploited for the isolation or confinement of the desired compounds. In this review, we explore the use of chloroplasts and cyanobacteria as biosynthetic compartments and hosts, and we estimate the levels of production to be expected from photosynthetic hosts in light of the fraction of electrons and carbon that can potentially be diverted from photosynthesis. The supply of reducing power, in the form of electrons derived from the photosynthetic light reactions, appears to be non-limiting, but redirection of the fixed carbon via precursor molecules presents a challenge. We also discuss the available synthetic biology tools and the need to expand the molecular toolbox to facilitate cellular reprogramming for increased production yields in both cyanobacteria and chloroplasts.
authors.affiliation: Copenhagen Plant Science Center, VILLUM Research Center for Plant Plasticity, Center for Synthetic Biology 'bioSYNergy', Department of Plant and Environmental Sciences, University of Copenhagen, Thorvaldsensvej 40, DK-1871, Frederiksberg C, Denmark.
authors.forename: Agnieszka Zygadlo
authors.initials: AZ
authors.lastname: Nielsen
authors.affiliation: Copenhagen Plant Science Center, VILLUM Research Center for Plant Plasticity, Center for Synthetic Biology 'bioSYNergy', Department of Plant and Environmental Sciences, University of Copenhagen, Thorvaldsensvej 40, DK-1871, Frederiksberg C, Denmark.
authors.forename: Silas Busck
authors.initials: SB
authors.lastname: Mellor
authors.affiliation: Copenhagen Plant Science Center, VILLUM Research Center for Plant Plasticity, Center for Synthetic Biology 'bioSYNergy', Department of Plant and Environmental Sciences, University of Copenhagen, Thorvaldsensvej 40, DK-1871, Frederiksberg C, Denmark.
authors.forename: Konstantinos
authors.initials: K
authors.lastname: Vavitsas
authors.affiliation: Copenhagen Plant Science Center, VILLUM Research Center for Plant Plasticity, Center for Synthetic Biology 'bioSYNergy', Department of Plant and Environmental Sciences, University of Copenhagen, Thorvaldsensvej 40, DK-1871, Frederiksberg C, Denmark.
authors.forename: Artur Jacek
authors.initials: AJ
authors.lastname: Wlodarczyk
authors.affiliation: Copenhagen Plant Science Center, VILLUM Research Center for Plant Plasticity, Center for Synthetic Biology 'bioSYNergy', Department of Plant and Environmental Sciences, University of Copenhagen, Thorvaldsensvej 40, DK-1871, Frederiksberg C, Denmark.
authors.forename: Thiyagarajan
authors.initials: T
authors.lastname: Gnanasekaran
authors.affiliation: Copenhagen Plant Science Center, VILLUM Research Center for Plant Plasticity, Center for Synthetic Biology 'bioSYNergy', Department of Plant and Environmental Sciences, University of Copenhagen, Thorvaldsensvej 40, DK-1871, Frederiksberg C, Denmark.
authors.forename: Maria
authors.initials: M
authors.lastname: Perestrello Ramos H de Jesus
authors.affiliation: Copenhagen Plant Science Center, VILLUM Research Center for Plant Plasticity, Center for Synthetic Biology 'bioSYNergy', Department of Plant and Environmental Sciences, University of Copenhagen, Thorvaldsensvej 40, DK-1871, Frederiksberg C, Denmark.
authors.forename: Brian Christopher
authors.initials: BC
authors.lastname: King
authors.affiliation: Copenhagen Plant Science Center, VILLUM Research Center for Plant Plasticity, Center for Synthetic Biology 'bioSYNergy', Department of Plant and Environmental Sciences, University of Copenhagen, Thorvaldsensvej 40, DK-1871, Frederiksberg C, Denmark.
authors.forename: Kamil
authors.initials: K
authors.lastname: Bakowski
authors.affiliation: Copenhagen Plant Science Center, VILLUM Research Center for Plant Plasticity, Center for Synthetic Biology 'bioSYNergy', Department of Plant and Environmental Sciences, University of Copenhagen, Thorvaldsensvej 40, DK-1871, Frederiksberg C, Denmark.
authors.forename: Poul Erik
authors.initials: PE
authors.lastname: Jensen
mesh_terms: D002244:Carbon / Q000378:metabolism; D002245:Carbon Dioxide / Q000378:metabolism; D002736:Chloroplasts / Q000378:metabolism*; D000458:Cyanobacteria / Q000378:metabolism* / Q000502:physiology; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D004224:Diterpenes / Q000378:metabolism; D060847:Metabolic Engineering / Q000379:methods; D010788:Photosynthesis / Q000502:physiology; D058615:Synthetic Biology / Q000379:methods
chemical_list: D004224:Diterpenes; D002245:Carbon Dioxide; D002244:Carbon; D003577:Cytochrome P-450 Enzyme System
keywords: carbon assimilation; cytochromes P450; diterpenoids; metabolites; photosynthetic efficiency; synthetic biology toolbox