title: Transplastomic integration of a cyanobacterial bicarbonate transporter into tobacco chloroplasts.
abstract: Improving global yields of agricultural crops is a complex challenge with evidence indicating benefits in productivity are achieved by enhancing photosynthetic carbon assimilation. Towards improving rates of CO2 capture within leaf chloroplasts, this study shows the versatility of plastome transformation for expressing the Synechococcus PCC7002 BicA bicarbonate transporter within tobacco plastids. Fractionation of chloroplast membranes from transplastomic tob(BicA) lines showed that ~75% of the BicA localized to the thylakoid membranes and ~25% to the chloroplast envelope. BicA levels were highest in young emerging tob(BicA) leaves (0.12 μmol m(-2), ≈7mg m(-2)) accounting for ~0.1% (w/w) of the leaf protein. In these leaves, the molar amount of BicA was 16-fold lower than the abundant thylakoid photosystem II D1 protein (~1.9 μmol m(-2)) which was comparable to the 9:1 molar ratio of D1:BicA measured in air-grown Synechococcus PCC7002 cells. The BicA produced had no discernible effect on chloroplast ultrastructure, photosynthetic CO2-assimilation rates, carbon isotope discrimination, or growth of the tob(BicA) plants, implying that the bicarbonate transporter had little or no activity. These findings demonstrate the utility of plastome transformation for targeting bicarbonate transporter proteins into the chloroplast membranes without impeding growth or plastid ultrastructure. This study establishes the span of experimental measurements required to verify heterologous bicarbonate transporter function and location in chloroplasts and underscores the need for more detailed understanding of BicA structure and function to identify solutions for enabling its activation and operation in leaf chloroplasts.
authors: Plant Science Division, Research School of Biology, The Australian National University, Canberra, ACT 0200, Australia.
authors: J J L
authors: JJ
authors: Pengelly
authors: Plant Science Division, Research School of Biology, The Australian National University, Canberra, ACT 0200, Australia.
authors: B
authors: B
authors: Förster
authors: Plant Science Division, Research School of Biology, The Australian National University, Canberra, ACT 0200, Australia.
authors: S
authors: S
authors: von Caemmerer
authors: Plant Science Division, Research School of Biology, The Australian National University, Canberra, ACT 0200, Australia.
authors: M R
authors: MR
authors: Badger
authors: Plant Science Division, Research School of Biology, The Australian National University, Canberra, ACT 0200, Australia.
authors: G D
authors: GD
authors: Price
authors: Plant Science Division, Research School of Biology, The Australian National University, Canberra, ACT 0200, Australia spencer.whitney@anu.edu.au.
authors: S M
authors: SM
authors: Whitney
mesh_terms: D027321:Anion Transport Proteins / Q000235:genetics* / Q000378:metabolism; D001639:Bicarbonates / Q000378:metabolism*; D002244:Carbon / Q000378:metabolism; D002736:Chloroplasts / Q000378:metabolism / Q000648:ultrastructure; D005240:Feasibility Studies; D015151:Immunoblotting; D046529:Microscopy, Electron, Transmission; D010788:Photosynthesis; D018515:Plant Leaves / Q000378:metabolism; D030821:Plants, Genetically Modified / Q000235:genetics / Q000378:metabolism; D046940:Synechococcus / Q000235:genetics* / Q000378:metabolism; D014026:Nicotiana / Q000235:genetics* / Q000378:metabolism
chemical_list: D027321:Anion Transport Proteins; D001639:Bicarbonates; D002244:Carbon
keywords: Bicarbonate pumps; CO2-concentrating mechanism; chloroplast envelope; crop improvement; cyanobacteria; photosynthetic efficiency; plastome transformation.