title: Systems biology and metabolic modelling unveils limitations to polyhydroxybutyrate accumulation in sugarcane leaves; lessons for C4 engineering.
abstract: In planta production of the bioplastic polyhydroxybutyrate (PHB) is one important way in which plant biotechnology can address environmental problems and emerging issues related to peak oil. However, high biomass C4 plants such as maize, switch grass and sugarcane develop adverse phenotypes including stunting, chlorosis and reduced biomass as PHB levels in leaves increase. In this study, we explore limitations to PHB accumulation in sugarcane chloroplasts using a systems biology approach, coupled with a metabolic model of C4 photosynthesis. Decreased assimilation was evident in high PHB-producing sugarcane plants, which also showed a dramatic decrease in sucrose and starch content of leaves. A subtle decrease in the C/N ratio was found which was not associated with a decrease in total protein content. An increase in amino acids used for nitrogen recapture was also observed. Based on the accumulation of substrates of ATP-dependent reactions, we hypothesized ATP starvation in bundle sheath chloroplasts. This was supported by mRNA differential expression patterns. The disruption in ATP supply in bundle sheath cells appears to be linked to the physical presence of the PHB polymer which may disrupt photosynthesis by scattering photosynthetically active radiation and/or physically disrupting thylakoid membranes.
authors.affiliation: Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, Brisbane, Qld, Australia.
authors.forename: Richard B
authors.identifier: http://orcid.org/0000-0002-1341-7871
authors.initials: RB
authors.lastname: McQualter
authors.affiliation: Department of Animal and Plant Sciences, University of Sheffield, Western Bank, Sheffield, UK.
authors.forename: Chandra
authors.initials: C
authors.lastname: Bellasio
authors.affiliation: Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, Brisbane, Qld, Australia.
authors.forename: Leigh K
authors.initials: LK
authors.lastname: Gebbie
authors.affiliation: Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, Brisbane, Qld, Australia.
authors.forename: Lars A
authors.initials: LA
authors.lastname: Petrasovits
authors.affiliation: Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, Brisbane, Qld, Australia.
authors.forename: Robin W
authors.initials: RW
authors.lastname: Palfreyman
authors.affiliation: Metabolomics Australia Queensland Node, Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, Brisbane, Qld, Australia.
authors.forename: Mark P
authors.initials: MP
authors.lastname: Hodson
authors.affiliation: Metabolomics Australia Queensland Node, Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, Brisbane, Qld, Australia.
authors.forename: Manuel R
authors.initials: MR
authors.lastname: Plan
authors.affiliation: Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, Brisbane, Qld, Australia.
authors.forename: Deborah M
authors.initials: DM
authors.lastname: Blackman
authors.affiliation: Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, Brisbane, Qld, Australia.
authors.forename: Stevens M
authors.initials: SM
authors.lastname: Brumbley
authors.affiliation: Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, Brisbane, Qld, Australia.
authors.forename: Lars K
authors.initials: LK
authors.lastname: Nielsen
mesh_terms: D002244:Carbon / Q000378:metabolism*; D002736:Chloroplasts / Q000378:metabolism / Q000648:ultrastructure; D002940:Circadian Rhythm; D018506:Gene Expression Regulation, Plant; D006885:Hydroxybutyrates / Q000378:metabolism; D060847:Metabolic Engineering / Q000379:methods*; D055442:Metabolome; D008954:Models, Biological; D009584:Nitrogen / Q000378:metabolism; D010788:Photosynthesis; D018515:Plant Leaves / Q000378:metabolism*; D030821:Plants, Genetically Modified; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D031786:Saccharum / Q000235:genetics / Q000378:metabolism*; D049490:Systems Biology / Q000379:methods*
chemical_list: D006885:Hydroxybutyrates; D012333:RNA, Messenger; D002244:Carbon; D009584:Nitrogen
keywords: C4 metabolic model; biopolymer; diurnal; mRNA; photosynthesis; polyhydroxybutyrate