title: Effects of reduced carbonic anhydrase activity on CO2 assimilation rates in Setaria viridis: a transgenic analysis.
abstract: In C4species, the major β-carbonic anhydrase (β-CA) localized in the mesophyll cytosol catalyses the hydration of CO2to HCO3-, which phosphoenolpyruvate carboxylase uses in the first step of C4photosynthesis. To address the role of CA in C4photosynthesis, we generated transgenic Setaria viridis depleted in β-CA. Independent lines were identified with as little as 13% of wild-type CA. No photosynthetic defect was observed in the transformed lines at ambient CO2partial pressure (pCO2). At low pCO2, a strong correlation between CO2assimilation rates and CA hydration rates was observed. C18O16O isotope discrimination was used to estimate the mesophyll conductance to CO2diffusion from the intercellular air space to the mesophyll cytosol (gm) in control plants, which allowed us to calculate CA activities in the mesophyll cytosol (Cm). This revealed a strong relationship between the initial slope of the response of the CO2assimilation rate to cytosolic pCO2(ACm) and cytosolic CA activity. However, the relationship between the initial slope of the response of CO2assimilation to intercellular pCO2(ACi) and cytosolic CA activity was curvilinear. This indicated that in S. viridis, mesophyll conductance may be a contributing limiting factor alongside CA activity to CO2assimilation rates at low pCO2.
authors.affiliation: Australian Research Council Centre of Excellence for Translational Photosynthesis, Division of Plant Sciences, Research School of Biology, The Australian National University, Acton, ACT 2601, Australia.
authors.forename: Hannah L
authors.initials: HL
authors.lastname: Osborn
authors.affiliation: Australian Research Council Centre of Excellence for Translational Photosynthesis, Division of Plant Sciences, Research School of Biology, The Australian National University, Acton, ACT 2601, Australia Hugo.Alonso@anu.edu.au.
authors.forename: Hugo
authors.identifier: 0000-0002-5462-5861
authors.initials: H
authors.lastname: Alonso-Cantabrana
authors.affiliation: Australian Research Council Centre of Excellence for Translational Photosynthesis, Division of Plant Sciences, Research School of Biology, The Australian National University, Acton, ACT 2601, Australia.
authors.forename: Robert E
authors.initials: RE
authors.lastname: Sharwood
authors.affiliation: Department of Plant Sciences, University of Cambridge, Cambridge CB2 3EA, UK.
authors.forename: Sarah
authors.initials: S
authors.lastname: Covshoff
authors.affiliation: Australian Research Council Centre of Excellence for Translational Photosynthesis, Division of Plant Sciences, Research School of Biology, The Australian National University, Acton, ACT 2601, Australia.
authors.forename: John R
authors.initials: JR
authors.lastname: Evans
authors.affiliation: Australian Research Council Centre of Excellence for Translational Photosynthesis, Division of Plant Sciences, Research School of Biology, The Australian National University, Acton, ACT 2601, Australia.
authors.forename: Robert T
authors.initials: RT
authors.lastname: Furbank
authors.affiliation: Australian Research Council Centre of Excellence for Translational Photosynthesis, Division of Plant Sciences, Research School of Biology, The Australian National University, Acton, ACT 2601, Australia.
authors.forename: Susanne
authors.initials: S
authors.lastname: von Caemmerer
mesh_terms: D002245:Carbon Dioxide / Q000378:metabolism*; D002256:Carbonic Anhydrases / Q000235:genetics / Q000378:metabolism*; D058503:Mesophyll Cells / Q000502:physiology*; D010103:Oxygen Isotopes / Q000378:metabolism; D010788:Photosynthesis; D018526:Plant Transpiration; D030821:Plants, Genetically Modified; D032983:Setaria Plant / Q000201:enzymology* / Q000235:genetics
chemical_list: D010103:Oxygen Isotopes; D002245:Carbon Dioxide; D002256:Carbonic Anhydrases
keywords: C18O16O isotope discrimination; C4 photosynthesis; Carbonic anhydrase; Setaria viridis; mesophyll conductance; transformation