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Rao S, Liu T, Cernusak LA, Song X. Harnessing photosynthetic C 18O 16O discrimination dynamics under leaf water nonsteady state to estimate mesophyll conductance: a new, regression-based method. THE NEW PHYTOLOGIST 2024; 243:2102-2114. [PMID: 38634162 DOI: 10.1111/nph.19767] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/13/2023] [Accepted: 03/27/2024] [Indexed: 04/19/2024]
Abstract
Mesophyll conductance (gm) is a crucial plant trait that can significantly limit photosynthesis. Measurement of photosynthetic C18O16O discrimination (Δ18O) has proved to be the only viable means of resolving gm in both C3 and C4 plants. However, the currently available methods to exploit Δ18O for gm estimation are error prone due to their inadequacy in constraining the degree of oxygen isotope exchange (θ) during mesophyll CO2 hydration. Here, we capitalized on experimental manipulation of leaf water isotopic dynamics to establish a novel, nonsteady state, regression-based approach for simultaneous determination of gm and θ from online Δ18O measurements. We demonstrated the methodological and theoretical robustness of this new Δ18O-gm estimation approach and showed through measurements on several C3 and C4 species that this approach can serve as a benchmark method against which to identify previously-unrecognized biases of the existing Δ18O-gm methods. Our results highlight the unique value of this nonsteady state-based approach for contributing to ongoing efforts toward quantitative understanding of mesophyll conductance for crop yield improvement and carbon cycle modeling.
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Affiliation(s)
- Sen Rao
- College of Life Sciences and Oceanography, Shenzhen University, Shenzhen, 518060, China
- Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Optoelectronic Engineering, Shenzhen University, Shenzhen, 518060, China
| | - Tao Liu
- College of Resources, Sichuan Agricultural University, Chengdu, 611130, China
| | - Lucas A Cernusak
- College of Science and Engineering, James Cook University, Cairns, Qld, 4878, Australia
| | - Xin Song
- College of Life Sciences and Oceanography, Shenzhen University, Shenzhen, 518060, China
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2
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Bellasio C, Lundgren MR. The operation of PEPCK increases light harvesting plasticity in C 4 NAD-ME and NADP-ME photosynthetic subtypes: A theoretical study. PLANT, CELL & ENVIRONMENT 2024; 47:2288-2309. [PMID: 38494958 DOI: 10.1111/pce.14869] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/10/2022] [Revised: 02/15/2024] [Accepted: 02/18/2024] [Indexed: 03/19/2024]
Abstract
The repeated emergence of NADP-malic enzyme (ME), NAD-ME and phosphoenolpyruvate carboxykinase (PEPCK) subtypes of C4 photosynthesis are iconic examples of convergent evolution, which suggests that these biochemistries do not randomly assemble, but are instead specific adaptations resulting from unknown evolutionary drivers. Theoretical studies that are based on the classic biochemical understanding have repeatedly proposed light-use efficiency as a possible benefit of the PEPCK subtype. However, quantum yield measurements do not support this idea. We explore this inconsistency here via an analytical model that features explicit descriptions across a seamless gradient between C4 biochemistries to analyse light harvesting and dark photosynthetic metabolism. Our simulations show that the NADP-ME subtype, operated by the most productive crops, is the most efficient. The NAD-ME subtype has lower efficiency, but has greater light harvesting plasticity (the capacity to assimilate CO2 in the broadest combination of light intensity and spectral qualities). In both NADP-ME and NAD-ME backgrounds, increasing PEPCK activity corresponds to greater light harvesting plasticity but likely imposed a reduction in photosynthetic efficiency. We draw the first mechanistic links between light harvesting and C4 subtypes, providing the theoretical basis for future investigation.
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Affiliation(s)
- Chandra Bellasio
- Laboratory of Theoretical and Applied Crop Ecophysiology, School of Biology and Environmental Science, University College Dublin, Dublin, Ireland
- Department of Chemistry, Biology ond Biotechnology, Università Degli Studi Di Perugia, Perugia, Italy
- Department of Biology, University of the Balearic Islands, Palma, Illes Balears, Spain
- Research School of Biology, Australian National University, Canberra, Australian Capital Territory, Australia
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3
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Zhou L, Xiang X, Ji D, Chen Q, Ma T, Wang J, Liu C. A Carbonic Anhydrase, ZmCA4, Contributes to Photosynthetic Efficiency and Modulates CO2 Signaling Gene Expression by Interacting with Aquaporin ZmPIP2;6 in Maize. PLANT & CELL PHYSIOLOGY 2024; 65:243-258. [PMID: 37955399 DOI: 10.1093/pcp/pcad145] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/30/2023] [Revised: 11/07/2023] [Accepted: 11/10/2023] [Indexed: 11/14/2023]
Abstract
Carbonic anhydrase (CA) catalyzes the reversible CO2 hydration reaction that produces bicarbonate for phosphoenolpyruvate carboxylase (PEPC). This is the initial step for transmitting the CO2 signal in C4 photosynthesis. However, it remains unknown whether the maize (Zea mays L.) CA gene, ZmCA4, plays a role in the maize photosynthesis process. In our study, we found that ZmCA4 was relatively highly expressed in leaves and localized in the chloroplast and the plasma membrane of mesophyll protoplasts. Knock-out of ZmCA4 reduced CA activity, while overexpression of ZmCA4 increased rubisco activity, as well as the quantum yield and relative electron transport rate in photosystem II. Overexpression of ZmCA4 enhanced maize yield-related traits. Moreover, ZmCA4 interacted with aquaporin ZmPIP2;6 in bimolecular fluorescence complementation and co-immunoprecipitation experiments. The double-knock-out mutant for ZmPIP2;6 and ZmCA4 genes showed reductions in its growth, CA and PEPC activities, assimilation rate and photosystem activity. RNA-Seq analysis revealed that the expression of other ZmCAs, ZmPIPs, as well as CO2 signaling pathway homologous genes, and photosynthetic-related genes was all altered in the double-knock-out mutant compared with the wild type. Altogether, our study's findings point to a critical role of ZmCA4 in determining photosynthetic capacity and modulating CO2 signaling regulation via its interaction with ZmPIP2;6, thus providing insight into the potential genetic value of ZmCA4 for maize yield improvement.
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Affiliation(s)
- Lian Zhou
- Maize Research Institute, College of Agronomy and Biotechnology, Southwest University, No. 2 Tiansheng Road, Beibei, Chongqing 400715, China
- Engineering Research Center of South Upland Agriculture, Ministry of Education, No. 2 Tiansheng Road, Beibei, Chongqing 400715, China
| | - Xiaoqin Xiang
- Maize Research Institute, College of Agronomy and Biotechnology, Southwest University, No. 2 Tiansheng Road, Beibei, Chongqing 400715, China
| | - Dongpu Ji
- Maize Research Institute, College of Agronomy and Biotechnology, Southwest University, No. 2 Tiansheng Road, Beibei, Chongqing 400715, China
| | - Qiulan Chen
- Maize Research Institute, College of Agronomy and Biotechnology, Southwest University, No. 2 Tiansheng Road, Beibei, Chongqing 400715, China
| | - Tengfei Ma
- Maize Research Institute, College of Agronomy and Biotechnology, Southwest University, No. 2 Tiansheng Road, Beibei, Chongqing 400715, China
| | - Jiuguang Wang
- Maize Research Institute, College of Agronomy and Biotechnology, Southwest University, No. 2 Tiansheng Road, Beibei, Chongqing 400715, China
- Engineering Research Center of South Upland Agriculture, Ministry of Education, No. 2 Tiansheng Road, Beibei, Chongqing 400715, China
| | - Chaoxian Liu
- Maize Research Institute, College of Agronomy and Biotechnology, Southwest University, No. 2 Tiansheng Road, Beibei, Chongqing 400715, China
- Engineering Research Center of South Upland Agriculture, Ministry of Education, No. 2 Tiansheng Road, Beibei, Chongqing 400715, China
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Ubierna N, Holloway-Phillips MM, Wingate L, Ogée J, Busch FA, Farquhar GD. Using Carbon Stable Isotopes to Study C 3 and C 4 Photosynthesis: Models and Calculations. Methods Mol Biol 2024; 2790:163-211. [PMID: 38649572 DOI: 10.1007/978-1-0716-3790-6_10] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/25/2024]
Abstract
Stable carbon isotopes are a powerful tool to study photosynthesis. Initial applications consisted of determining isotope ratios of plant biomass using mass spectrometry. Subsequently, theoretical models relating C isotope values to gas exchange characteristics were introduced and tested against instantaneous online measurements of 13C photosynthetic discrimination. Beginning in the twenty-first century, laser absorption spectroscopes with sufficient precision for determining isotope mixing ratios became commercially available. This has allowed collection of large data sets at lower cost and with unprecedented temporal resolution. More data and accompanying knowledge have permitted refinement of 13C discrimination model equations, but often at the expense of increased model complexity and difficult parametrization. This chapter describes instantaneous online measurements of 13C photosynthetic discrimination, provides recommendations for experimental setup, and presents a thorough compilation of equations available to researchers. We update our previous 2018 version of this chapter by including recently improved descriptions of (photo)respiratory processes and associated fractionations. We discuss the capabilities and limitations of the diverse 13C discrimination model equations and provide guidance for selecting the model complexity needed for different applications.
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Affiliation(s)
- Nerea Ubierna
- Institut National de Recherche pour l'Agriculture, l'Alimentation et l'Environnement (INRAE), Unité Mixte de Recherche (UMR)1391 ISPA, Villenave D'Ornon, France
| | - Meisha-Marika Holloway-Phillips
- Research Unit of Forest Dynamics, Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Birmendsorf, Switzerland
| | - Lisa Wingate
- Institut National de Recherche pour l'Agriculture, l'Alimentation et l'Environnement (INRAE), Unité Mixte de Recherche (UMR)1391 ISPA, Villenave D'Ornon, France
| | - Jérôme Ogée
- Institut National de Recherche pour l'Agriculture, l'Alimentation et l'Environnement (INRAE), Unité Mixte de Recherche (UMR)1391 ISPA, Villenave D'Ornon, France
| | - Florian A Busch
- School of Biosciences and The Birmingham Institute of Forest Research, University of Birmingham, Birmingham, UK
| | - Graham D Farquhar
- Research School of Biology, Australian National University, Canberra, ACT, Australia
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5
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Sagun JV, Chow WS, Ghannoum O. Leaf pigments and photosystems stoichiometry underpin photosynthetic efficiency of related C 3 , C-C 4 and C 4 grasses under shade. PHYSIOLOGIA PLANTARUM 2022; 174:e13819. [PMID: 36344438 DOI: 10.1111/ppl.13819] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/24/2022] [Revised: 09/12/2022] [Accepted: 10/31/2022] [Indexed: 06/16/2023]
Abstract
The quantum yield of photosynthesis (QY, CO2 fixed per light absorbed) depends on the efficiency of light absorption, the coupling between light absorption and electron transport, and the coupling between electron transport and carbon metabolism. QY is generally lower in C3 relative to C4 plants at warm temperatures and differs among the C4 subtypes. We investigated the acclimation to shade of light absorption and electron transport in six representative grasses with C3 , C3 -C4 and C4 photosynthesis. Plants were grown under full (control) or 25% (shade) sunlight. We measured the in vivo activity and stoichiometry of PSI and PSII, leaf spectral properties and pigment contents, and photosynthetic enzyme activities. Under control growth-light conditions, C4 species had higher CO2 assimilation rates, which declined to a greater extent relative to the C3 species. Whole leaf PSII/PSI ratios were highest in the C3 species, while QY and cyclic electron flow (CEF) were highest in the C4 , NADP-ME species. Shade significantly reduced leaf PSII/PSI, linear electron flow (LEF) and CEF of most species. Overall, shade reduced leaf absorptance, especially in the green region, as well as carotenoid and chlorophyll contents in C4 more than non-C4 species. The NAD-ME species underwent the greatest reduction in leaf absorptance and pigments under shade. In conclusion, shade compromised QY the least in the C3 and the most in the C4 -NAD-ME species. Different sensitivity to shade was associated with the ability to maintain leaf absorptance and pigments. This is important for maximising light absorption and minimising photoprotection under low light.
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Affiliation(s)
- Julius Ver Sagun
- ARC Centre of Excellence for Translational Photosynthesis, Hawkesbury Institute for the Environment, Western Sydney University, Penrith, Australia
| | - Wah Soon Chow
- ARC Centre of Excellence for Translational Photosynthesis, Research School of Biology, Australian National University, Canberra, Australia
| | - Oula Ghannoum
- ARC Centre of Excellence for Translational Photosynthesis, Hawkesbury Institute for the Environment, Western Sydney University, Penrith, Australia
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6
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Medeiros DB, Ishihara H, Guenther M, Rosado de Souza L, Fernie AR, Stitt M, Arrivault S. 13CO2 labeling kinetics in maize reveal impaired efficiency of C4 photosynthesis under low irradiance. PLANT PHYSIOLOGY 2022; 190:280-304. [PMID: 35751609 PMCID: PMC9434203 DOI: 10.1093/plphys/kiac306] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/31/2022] [Accepted: 06/06/2022] [Indexed: 06/01/2023]
Abstract
C4 photosynthesis allows faster photosynthetic rates and higher water and nitrogen use efficiency than C3 photosynthesis, but at the cost of lower quantum yield due to the energy requirement of its biochemical carbon concentration mechanism. It has also been suspected that its operation may be impaired in low irradiance. To investigate fluxes under moderate and low irradiance, maize (Zea mays) was grown at 550 µmol photons m-2 s-l and 13CO2 pulse-labeling was performed at growth irradiance or several hours after transfer to 160 µmol photons m-2 s-1. Analysis by liquid chromatography/tandem mass spectrometry or gas chromatography/mass spectrometry provided information about pool size and labeling kinetics for 32 metabolites and allowed estimation of flux at many steps in C4 photosynthesis. The results highlighted several sources of inefficiency in low light. These included excess flux at phosphoenolpyruvate carboxylase, restriction of decarboxylation by NADP-malic enzyme, and a shift to increased CO2 incorporation into aspartate, less effective use of metabolite pools to drive intercellular shuttles, and higher relative and absolute rates of photorespiration. The latter provides evidence for a lower bundle sheath CO2 concentration in low irradiance, implying that operation of the CO2 concentration mechanism is impaired in this condition. The analyses also revealed rapid exchange of carbon between the Calvin-Benson cycle and the CO2-concentration shuttle, which allows rapid adjustment of the balance between CO2 concentration and assimilation, and accumulation of large amounts of photorespiratory intermediates in low light that provides a major carbon reservoir to build up C4 metabolite pools when irradiance increases.
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Affiliation(s)
- David B Medeiros
- Max Planck Institute of Molecular Plant Physiology, 14476 Potsdam-Golm, Germany
| | - Hirofumi Ishihara
- Max Planck Institute of Molecular Plant Physiology, 14476 Potsdam-Golm, Germany
| | - Manuela Guenther
- Max Planck Institute of Molecular Plant Physiology, 14476 Potsdam-Golm, Germany
| | | | - Alisdair R Fernie
- Max Planck Institute of Molecular Plant Physiology, 14476 Potsdam-Golm, Germany
| | - Mark Stitt
- Max Planck Institute of Molecular Plant Physiology, 14476 Potsdam-Golm, Germany
| | - Stéphanie Arrivault
- Max Planck Institute of Molecular Plant Physiology, 14476 Potsdam-Golm, Germany
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7
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DiMario RJ, Giuliani R, Ubierna N, Slack AD, Cousins AB, Studer AJ. Lack of leaf carbonic anhydrase activity eliminates the C 4 carbon-concentrating mechanism requiring direct diffusion of CO 2 into bundle sheath cells. PLANT, CELL & ENVIRONMENT 2022; 45:1382-1397. [PMID: 35233800 DOI: 10.1111/pce.14291] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/19/2021] [Revised: 10/13/2021] [Accepted: 10/30/2021] [Indexed: 06/14/2023]
Abstract
Carbonic anhydrase (CA) performs the first enzymatic step of C4 photosynthesis by catalysing the reversible hydration of dissolved CO2 that diffuses into mesophyll cells from intercellular airspaces. This CA-catalysed reaction provides the bicarbonate used by phosphoenolpyruvate carboxylase to generate products that flow into the C4 carbon-concentrating mechanism (CCM). It was previously demonstrated that the Zea mays ca1ca2 double mutant lost 97% of leaf CA activity, but there was little difference in the growth phenotype under ambient CO2 partial pressures (pCO2 ). We hypothesise that since CAs are among the fastest enzymes, minimal activity from a third CA, CA8, can provide the inorganic carbon needed to drive C4 photosynthesis. We observed that removing CA8 from the maize ca1ca2 background resulted in plants that had 0.2% of wild-type leaf CA activity. These ca1ca2ca8 plants had reduced photosynthetic parameters and could only survive at elevated pCO2 . Photosynthetic and carbon isotope analysis combined with modelling of photosynthesis and carbon isotope discrimination was used to determine if ca1ca2ca8 plants had a functional C4 cycle or were relying on direct CO2 diffusion to ribulose 1,5-bisphosphate carboxylase/oxygenase within bundle sheath cells. The results suggest that leaf CA activity in ca1ca2ca8 plants was not sufficient to sustain the C4 CCM.
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Affiliation(s)
- Robert J DiMario
- School of Biological Sciences, Washington State University, Pullman, Washington, USA
| | - Rita Giuliani
- School of Biological Sciences, Washington State University, Pullman, Washington, USA
| | - Nerea Ubierna
- School of Biological Sciences, Washington State University, Pullman, Washington, USA
| | - Aaron D Slack
- Department of Crop Sciences, University of Illinois Urbana-Champaign, Urbana, Illinois, USA
| | - Asaph B Cousins
- School of Biological Sciences, Washington State University, Pullman, Washington, USA
| | - Anthony J Studer
- Department of Crop Sciences, University of Illinois Urbana-Champaign, Urbana, Illinois, USA
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8
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Understanding the Relationship between Water Availability and Biosilica Accumulation in Selected C4 Crop Leaves: An Experimental Approach. PLANTS 2022; 11:plants11081019. [PMID: 35448747 PMCID: PMC9031050 DOI: 10.3390/plants11081019] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/15/2022] [Revised: 04/01/2022] [Accepted: 04/01/2022] [Indexed: 11/16/2022]
Abstract
Biosilica accumulation in plant tissues is related to the transpiration stream, which in turn depends on water availability. Nevertheless, the debate on whether genetically and environmentally controlled mechanisms of biosilica deposition are directly connected to water availability is still open. We aim at clarifying the system which leads to the deposition of biosilica in Sorghum bicolor, Pennisetum glaucum, and Eleusine coracana, expanding our understanding of the physiological role of silicon in crops well-adapted to arid environments, and simultaneously advancing the research in archaeological and paleoenvironmental studies. We cultivated ten traditional landraces for each crop in lysimeters, simulating irrigated and rain-fed scenarios in arid contexts. The percentage of biosilica accumulated in leaves indicates that both well-watered millet species deposited more biosilica than the water-stressed ones. By contrast, sorghum accumulated more biosilica with respect to the other two species, and biosilica accumulation was independent of the water regime. The water treatment alone did not explain either the variability of the assemblage or the differences in the biosilica accumulation. Hence, we hypothesize that genetics influence the variability substantially. These results demonstrate that biosilica accumulation differs among and within C4 species and that water availability is not the only driver in this process.
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9
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Crawford JD, Cousins AB. Limitation of C4 photosynthesis by low carbonic anhydrase activity increases with temperature but does not influence mesophyll CO2 conductance. JOURNAL OF EXPERIMENTAL BOTANY 2022; 73:927-938. [PMID: 34698863 DOI: 10.1093/jxb/erab464] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/23/2021] [Accepted: 10/23/2021] [Indexed: 06/13/2023]
Abstract
The CO2-concentrating mechanism (CCM) in C4 plants is initiated by the uptake of bicarbonate (HCO3-) via phosphoenolpyruvate carboxylase (PEPC). Generation of HCO3- for PEPC is determined by the interaction between mesophyll CO2 conductance and the hydration of CO2 to HCO3- by carbonic anhydrase (CA). Genetic reduction of CA was previously shown not to limit C4 photosynthesis under ambient atmospheric partial pressures of CO2 (pCO2). However, CA activity varies widely across C4 species and it is unknown if there are specific environmental conditions (e.g. high temperature) where CA may limit HCO3- production for C4 photosynthesis. Additionally, CA activity has been suggested to influence mesophyll conductance, but this has not been experimentally tested. We hypothesize that CA activity can limit PEPC at high temperatures, particularly at low pCO2, but does not directly influence gm. Here we tested the influence of genetically reduced CA activity on photosynthesis and gm in the C4 plant Zea mays under a range of pCO2 and temperatures. Reduced CA activity limited HCO3- production for C4 photosynthesis at low pCO2 as temperatures increased, but did not influence mesophyll conductance. Therefore, high leaf CA activity may enhance C4 photosynthesis under high temperature when stomatal conductance restricts the availability of atmospheric CO2.
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Affiliation(s)
- Joseph D Crawford
- School of Biological Sciences, Washington State University, Pullman, WA, USA
| | - Asaph B Cousins
- School of Biological Sciences, Washington State University, Pullman, WA, USA
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von Caemmerer S. Updating the steady-state model of C4 photosynthesis. JOURNAL OF EXPERIMENTAL BOTANY 2021; 72:6003-6017. [PMID: 34173821 PMCID: PMC8411607 DOI: 10.1093/jxb/erab266] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/04/2021] [Accepted: 06/06/2021] [Indexed: 05/22/2023]
Abstract
C4 plants play a key role in world agriculture. For example, C4 crops such as maize and sorghum are major contributors to food production in both developed and developing countries, and the C4 grasses sugarcane, miscanthus, and switchgrass are major plant sources of bioenergy. In the challenge to manipulate and enhance C4 photosynthesis, steady-state models of leaf photosynthesis provide an important tool for gas exchange analysis and thought experiments that can explore photosynthetic pathway changes. Here a previous C4 photosynthetic model developed by von Caemmerer and Furbank has been updated with new kinetic parameterization and temperature dependencies added. The parameterization was derived from experiments on the C4 monocot, Setaria viridis, which for the first time provides a cohesive parameterization. Mesophyll conductance and its temperature dependence have also been included, as this is an important step in the quantitative correlation between the initial slope of the CO2 response curve of CO2 assimilation and in vitro phosphoenolpyruvate carboxylase activity. Furthermore, the equations for chloroplast electron transport have been updated to include cyclic electron transport flow, and equations have been added to calculate the electron transport rate from measured CO2 assimilation rates.
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Affiliation(s)
- Susanne von Caemmerer
- 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
- Correspondence:
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11
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Eggels S, Blankenagel S, Schön CC, Avramova V. The carbon isotopic signature of C 4 crops and its applicability in breeding for climate resilience. TAG. THEORETICAL AND APPLIED GENETICS. THEORETISCHE UND ANGEWANDTE GENETIK 2021; 134:1663-1675. [PMID: 33575820 PMCID: PMC8205923 DOI: 10.1007/s00122-020-03761-3] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/05/2020] [Accepted: 12/30/2020] [Indexed: 05/04/2023]
Abstract
KEY MESSAGE Carbon isotope discrimination is a promising trait for indirect screening for improved water use efficiency of C4 crops. In the context of a changing climate, drought is one of the major factors limiting plant growth and yield. Hence, breeding efforts are directed toward improving water use efficiency (WUE) as a key factor in climate resilience and sustainability of crop production. As WUE is a complex trait and its evaluation is rather resource consuming, proxy traits, which are easier to screen and reliably reflect variation in WUE, are needed. In C3 crops, a trait established to be indicative for WUE is the carbon isotopic composition (δ13C) of plant material, which reflects the preferential assimilation of the lighter carbon isotope 12C over 13C during photosynthesis. In C4 crops, carbon fixation is more complex and δ13C thus depends on many more factors than in C3 crops. Recent physiological and genetic studies indicate a correlation between δ13C and WUE also in C4 crops, as well as a colocalization of quantitative trait loci for the two traits. Moreover, significant intraspecific variation as well as a medium to high heritability of δ13C has been shown in some of the main C4 crops, such as maize, sorghum and sugarcane, indicating its potential for indirect selection and breeding. Further research on physiological, genetic and environmental components influencing δ13C is needed to support its application in improving WUE and making C4 crops resilient to climate change.
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Affiliation(s)
- Stella Eggels
- Plant Breeding, TUM School of Life Sciences, Technical University of Munich, Liesel-Beckmann-Straße 2, 85354, Freising, Germany
| | - Sonja Blankenagel
- Plant Breeding, TUM School of Life Sciences, Technical University of Munich, Liesel-Beckmann-Straße 2, 85354, Freising, Germany
| | - Chris-Carolin Schön
- Plant Breeding, TUM School of Life Sciences, Technical University of Munich, Liesel-Beckmann-Straße 2, 85354, Freising, Germany
| | - Viktoriya Avramova
- Plant Breeding, TUM School of Life Sciences, Technical University of Munich, Liesel-Beckmann-Straße 2, 85354, Freising, Germany.
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12
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Chatterjee J, Coe RA, Acebron K, Thakur V, Yennamalli RM, Danila F, Lin HC, Balahadia CP, Bagunu E, Padhma PPOS, Bala S, Yin X, Rizal G, Dionora J, Furbank RT, von Caemmerer S, Quick WP. A low CO2-responsive mutant of Setaria viridis reveals that reduced carbonic anhydrase limits C4 photosynthesis. JOURNAL OF EXPERIMENTAL BOTANY 2021; 72:3122-3136. [PMID: 33528493 PMCID: PMC8023212 DOI: 10.1093/jxb/erab039] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/14/2020] [Accepted: 01/30/2021] [Indexed: 06/12/2023]
Abstract
In C4 species, β-carbonic anhydrase (CA), localized to the cytosol of the mesophyll cells, accelerates the interconversion of CO2 to HCO3-, the substrate used by phosphoenolpyruvate carboxylase (PEPC) in the first step of C4 photosynthesis. Here we describe the identification and characterization of low CO2-responsive mutant 1 (lcr1) isolated from an N-nitroso-N-methylurea- (NMU) treated Setaria viridis mutant population. Forward genetic investigation revealed that the mutated gene Sevir.5G247800 of lcr1 possessed a single nucleotide transition from cytosine to thymine in a β-CA gene causing an amino acid change from leucine to phenylalanine. This resulted in severe reduction in growth and photosynthesis in the mutant. Both the CO2 compensation point and carbon isotope discrimination values of the mutant were significantly increased. Growth of the mutants was stunted when grown under ambient pCO2 but recovered at elevated pCO2. Further bioinformatics analyses revealed that the mutation has led to functional changes in one of the conserved residues of the protein, situated near the catalytic site. CA transcript accumulation in the mutant was 80% lower, CA protein accumulation 30% lower, and CA activity ~98% lower compared with the wild type. Changes in the abundance of other primary C4 pathway enzymes were observed; accumulation of PEPC protein was significantly increased and accumulation of malate dehydrogenase and malic enzyme decreased. The reduction of CA protein activity and abundance in lcr1 restricts the supply of bicarbonate to PEPC, limiting C4 photosynthesis and growth. This study establishes Sevir.5G247800 as the major CA allele in Setaria for C4 photosynthesis and provides important insights into the function of CA in C4 photosynthesis that would be required to generate a rice plant with a functional C4 biochemical pathway.
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Affiliation(s)
- Jolly Chatterjee
- C4 Rice Centre, International Rice Research Institute (IRRI), Los Baños, Philippines
| | - Robert A Coe
- CSIRO Agriculture Flagship, Australian Plant Phenomics Facility, GPO Box 1500, Canberra, ACT 2601, Australia
| | - Kelvin Acebron
- C4 Rice Centre, International Rice Research Institute (IRRI), Los Baños, Philippines
| | - Vivek Thakur
- C4 Rice Centre, International Rice Research Institute (IRRI), Los Baños, Philippines
- Department of Systems & Computational Biology, School of Life Sciences, University of Hyderabad, Hyderabad-500046, India
| | - Ragothaman M Yennamalli
- Department of Bioinformatics, School of Chemical and Biotechnology, SASTRA Deemed to be University, Thanjavur, Tamilnadu-613401, India
| | - Florence Danila
- ARC Centre of Excellence for Translational Photosynthesis, Research School of Biology, Australian National University, GPO Box 1500, Canberra, ACT 2601, Australia
| | - Hsiang-Chun Lin
- C4 Rice Centre, International Rice Research Institute (IRRI), Los Baños, Philippines
| | | | - Efren Bagunu
- C4 Rice Centre, International Rice Research Institute (IRRI), Los Baños, Philippines
| | - Preiya P O S Padhma
- Department of Systems & Computational Biology, School of Life Sciences, University of Hyderabad, Hyderabad-500046, India
| | - Soumi Bala
- ARC Centre of Excellence for Translational Photosynthesis, Research School of Biology, Australian National University, GPO Box 1500, Canberra, ACT 2601, Australia
| | - Xiaojia Yin
- C4 Rice Centre, International Rice Research Institute (IRRI), Los Baños, Philippines
| | - Govinda Rizal
- C4 Rice Centre, International Rice Research Institute (IRRI), Los Baños, Philippines
| | - Jacqueline Dionora
- C4 Rice Centre, International Rice Research Institute (IRRI), Los Baños, Philippines
| | - Robert T Furbank
- ARC Centre of Excellence for Translational Photosynthesis, Research School of Biology, Australian National University, GPO Box 1500, Canberra, ACT 2601, Australia
| | - Susanne von Caemmerer
- ARC Centre of Excellence for Translational Photosynthesis, Research School of Biology, Australian National University, GPO Box 1500, Canberra, ACT 2601, Australia
| | - William Paul Quick
- C4 Rice Centre, International Rice Research Institute (IRRI), Los Baños, Philippines
- Department of Animal and Plant Sciences, University of Sheffield, Sheffield S10 2TN, UK
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13
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Pignon CP, Long SP. Retrospective analysis of biochemical limitations to photosynthesis in 49 species: C 4 crops appear still adapted to pre-industrial atmospheric [CO 2 ]. PLANT, CELL & ENVIRONMENT 2020; 43:2606-2622. [PMID: 32743797 DOI: 10.1111/pce.13863] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/02/2020] [Revised: 06/23/2020] [Accepted: 07/24/2020] [Indexed: 06/11/2023]
Abstract
Leaf CO2 uptake (A) in C4 photosynthesis is limited by the maximum apparent rate of PEPc carboxylation (Vpmax ) at low intercellular [CO2 ] (ci ) with a sharp transition to a ci -saturated rate (Vmax ) due to co-limitation by ribulose-1:5-bisphosphate carboxylase/oxygenase (Rubisco) and regeneration of PEP. The response of A to ci has been widely used to determine these two parameters. Vmax and Vpmax depend on different enzymes but draw on a shared pool of leaf resources, such that resource distribution is optimized, and A maximized, when Vmax and Vpmax are co-limiting. We collected published A/ci curves in 49 C4 species and assessed variation in photosynthetic traits between phylogenetic groups, and as a function of atmospheric [CO2 ]. The balance of Vmax -Vpmax varied among evolutionary lineages and C4 subtypes. Operating A was strongly Vmax -limited, such that re-allocation of resources from Vpmax towards Vmax was predicted to improve A by 12% in C4 crops. This would not require additional inputs but rather altered partitioning of existing leaf nutrients, resulting in increased water and nutrient-use efficiency. Optimal partitioning was achieved only in plants grown at pre-industrial atmospheric [CO2 ], suggesting C4 crops have not adjusted to the rapid increase in atmospheric [CO2 ] of the past few decades.
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Affiliation(s)
- Charles P Pignon
- Carl Woese Institute for Genomic Biology and Departments of Crop Sciences and Plant Biology, University of Illinois, Urbana, Illinois, USA
| | - Stephen P Long
- Carl Woese Institute for Genomic Biology and Departments of Crop Sciences and Plant Biology, University of Illinois, Urbana, Illinois, USA
- Lancaster Environment Centre, University of Lancaster, UK
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14
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Lightfoot E, Ustunkaya MC, Przelomska N, O'Connell TC, Hunt HV, Jones MK, Petrie CA. Carbon and nitrogen isotopic variability in foxtail millet (Setaria italica) with watering regime. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2020; 34:e8615. [PMID: 31658389 PMCID: PMC7050514 DOI: 10.1002/rcm.8615] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/18/2019] [Revised: 09/27/2019] [Accepted: 09/27/2019] [Indexed: 06/10/2023]
Abstract
RATIONALE Carbonised plant remains are analysed for reconstruction of past climates and agricultural regimes. Several recent studies have used C4 plants to address related questions, and correlations between modern C4 plant δ13 C values and rainfall have been found. The millets were important food crops in prehistoric Eurasia, yet little is known about causes of isotopic variation within millet species. Previous research has shown there to be significant isotopic variation between millet accessions. Here we compare isotope ratios from plants grown under different watering regimes. This allows for a consideration of whether or not Setaria italica is a good proxy for environmental reconstruction. METHODS We compare stable isotope ratios of Setaria italica plants grown in a controlled environment chamber with different watering regimes. We compare the carbon isotope ratios of leaves and grains, and the nitrogen isotope ratios of grains, from 12 accessions of Setaria italica. RESULTS We find significant isotopic variability between watering regimes. Carbon isotope ratios are positively correlated with water availability, and on average vary by 1.9‰ and 1.7‰ for leaves and grains, respectively. Grain nitrogen isotope ratios also vary with watering regime; however, the highest isotope ratios are found with the 130-mL watering regime. CONCLUSIONS The carbon isotope ratios of Setaria italica are strongly correlated with water availability. However, the correlation is the opposite to that seen in studies of C3 plants. The difference in isotopic ratio due to watering regime is comparable with that seen between different accessions; thus distinguishing between changing varieties of Setaria italica and changing climate is problematic. In terms of grain nitrogen isotope ratios, the highest δ15 N values were not associated with the lowest watering regime. Again, δ15 N variation is comparable with that which would be expected from an aridity effect or a manuring effect, and thus distinguishing between these factors is probably problematic.
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Affiliation(s)
- Emma Lightfoot
- McDonald Institute for Archaeological ResearchUniversity of CambridgeDowning StreetCambridgeCB2 3ERUK
| | - M. Cemre Ustunkaya
- McDonald Institute for Archaeological ResearchUniversity of CambridgeDowning StreetCambridgeCB2 3ERUK
| | - Natalia Przelomska
- Department of Anthropology, National Museum of Natural HistorySmithsonian InstitutionWashingtonDC20560USA
- Center for Conservation GenomicsSmithsonian Conservation Biology InstituteNational ZooWashingtonDC20008USA
| | - Tamsin C. O'Connell
- Department of ArchaeologyUniversity of CambridgeDowning StreetCambridgeCB2 3DZUK
| | - Harriet V. Hunt
- McDonald Institute for Archaeological ResearchUniversity of CambridgeDowning StreetCambridgeCB2 3ERUK
| | - Martin K. Jones
- Department of ArchaeologyUniversity of CambridgeDowning StreetCambridgeCB2 3DZUK
| | - Cameron A. Petrie
- Department of ArchaeologyUniversity of CambridgeDowning StreetCambridgeCB2 3DZUK
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15
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Cousins AB, Mullendore DL, Sonawane BV. Recent developments in mesophyll conductance in C3, C4, and crassulacean acid metabolism plants. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2020; 101:816-830. [PMID: 31960507 DOI: 10.1111/tpj.14664] [Citation(s) in RCA: 31] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/13/2019] [Accepted: 12/19/2019] [Indexed: 05/24/2023]
Abstract
The conductance of carbon dioxide (CO2 ) from the substomatal cavities to the initial sites of CO2 fixation (gm ) can significantly reduce the availability of CO2 for photosynthesis. There have been many recent reviews on: (i) the importance of gm for accurately modelling net rates of CO2 assimilation, (ii) on how leaf biochemical and anatomical factors influence gm , (iii) the technical limitation of estimating gm , which cannot be directly measured, and (iv) how gm responds to long- and short-term changes in growth and measurement environmental conditions. Therefore, this review will highlight these previous publications but will attempt not to repeat what has already been published. We will instead initially focus on the recent developments on the two-resistance model of gm that describe the potential of photorespiratory and respiratory CO2 released within the mitochondria to diffuse directly into both the chloroplast and the cytosol. Subsequently, we summarize recent developments in the three-dimensional (3-D) reaction-diffusion models and 3-D image analysis that are providing new insights into how the complex structure and organization of the leaf influences gm . Finally, because most of the reviews and literature on gm have traditionally focused on C3 plants we review in the final sections some of the recent developments, current understanding and measurement techniques of gm in C4 and crassulacean acid metabolism (CAM) plants. These plants have both specialized leaf anatomy and either a spatially or temporally separated CO2 concentrating mechanisms (C4 and CAM, respectively) that influence how we interpret and estimate gm compared with a C3 plants.
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Affiliation(s)
- Asaph B Cousins
- School of Biological Sciences, Washington State University, Pullman, WA, 99164, USA
| | - Daniel L Mullendore
- School of Biological Sciences, Washington State University, Pullman, WA, 99164, USA
| | - Balasaheb V Sonawane
- School of Biological Sciences, Washington State University, Pullman, WA, 99164, USA
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16
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Cano FJ, Sharwood RE, Cousins AB, Ghannoum O. The role of leaf width and conductances to CO 2 in determining water use efficiency in C 4 grasses. THE NEW PHYTOLOGIST 2019; 223:1280-1295. [PMID: 31087798 DOI: 10.1111/nph.15920] [Citation(s) in RCA: 29] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/22/2019] [Accepted: 04/28/2019] [Indexed: 05/26/2023]
Abstract
C4 plants achieve higher photosynthesis (An ) and intrinsic water use efficiency (iWUE) than C3 plants, but processes underpinning the variability in An and iWUE across the three C4 subtypes remain unclear, partly because we lack an integrated framework for quantifying the contribution of diffusional and biochemical limitations to C4 photosynthesis. We exploited the natural diversity among C4 grasses to develop an original mathematical approach for estimating eight key processes of C4 photosynthesis and their relative limitations to An . We also developed a new formulation to estimate mesophyll conductance (gm ) based on actual hydration rates of CO2 by carbonic anhydrases. We found a positive relationship between gm and iWUE and an inverse correlation with gsw among C4 grasses. We also revealed subtype-specific regulatory processes of iWUE that may be related to known anatomical traits characterising each C4 subtype. Leaf width was an important determinant of iWUE and showed significant correlations with key limitations of An , especially among NADP-ME species. In conclusion, incorporating leaf width in breeding trials may unlock new opportunities for C4 crops because the revealed negative relationship between leaf width and iWUE may translate into higher crop and canopy WUE.
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Affiliation(s)
- Francisco Javier Cano
- ARC Centre of Translational Photosynthesis and Hawkesbury Institute for the Environment, Western Sydney University, Sydney, NSW, 2753, Australia
| | - Robert E Sharwood
- ARC Centre of Translational Photosynthesis and Australian National University, Research School of Biology, Acton, ACT, 2601, Australia
| | - Asaph B Cousins
- School of Biological Sciences, Washington State University, Pullman, WA 99164, USA
| | - Oula Ghannoum
- ARC Centre of Translational Photosynthesis and Hawkesbury Institute for the Environment, Western Sydney University, Sydney, NSW, 2753, Australia
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17
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Sonawane BV, Cousins AB. Uncertainties and limitations of using carbon-13 and oxygen-18 leaf isotope exchange to estimate the temperature response of mesophyll CO 2 conductance in C 3 plants. THE NEW PHYTOLOGIST 2019; 222:122-131. [PMID: 30394538 DOI: 10.1111/nph.15585] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/24/2018] [Accepted: 10/28/2018] [Indexed: 06/08/2023]
Abstract
The internal CO2 gradient imposed by mesophyll conductance (gm ) reduces substrate availability for C3 photosynthesis. With several assumptions, estimates of gm can be made from coupled leaf gas exchange with isoflux analysis of carbon ∆13 C-gm and oxygen in CO2 , coupled with transpired water (H2 O) ∆18 O-gm to partition gm into its biochemical and anatomical components. However, these assumptions require validation under changing leaf temperatures. To test these assumptions, we measured and modeled the temperature response (15-40°C) of ∆13 C-gm and ∆18 O-gm along with leaf biochemistry in the C3 grass Panicum bisulcatum, which has naturally low carbonic anhydrase activity. Our study suggests that assumptions regarding the extent of isotopic equilibrium (θ) between CO2 and H2 O at the site of exchange, and that the isotopic composition of the H2 O at the sites of evaporation ( δw-e18 ) and at the site of exchange ( δw-ce18 ) are similar, may lead to errors in estimating the ∆18 O-gm temperature response. The input parameters for ∆13 C-gm appear to be less sensitive to temperature. However, this needs to be tested in species with diverse carbonic anhydrase activity. Additional information on the temperature dependency of cytosolic and chloroplastic pH may clarify uncertainties used for ∆18 O-gm under changing leaf temperatures.
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Affiliation(s)
- Balasaheb V Sonawane
- School of Biological Sciences, Washington State University, Pullman, WA, 99164, USA
| | - Asaph B Cousins
- School of Biological Sciences, Washington State University, Pullman, WA, 99164, USA
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18
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Sonawane BV, Sharwood RE, Whitney S, Ghannoum O. Shade compromises the photosynthetic efficiency of NADP-ME less than that of PEP-CK and NAD-ME C4 grasses. JOURNAL OF EXPERIMENTAL BOTANY 2018; 69:3053-3068. [PMID: 29659931 PMCID: PMC5972597 DOI: 10.1093/jxb/ery129] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/17/2017] [Accepted: 03/19/2018] [Indexed: 05/18/2023]
Abstract
The high energy cost and apparently low plasticity of C4 photosynthesis compared with C3 photosynthesis may limit the productivity and distribution of C4 plants in low light (LL) environments. C4 photosynthesis evolved numerous times, but it remains unclear how different biochemical subtypes perform under LL. We grew eight C4 grasses belonging to three biochemical subtypes [NADP-malic enzyme (NADP-ME), NAD-malic enzyme (NAD-ME), and phosphoenolpyruvate carboxykinase (PEP-CK)] under shade (16% sunlight) or control (full sunlight) conditions and measured their photosynthetic characteristics at both low and high light. We show for the first time that LL (during measurement or growth) compromised the CO2-concentrating mechanism (CCM) to a greater extent in NAD-ME than in PEP-CK or NADP-ME C4 grasses by virtue of a greater increase in carbon isotope discrimination (∆P) and bundle sheath CO2 leakiness (ϕ), and a greater reduction in photosynthetic quantum yield (Φmax). These responses were partly explained by changes in the ratios of phosphoenolpyruvate carboxylase (PEPC)/initial Rubisco activity and dark respiration/photosynthesis (Rd/A). Shade induced a greater photosynthetic acclimation in NAD-ME than in NADP-ME and PEP-CK species due to a greater Rubisco deactivation. Shade also reduced plant dry mass to a greater extent in NAD-ME and PEP-CK relative to NADP-ME grasses. In conclusion, LL compromised the co-ordination of the C4 and C3 cycles and, hence, the efficiency of the CCM to a greater extent in NAD-ME than in PEP-CK species, while CCM efficiency was less impacted by LL in NADP-ME species. Consequently, NADP-ME species are more efficient at LL, which could explain their agronomic and ecological dominance relative to other C4 grasses.
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Affiliation(s)
- Balasaheb V Sonawane
- ARC Centre of Excellence for Translational Photosynthesis and Hawkesbury Institute for the Environment, Western Sydney University, NSW, Australia
- School of Biological Sciences, Washington State University, Pullman, WA, USA
- Correspondence:
| | - Robert E Sharwood
- ARC Centre of Excellence for Translational Photosynthesis and Research School of Biology, Australian National University, Canberra, ACT, Australia
| | - Spencer Whitney
- ARC Centre of Excellence for Translational Photosynthesis and Research School of Biology, Australian National University, Canberra, ACT, Australia
| | - Oula Ghannoum
- ARC Centre of Excellence for Translational Photosynthesis and Hawkesbury Institute for the Environment, Western Sydney University, NSW, Australia
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19
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Kolbe AR, Studer AJ, Cousins AB. Biochemical and transcriptomic analysis of maize diversity to elucidate drivers of leaf carbon isotope composition. FUNCTIONAL PLANT BIOLOGY : FPB 2018; 45:489-500. [PMID: 32290988 DOI: 10.1071/fp17265] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/08/2017] [Accepted: 11/01/2017] [Indexed: 05/13/2023]
Abstract
Carbon isotope discrimination is used to study CO2 diffusion, substrate availability for photosynthesis, and leaf biochemistry, but the intraspecific drivers of leaf carbon isotope composition (δ13C) in C4 species are not well understood. In this study, the role of photosynthetic enzymes and post-photosynthetic fractionation on δ13C (‰) was explored across diverse maize inbred lines. A significant 1.3‰ difference in δ13C was observed between lines but δ13C did not correlate with in vitro leaf carbonic anhydrase (CA), phosphoenolpyruvate carboxylase (PEPC), or ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activity. RNA-sequencing was used to identify potential differences in post-photosynthetic metabolism that would influence δ13C; however, no correlations were identified that would indicate significant differences in post-photosynthetic fractionation between lines. Variation in δ13C has been observed between C4 subtypes, but differential expression of NADP-ME and PEP-CK pathways within these lines did not correlate with δ13C. However, co-expression network analysis provided novel evidence for isoforms of C4 enzymes and putative transporters. Together, these data indicate that diversity in maize δ13C cannot be fully explained by variation in CA, PEPC, or Rubisco activity or gene expression. The findings further emphasise the need for future work exploring the influence of stomatal sensitivity and mesophyll conductance on δ13C in maize.
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Affiliation(s)
- Allison R Kolbe
- School of Biological Sciences, PO Box 644236, Washington State University, Pullman, WA 99164, USA
| | - Anthony J Studer
- Department of Crop Sciences, 1201 West Gregory Drive, Edward R. Madigan Laboratory 289, University of Illinois Urbana-Champaign, Urbana, IL 61801, USA
| | - Asaph B Cousins
- School of Biological Sciences, PO Box 644236, Washington State University, Pullman, WA 99164, USA
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20
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Ubierna N, Gandin A, Cousins AB. The response of mesophyll conductance to short-term variation in CO2 in the C4 plants Setaria viridis and Zea mays. JOURNAL OF EXPERIMENTAL BOTANY 2018; 69:1159-1170. [PMID: 29474683 PMCID: PMC6018935 DOI: 10.1093/jxb/erx464] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/26/2017] [Accepted: 01/10/2018] [Indexed: 05/13/2023]
Abstract
Mesophyll conductance (gm) limits rates of C3 photosynthesis but little is known about its role in C4 photosynthesis. If gm were to limit C4 photosynthesis, it would likely be at low CO2 concentrations (pCO2). However, data on C4-gm across ranges of pCO2 are scarce. We describe the response of C4-gm to short-term variation in pCO2, at three temperatures in Setaria viridis, and at 25 °C in Zea mays. Additionally, we quantified the effect of finite gm calculations of leakiness (ϕ) and the potential limitations to photosynthesis imposed by stomata, mesophyll, and carbonic anhydrase (CA) across pCO2. In both species, gm increased with decreasing pCO2. Including a finite gm resulted in either no change or increased ϕ compared with values calculated with infinite gm depending on whether the observed 13C discrimination was high (Setaria) or low (Zea). Post-transitional regulation of the maximal PEP carboxylation rate and PEP regeneration limitation could influence estimates of gm and ϕ. At pCO2 below ambient, the photosynthetic rate was limited by CO2 availability. In this case, the limitation imposed by the mesophyll was similar or slightly lower than stomata limitation. At very low pCO2, CA further constrained photosynthesis. High gm could increase CO2 assimilation at low pCO2 and improve photosynthetic efficiency under situations when CO2 is limited, such as drought.
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Affiliation(s)
- Nerea Ubierna
- School of Biological Sciences, Molecular Plant Sciences, Washington State University, Pullman, Washington, USA
| | - Anthony Gandin
- School of Biological Sciences, Molecular Plant Sciences, Washington State University, Pullman, Washington, USA
| | - Asaph B Cousins
- School of Biological Sciences, Molecular Plant Sciences, Washington State University, Pullman, Washington, USA
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21
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Ubierna N, Holloway-Phillips MM, Farquhar GD. Using Stable Carbon Isotopes to Study C 3 and C 4 Photosynthesis: Models and Calculations. Methods Mol Biol 2018; 1770:155-196. [PMID: 29978402 DOI: 10.1007/978-1-4939-7786-4_10] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Stable carbon isotopes are a powerful tool to study photosynthesis. Initial applications consisted of determining isotope ratios of plant biomass using mass spectrometry. Subsequently, theoretical models relating C-isotope values to gas exchange characteristics were introduced and tested against instantaneous online measurements of 13C photosynthetic discrimination. Beginning in the twenty-first century, tunable diode laser spectroscopes with sufficient precision for determining isotope mixing ratios became commercially available. This has allowed collection of large data sets, at low cost and with unprecedented temporal resolution. With more data and accompanying knowledge, it has become apparent that there is a need for increased complexity in models and calculations. This chapter describes instantaneous online measurements of 13C photosynthetic discrimination, provides recommendations for experimental setup, and presents a thorough compilation of equations needed for different applications.
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Affiliation(s)
- Nerea Ubierna
- School of Biological Sciences, Molecular Plant Sciences, Washington State University, Pullman, WA, USA.
| | | | - Graham D Farquhar
- Research School of Biology, Australian National University, Canberra, ACT, Australia
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22
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Zhang S, Tang S, Tang C, Luo M, Jia G, Zhi H, Diao X. SiSTL2 Is Required for Cell Cycle, Leaf Organ Development, Chloroplast Biogenesis, and Has Effects on C 4 Photosynthesis in Setaria italica (L.) P. Beauv. FRONTIERS IN PLANT SCIENCE 2018; 9:1103. [PMID: 30105043 PMCID: PMC6077218 DOI: 10.3389/fpls.2018.01103] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/26/2018] [Accepted: 07/09/2018] [Indexed: 05/20/2023]
Abstract
Deoxycytidine monophosphate deaminase (DCD) is a key enzyme in the de novo dTTP biosynthesis pathway. Previous studies have indicated that DCD plays key roles in the maintenance of the balance of dNTP pools, cell cycle progression, and plant development. However, few studies have elucidated the functions of the DCD gene in Panicoideae plants. Setaria has been proposed as an ideal model of Panicoideae grasses, especially for C4 photosynthesis research. Here, a Setaria italica stripe leaf mutant (sistl2) was isolated from EMS-induced lines of "Yugu1," the wild-type parent. The sistl2 mutant exhibited semi-dwarf, striped leaves, abnormal chloroplast ultrastructure, and delayed cell cycle progression compared with Yugu1. High-throughput sequencing and map-based cloning identified the causal gene SiSTL2, which encodes a DCD protein. The occurrence of a single-base G to A substitution in the fifth intron introduced alternative splicing, which led to the early termination of translation. Further physiological and transcriptomic investigation indicated that SiSTL2 plays an essential role in the regulation of chloroplast biogenesis, cell cycle, and DNA replication, which suggested that the gene has conserved functions in both foxtail millet and rice. Remarkably, in contrast to DCD mutants in C3 rice, sistl2 showed a significant reduction in leaf cell size and affected C4 photosynthetic capacity in foxtail millet. qPCR showed that SiSTL2 had a similar expression pattern to typical C4 genes in response to a low CO2 environment. Moreover, the loss of function of SiSTL2 resulted in a reduction of leaf 13C content and the enrichment of DEGs in photosynthetic carbon fixation. Our research provides in-depth knowledge of the role of DCD in the C4 photosynthesis model S. italica and proposed new directions for further study of the function of DCD.
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Affiliation(s)
- Shuo Zhang
- These authors have contributed equally to this work
| | - Sha Tang
- These authors have contributed equally to this work
| | | | | | | | - Hui Zhi
- *Correspondence: Hui Zhi, Xianmin Diao,
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23
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Sonawane BV, Sharwood RE, von Caemmerer S, Whitney SM, Ghannoum O. Short-term thermal photosynthetic responses of C4 grasses are independent of the biochemical subtype. JOURNAL OF EXPERIMENTAL BOTANY 2017; 68:5583-5597. [PMID: 29045727 PMCID: PMC5853683 DOI: 10.1093/jxb/erx350] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/27/2017] [Accepted: 09/14/2017] [Indexed: 05/20/2023]
Abstract
C4 photosynthesis evolved independently many times, resulting in multiple biochemical pathways; however, little is known about how these different pathways respond to temperature. We investigated the photosynthetic responses of eight C4 grasses belonging to three biochemical subtypes (NADP-ME, PEP-CK, and NAD-ME) to four leaf temperatures (18, 25, 32, and 40 °C). We also explored whether the biochemical subtype influences the thermal responses of (i) in vitro PEPC (Vpmax) and Rubisco (Vcmax) maximal activities, (ii) initial slope (IS) and CO2-saturated rate (CSR) derived from the A-Ci curves, and (iii) CO2 leakage out of the bundle sheath estimated from carbon isotope discrimination. We focussed on leakiness and the two carboxylases because they determine the coordination of the CO2-concentrating mechanism and are important for parameterizing the semi-mechanistic C4 photosynthesis model. We found that the thermal responses of Vpmax and Vcmax, IS, CSR, and leakiness varied among the C4 species independently of the biochemical subtype. No correlation was observed between Vpmax and IS or between Vcmax and CSR; while the ratios Vpmax/Vcmax and IS/CSR did not correlate with leakiness among the C4 grasses. Determining mesophyll and bundle sheath conductances in diverse C4 grasses is required to further elucidate how C4 photosynthesis responds to temperature.
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Affiliation(s)
- Balasaheb V Sonawane
- ARC Centre of Excellence for Translational Photosynthesis and Hawkesbury Institute for the Environment, Western Sydney University, Richmond NSW, Australia
| | - Robert E Sharwood
- ARC Centre of Excellence for Translational Photosynthesis and Research School of Biology, Australian National University, Canberra ACT, Australia
| | - Susanne von Caemmerer
- ARC Centre of Excellence for Translational Photosynthesis and Research School of Biology, Australian National University, Canberra ACT, Australia
| | - Spencer M Whitney
- ARC Centre of Excellence for Translational Photosynthesis and Research School of Biology, Australian National University, Canberra ACT, Australia
| | - Oula Ghannoum
- ARC Centre of Excellence for Translational Photosynthesis and Hawkesbury Institute for the Environment, Western Sydney University, Richmond NSW, Australia
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24
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Liang MC, Mahata S, Laskar AH, Thiemens MH, Newman S. Oxygen isotope anomaly in tropospheric CO 2 and implications for CO 2 residence time in the atmosphere and gross primary productivity. Sci Rep 2017; 7:13180. [PMID: 29030617 PMCID: PMC5640618 DOI: 10.1038/s41598-017-12774-w] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2017] [Accepted: 09/15/2017] [Indexed: 11/09/2022] Open
Abstract
The abundance variations of near surface atmospheric CO2 isotopologues (primarily 16O12C16O, 16O13C16O, 17O12C16O, and 18O12C16O) represent an integrated signal from anthropogenic/biogeochemical processes, including fossil fuel burning, biospheric photosynthesis and respiration, hydrospheric isotope exchange with water, and stratospheric photochemistry. Oxygen isotopes, in particular, are affected by the carbon and water cycles. Being a useful tracer that directly probes governing processes in CO2 biogeochemical cycles, Δ17O (=ln(1 + δ17O) - 0.516 × ln(1 + δ18O)) provides an alternative constraint on the strengths of the associated cycles involving CO2. Here, we analyze Δ17O data from four places (Taipei, Taiwan; South China Sea; La Jolla, United States; Jerusalem, Israel) in the northern hemisphere (with a total of 455 measurements) and find a rather narrow range (0.326 ± 0.005‰). A conservative estimate places a lower limit of 345 ± 70 PgC year-1 on the cycling flux between the terrestrial biosphere and atmosphere and infers a residence time of CO2 of 1.9 ± 0.3 years (upper limit) in the atmosphere. A Monte Carlo simulation that takes various plant uptake scenarios into account yields a terrestrial gross primary productivity of 120 ± 30 PgC year-1 and soil invasion of 110 ± 30 PgC year-1, providing a quantitative assessment utilizing the oxygen isotope anomaly for quantifying CO2 cycling.
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Affiliation(s)
- Mao-Chang Liang
- Research Center for Environmental Changes, Academia Sinica, Taipei, Taiwan. .,Graduate Institute of Astronomy, National Central University, Taoyuan, Taiwan.
| | - Sasadhar Mahata
- Research Center for Environmental Changes, Academia Sinica, Taipei, Taiwan
| | - Amzad H Laskar
- Research Center for Environmental Changes, Academia Sinica, Taipei, Taiwan
| | - Mark H Thiemens
- Department of Chemistry and Biochemistry, University of California at San Diego, La Jolla, USA
| | - Sally Newman
- Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, USA
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Ubierna N, Gandin A, Boyd RA, Cousins AB. Temperature response of mesophyll conductance in three C 4 species calculated with two methods: 18 O discrimination and in vitro V pmax. THE NEW PHYTOLOGIST 2017; 214:66-80. [PMID: 27918624 DOI: 10.1111/nph.14359] [Citation(s) in RCA: 42] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/19/2016] [Accepted: 10/27/2016] [Indexed: 05/08/2023]
Abstract
Mesophyll conductance (gm ) is an important factor limiting rates of C3 photosynthesis. However, its role in C4 photosynthesis is poorly understood because it has been historically difficult to estimate. We use two methods to derive the temperature responses of gm in C4 species. The first (Δ18 O) combines measurements of gas exchange with models and measurements of 18 O discrimination. The second method (in vitro Vpmax ) derives gm by retrofitting models of C4 photosynthesis and 13 C discrimination with gas exchange, kinetic constants and in vitro Vpmax measurements. The two methods produced similar gm for Setaria viridis and Zea mays. Additionally, we present the first temperature response (10-40°C) of C4 gm in S. viridis, Z. mays and Miscanthus × giganteus. Values for gm at 25°C ranged from 2.90 to 7.85 μmol m-2 s-1 Pa-1 . Our study demonstrated that: the two described methods are suitable to calculate gm in C4 species; gm values in C4 are similar to high-end values reported for C3 species; and gm increases with temperature analogous to reports for C3 species and the response is species specific. These results improve our mechanistic understanding of C4 photosynthesis.
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Affiliation(s)
- Nerea Ubierna
- School of Biological Sciences, Molecular Plant Sciences, Washington State University, Pullman, WA, 99164-4236, USA
| | - Anthony Gandin
- School of Biological Sciences, Molecular Plant Sciences, Washington State University, Pullman, WA, 99164-4236, USA
| | - Ryan A Boyd
- School of Biological Sciences, Molecular Plant Sciences, Washington State University, Pullman, WA, 99164-4236, USA
| | - Asaph B Cousins
- School of Biological Sciences, Molecular Plant Sciences, Washington State University, Pullman, WA, 99164-4236, USA
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26
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DiMario RJ, Clayton H, Mukherjee A, Ludwig M, Moroney JV. Plant Carbonic Anhydrases: Structures, Locations, Evolution, and Physiological Roles. MOLECULAR PLANT 2017; 10:30-46. [PMID: 27646307 PMCID: PMC5226100 DOI: 10.1016/j.molp.2016.09.001] [Citation(s) in RCA: 124] [Impact Index Per Article: 17.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/25/2016] [Revised: 08/30/2016] [Accepted: 09/04/2016] [Indexed: 05/19/2023]
Abstract
Carbonic anhydrases (CAs) are zinc metalloenzymes that catalyze the interconversion of CO2 and HCO3- and are ubiquitous in nature. Higher plants contain three evolutionarily distinct CA families, αCAs, βCAs, and γCAs, where each family is represented by multiple isoforms in all species. Alternative splicing of CA transcripts appears common; consequently, the number of functional CA isoforms in a species may exceed the number of genes. CAs are expressed in numerous plant tissues and in different cellular locations. The most prevalent CAs are those in the chloroplast, cytosol, and mitochondria. This diversity in location is paralleled in the many physiological and biochemical roles that CAs play in plants. In this review, the number and types of CAs in C3, C4, and crassulacean acid metabolism (CAM) plants are considered, and the roles of the α and γCAs are briefly discussed. The remainder of the review focuses on plant βCAs and includes the identification of homologs between species using phylogenetic approaches, a consideration of the inter- and intracellular localization of the proteins, along with the evidence for alternative splice forms. Current understanding of βCA tissue-specific expression patterns and what controls them are reviewed, and the physiological roles for which βCAs have been implicated are presented.
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Affiliation(s)
- Robert J DiMario
- Department of Biological Sciences, Louisiana State University, Baton Rouge, LA 70803, USA
| | - Harmony Clayton
- School of Chemistry and Biochemistry, University of Western Australia, Perth, WA 6009 Australia
| | - Ananya Mukherjee
- Department of Biological Sciences, Louisiana State University, Baton Rouge, LA 70803, USA
| | - Martha Ludwig
- School of Chemistry and Biochemistry, University of Western Australia, Perth, WA 6009 Australia
| | - James V Moroney
- Department of Biological Sciences, Louisiana State University, Baton Rouge, LA 70803, USA.
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27
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Moinuddin M, Gulzar S, Hameed A, Gul B, Ajmal Khan M, Edwards GE. Differences in photosynthetic syndromes of four halophytic marsh grasses in Pakistan. PHOTOSYNTHESIS RESEARCH 2017; 131:51-64. [PMID: 27450569 DOI: 10.1007/s11120-016-0296-0] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/11/2016] [Accepted: 07/11/2016] [Indexed: 06/06/2023]
Abstract
Salt-tolerant grasses of warm sub-tropical ecosystems differ in their distribution patterns with respect to salinity and moisture regimes. Experiments were conducted on CO2 fixation and light harvesting processes of four halophytic C4 grasses grown under different levels of salinity (0, 200 and 400 mM NaCl) under ambient environmental conditions. Two species were from a high saline coastal marsh (Aeluropus lagopoides and Sporobolus tremulus) and two were from a moderate saline sub-coastal draw-down tidal marsh (Paspalum paspalodes and Paspalidium geminatum). Analyses of the carbon isotope ratios of leaf biomass in plants indicated that carbon assimilation was occurring by C4 photosynthesis in all species during growth under varying levels of salinity. In the coastal species, with increasing salinity, there was a parallel decrease in rates of CO2 fixation (A), transpiration (E) and stomatal conductance (g s), with no effect on water use efficiency (WUE). These species were adapted for photoprotection by an increase in the Mehler reaction with an increase in activity of PSII/CO2 fixed accompanied by high levels of antioxidant enzymes, superoxide dismutase and ascorbate peroxidase. The sub-coastal species P. paspalodes and P. geminatum had high levels of carotenoid pigments and non-photochemical quenching by the xanthophyll cycle.
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Affiliation(s)
- Muhammad Moinuddin
- Institute of Sustainable Halophyte Utilization, University of Karachi, Karachi, 75270, Pakistan
| | - Salman Gulzar
- Institute of Sustainable Halophyte Utilization, University of Karachi, Karachi, 75270, Pakistan
| | - Abdul Hameed
- Institute of Sustainable Halophyte Utilization, University of Karachi, Karachi, 75270, Pakistan
| | - Bilquees Gul
- Institute of Sustainable Halophyte Utilization, University of Karachi, Karachi, 75270, Pakistan
| | - M Ajmal Khan
- Institute of Sustainable Halophyte Utilization, University of Karachi, Karachi, 75270, Pakistan
| | - Gerald E Edwards
- School of Biological Sciences, Washington State University, Pullman, WA, 99164-4236, USA.
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28
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Ma JY, Sun W, Koteyeva NK, Voznesenskaya E, Stutz SS, Gandin A, Smith-Moritz AM, Heazlewood JL, Cousins AB. Influence of light and nitrogen on the photosynthetic efficiency in the C 4 plant Miscanthus × giganteus. PHOTOSYNTHESIS RESEARCH 2017; 131:1-13. [PMID: 27531584 DOI: 10.1007/s11120-016-0281-7] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/05/2015] [Accepted: 05/26/2016] [Indexed: 06/06/2023]
Abstract
There are numerous studies describing how growth conditions influence the efficiency of C4 photosynthesis. However, it remains unclear how changes in the biochemical capacity versus leaf anatomy drives this acclimation. Therefore, the aim of this study was to determine how growth light and nitrogen availability influence leaf anatomy, biochemistry and the efficiency of the CO2 concentrating mechanism in Miscanthus × giganteus. There was an increase in the mesophyll cell wall surface area but not cell well thickness in the high-light (HL) compared to the low-light (LL) grown plants suggesting a higher mesophyll conductance in the HL plants, which also had greater photosynthetic capacity. Additionally, the HL plants had greater surface area and thickness of bundle-sheath cell walls compared to LL plants, suggesting limited differences in bundle-sheath CO2 conductance because the increased area was offset by thicker cell walls. The gas exchange estimates of phosphoenolpyruvate carboxylase (PEPc) activity were significantly less than the in vitro PEPc activity, suggesting limited substrate availability in the leaf due to low mesophyll CO2 conductance. Finally, leakiness was similar across all growth conditions and generally did not change under the different measurement light conditions. However, differences in the stable isotope composition of leaf material did not correlate with leakiness indicating that dry matter isotope measurements are not a good proxy for leakiness. Taken together, these data suggest that the CO2 concentrating mechanism in Miscanthus is robust under low-light and limited nitrogen growth conditions, and that the observed changes in leaf anatomy and biochemistry likely help to maintain this efficiency.
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Affiliation(s)
- Jian-Ying Ma
- Key Laboratory of Biogeography and Bioresource in Arid Land, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Urumqi, 830011, China
- School of Biological Science, Washington State University, Pullman, WA, 99163, USA
| | - Wei Sun
- School of Biological Science, Washington State University, Pullman, WA, 99163, USA
- Institute of Grassland Science, Key Laboratory of Vegetation Ecology, Ministry of Education, Northeast Normal University, Changchun, 130024, China
| | - Nuria K Koteyeva
- Laboratory of Anatomy and Morphology, V.L. Komarov Botanical Institute of the Russian Academy of Sciences, St. Petersburg, Russia
| | - Elena Voznesenskaya
- Laboratory of Anatomy and Morphology, V.L. Komarov Botanical Institute of the Russian Academy of Sciences, St. Petersburg, Russia
| | - Samantha S Stutz
- School of Biological Science, Washington State University, Pullman, WA, 99163, USA
| | - Anthony Gandin
- School of Biological Science, Washington State University, Pullman, WA, 99163, USA
| | - Andreia M Smith-Moritz
- Joint BioEnergy Institute and Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA
| | - Joshua L Heazlewood
- Joint BioEnergy Institute and Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA
- ARC Centre of Excellence in Plant Cell Walls, School of BioSciences, The University of Melbourne, Melbourne, VIC, 3010, Australia
| | - Asaph B Cousins
- School of Biological Science, Washington State University, Pullman, WA, 99163, USA.
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29
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Wang S, Tholen D, Zhu X. C 4 photosynthesis in C 3 rice: a theoretical analysis of biochemical and anatomical factors. PLANT, CELL & ENVIRONMENT 2017; 40:80-94. [PMID: 27628301 PMCID: PMC6139432 DOI: 10.1111/pce.12834] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/09/2016] [Revised: 09/08/2016] [Accepted: 09/10/2016] [Indexed: 05/05/2023]
Abstract
Engineering C4 photosynthesis into rice has been considered a promising strategy to increase photosynthesis and yield. A question that remains to be answered is whether expressing a C4 metabolic cycle into a C3 leaf structure and without removing the C3 background metabolism improves photosynthetic efficiency. To explore this question, we developed a 3D reaction diffusion model of bundle-sheath and connected mesophyll cells in a C3 rice leaf. Our results show that integrating a C4 metabolic pathway into rice leaves with a C3 metabolism and mesophyll structure may lead to an improved photosynthesis under current ambient CO2 concentration. We analysed a number of physiological factors that influence the CO2 uptake rate, which include the chloroplast surface area exposed to intercellular air space, bundle-sheath cell wall thickness, bundle-sheath chloroplast envelope permeability, Rubisco concentration and the energy partitioning between C3 and C4 cycles. Among these, partitioning of energy between C3 and C4 photosynthesis and the partitioning of Rubisco between mesophyll and bundle-sheath cells are decisive factors controlling photosynthetic efficiency in an engineered C3 -C4 leaf. The implications of the results for the sequence of C4 evolution are also discussed.
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Affiliation(s)
- Shuyue Wang
- Key Laboratory of Computational Biology, CAS‐MPG Partner Institute for Computational Biology, Shanghai Institutes for Biological SciencesChinese Academy of SciencesShanghai200031China
- University of Chinese Academy of SciencesBeijing100049China
| | - Danny Tholen
- Institute of Botany, Department of Integrative BiologyUniversity of Natural Resources and Applied Life Sciences, BOKU ViennaGregor‐Mendel‐Str. 33A‐1180ViennaAustria
| | - Xin‐Guang Zhu
- Key Laboratory of Computational Biology, CAS‐MPG Partner Institute for Computational Biology, Shanghai Institutes for Biological SciencesChinese Academy of SciencesShanghai200031China
- University of Chinese Academy of SciencesBeijing100049China
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30
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Osborn HL, Alonso-Cantabrana H, Sharwood RE, Covshoff S, Evans JR, Furbank RT, von Caemmerer S. Effects of reduced carbonic anhydrase activity on CO2 assimilation rates in Setaria viridis: a transgenic analysis. JOURNAL OF EXPERIMENTAL BOTANY 2017; 68:299-310. [PMID: 27702996 PMCID: PMC5853810 DOI: 10.1093/jxb/erw357] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/19/2016] [Accepted: 09/05/2016] [Indexed: 05/22/2023]
Abstract
In C4 species, the major β-carbonic anhydrase (β-CA) localized in the mesophyll cytosol catalyses the hydration of CO2 to HCO3-, which phosphoenolpyruvate carboxylase uses in the first step of C4 photosynthesis. To address the role of CA in C4 photosynthesis, 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 CO2 partial pressure (pCO2). At low pCO2, a strong correlation between CO2 assimilation rates and CA hydration rates was observed. C18O16O isotope discrimination was used to estimate the mesophyll conductance to CO2 diffusion 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 CO2 assimilation rate to cytosolic pCO2 (ACm) and cytosolic CA activity. However, the relationship between the initial slope of the response of CO2 assimilation 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 CO2 assimilation rates at low pCO2.
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Affiliation(s)
- Hannah L Osborn
- 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-Cantabrana
- 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
| | - Robert E Sharwood
- 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
| | - Sarah Covshoff
- Department of Plant Sciences, University of Cambridge, Cambridge CB2 3EA, UK
| | - John R Evans
- 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
| | - Robert T Furbank
- 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
| | - Susanne von Caemmerer
- 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
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31
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Gong XY, Schäufele R, Schnyder H. Bundle-sheath leakiness and intrinsic water use efficiency of a perennial C4 grass are increased at high vapour pressure deficit during growth. JOURNAL OF EXPERIMENTAL BOTANY 2017; 68:321-333. [PMID: 27864539 PMCID: PMC5853292 DOI: 10.1093/jxb/erw417] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/27/2016] [Accepted: 10/20/2016] [Indexed: 05/05/2023]
Abstract
Bundle-sheath leakiness (ϕ) is a key parameter of the CO2-concentrating mechanism of C4 photosynthesis and is related to leaf-level intrinsic water use efficiency (WUEi). This work studied short-term dynamic responses of ϕ to alterations of atmospheric CO2 concentration in Cleistogenes squarrosa, a perennial grass, grown at high (1.6 kPa) or low (0.6 kPa) vapour pressure deficit (VPD) combined with high or low N supply in controlled environment experiments. ϕ was determined by concurrent measurements of photosynthetic gas exchange and on-line carbon isotope discrimination, using a new protocol. Growth at high VPD led to an increase of ϕ by 0.13 and a concurrent increase of WUEi by 14%, with similar effects at both N levels. ϕ responded dynamically to intercellular CO2 concentration (C i), increasing with C i Across treatments, ϕ was negatively correlated to the ratio of CO2 saturated assimilation rate to carboxylation efficiency (a proxy of the relative activities of Rubisco and phosphoenolpyruvate carboxylase) indicating that the long-term environmental effect on ϕ was related to the balance between C3 and C4 cycles. Our study revealed considerable dynamic and long-term variation in ϕ of C. squarrosa, suggesting that ϕ should be determined when carbon isotope discrimination is used to assess WUEi Also, the data indicate a trade-off between WUEi and energetic efficiency in C. squarrosa.
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Affiliation(s)
- Xiao Ying Gong
- Lehrstuhl für Grünlandlehre, Technische Universität München, Alte Akademie 12, 85354 Freising, Germany
| | - Rudi Schäufele
- Lehrstuhl für Grünlandlehre, Technische Universität München, Alte Akademie 12, 85354 Freising, Germany
| | - Hans Schnyder
- Lehrstuhl für Grünlandlehre, Technische Universität München, Alte Akademie 12, 85354 Freising, Germany
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Studer AJ, Schnable JC, Weissmann S, Kolbe AR, McKain MR, Shao Y, Cousins AB, Kellogg EA, Brutnell TP. The draft genome of the C 3 panicoid grass species Dichanthelium oligosanthes. Genome Biol 2016; 17:223. [PMID: 27793170 PMCID: PMC5084476 DOI: 10.1186/s13059-016-1080-3] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2015] [Accepted: 10/05/2016] [Indexed: 01/08/2023] Open
Abstract
BACKGROUND Comparisons between C3 and C4 grasses often utilize C3 species from the subfamilies Ehrhartoideae or Pooideae and C4 species from the subfamily Panicoideae, two clades that diverged over 50 million years ago. The divergence of the C3 panicoid grass Dichanthelium oligosanthes from the independent C4 lineages represented by Setaria viridis and Sorghum bicolor occurred approximately 15 million years ago, which is significantly more recent than members of the Bambusoideae, Ehrhartoideae, and Pooideae subfamilies. D. oligosanthes is ideally placed within the panicoid clade for comparative studies of C3 and C4 grasses. RESULTS We report the assembly of the nuclear and chloroplast genomes of D. oligosanthes, from high-throughput short read sequencing data and a comparative transcriptomics analysis of the developing leaf of D. oligosanthes, S. viridis, and S. bicolor. Physiological and anatomical characterizations verified that D. oligosanthes utilizes the C3 pathway for carbon fixation and lacks Kranz anatomy. Expression profiles of transcription factors along developing leaves of D. oligosanthes and S. viridis were compared with previously published data from S. bicolor, Zea mays, and Oryza sativa to identify a small suite of transcription factors that likely acquired functions specifically related to C4 photosynthesis. CONCLUSIONS The phylogenetic location of D. oligosanthes makes it an ideal C3 plant for comparative analysis of C4 evolution in the panicoid grasses. This genome will not only provide a better C3 species for comparisons with C4 panicoid grasses, but also highlights the power of using high-throughput sequencing to address questions in evolutionary biology.
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Affiliation(s)
- Anthony J. Studer
- Donald Danforth Plant Science Center, St. Louis, MO 63132 USA
- Present address: Department of Crop Sciences, University of Illinois Urbana-Champaign, Urbana, IL 61801 USA
| | - James C. Schnable
- Donald Danforth Plant Science Center, St. Louis, MO 63132 USA
- Present address: Department of Agronomy and Horticulture, University of Nebraska-Lincoln, Lincoln, NE 68588 USA
| | - Sarit Weissmann
- Donald Danforth Plant Science Center, St. Louis, MO 63132 USA
| | - Allison R. Kolbe
- School of Biological Sciences, Washington State University, Pullman, WA 99164 USA
| | | | - Ying Shao
- Donald Danforth Plant Science Center, St. Louis, MO 63132 USA
- St. Jude Children’s Research Hospital, Pediatric Cancer Genome Project, Memphis, TN USA
| | - Asaph B. Cousins
- School of Biological Sciences, Washington State University, Pullman, WA 99164 USA
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33
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Lightfoot E, Przelomska N, Craven M, O Connell TC, He L, Hunt HV, Jones MK. Intraspecific carbon and nitrogen isotopic variability in foxtail millet (Setaria italica). RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2016; 30:1475-1487. [PMID: 27321835 DOI: 10.1002/rcm.7583] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/23/2016] [Revised: 04/06/2016] [Accepted: 04/07/2016] [Indexed: 06/06/2023]
Abstract
RATIONALE Isotopic palaeodietary studies generally focus on bone collagen from human and/or animal remains. While plant remains are rarely analysed, it is known that plant isotope values can vary as a result of numerous factors, including soil conditions, the environment and type of plant. The millets were important food crops in prehistoric Eurasia, yet little is known about the isotopic differences within millet species. METHODS Here we compare the stable isotope ratios within and between Setaria italica plants grown in a controlled environment chamber. Using homogenised samples, we compare carbon isotope ratios of leaves and grains, and nitrogen isotope ratios of grains, from 29 accessions of Setaria italica. RESULTS We find significant isotopic variability within single leaves and panicles, and between leaves and panicles within the same plant, which must be considered when undertaking plant isotope studies. We find that the leaves and grains from the different accessions have a ca 2‰ range in δ(13) C values, while the nitrogen isotope values in the grains have a ca 6‰ range. We also find an average offset of 0.9‰ between leaves and grains in their δ(13) C values. CONCLUSIONS The variation found is large enough to have archaeological implications and within- and between-plant isotope variability should be considered in isotope studies. The range in δ(15) N values is particularly significant as it is larger than the typical values quoted for a trophic level enrichment, and as such may lead to erroneous interpretations of the amount of animal protein in human or animal diets. It is therefore necessary to account for the variability in plant stable isotope values during palaeodietary reconstructions. Copyright © 2016 John Wiley & Sons, Ltd.
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Affiliation(s)
- Emma Lightfoot
- McDonald Institute for Archaeological Research, University of Cambridge, Downing Street, Cambridge, CB2 3ER, UK
| | - Natalia Przelomska
- Department of Archaeology and Anthropology, University of Cambridge, Downing Street, Cambridge, CB2 3DZ, UK
| | - Martha Craven
- Department of Archaeology and Anthropology, University of Cambridge, Downing Street, Cambridge, CB2 3DZ, UK
| | - Tamsin C O Connell
- Department of Archaeology and Anthropology, University of Cambridge, Downing Street, Cambridge, CB2 3DZ, UK
| | - Lu He
- College of Agriculture, Shanxi Agricultural University, Taigu, 030801, China
| | - Harriet V Hunt
- McDonald Institute for Archaeological Research, University of Cambridge, Downing Street, Cambridge, CB2 3ER, UK
| | - Martin K Jones
- Department of Archaeology and Anthropology, University of Cambridge, Downing Street, Cambridge, CB2 3DZ, UK
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34
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Ellsworth PZ, Cousins AB. Carbon isotopes and water use efficiency in C4 plants. CURRENT OPINION IN PLANT BIOLOGY 2016; 31:155-61. [PMID: 27155062 DOI: 10.1016/j.pbi.2016.04.006] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/10/2016] [Revised: 04/07/2016] [Accepted: 04/14/2016] [Indexed: 05/13/2023]
Abstract
Drought is a major agricultural problem worldwide. Therefore, selection for increased water use efficiency (WUE) in food and biofuel crop species will be an important trait in plant breeding programs. The leaf carbon isotopic composition (δ(13)Cleaf) has been suggested to serve as a rapid and effective high throughput phenotyping method for WUE in both C3 and C4 species. This is because WUE, leaf carbon discrimination (Δ(13)Cleaf), and δ(13)Cleaf are correlated through their relationships with intercellular to ambient CO2 partial pressures (Ci/Ca). However, in C4 plants, changing environmental conditions may influence photosynthetic efficiency (bundle-sheath leakiness) and post-photosynthetic fractionation that will potentially alter the relationship between δ(13)Cleaf and Ci/Ca. Here we discuss how these factors influence the relationship between δ(13)Cleaf and WUE, and the potential of using δ(13)Cleaf as a meaningful proxy for WUE.
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Affiliation(s)
| | - Asaph B Cousins
- Washington State University, Pullman, WA 99163, United States.
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35
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Ludwig M. Evolution of carbonic anhydrase in C4 plants. CURRENT OPINION IN PLANT BIOLOGY 2016; 31:16-22. [PMID: 27016649 DOI: 10.1016/j.pbi.2016.03.003] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/22/2015] [Revised: 02/26/2016] [Accepted: 03/03/2016] [Indexed: 06/05/2023]
Abstract
During the evolution of C4 photosynthesis, the intracellular location with most carbonic anhydrase (CA) activity has changed. In Flaveria, the loss of the sequence encoding a chloroplast transit peptide from an ancestral C3 CA ortholog confined the C4 isoform to the mesophyll cell cytosol. Recent studies indicate that sequence elements and histone modifications controlling the expression of C4-associated CAs were likely present in the C3 ancestral chromatin, enabling the evolution of the C4 pathway. Almost complete abolishment of maize CA activity yields no obvious phenotype at ambient CO2 levels. This contrasts with results for Flaveria CA mutants, and has opened discussion on the role of CA in the C4 carbon concentrating mechanism.
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Affiliation(s)
- Martha Ludwig
- School of Chemistry and Biochemistry [310], University of Western Australia, 35 Stirling Highway, Crawley, Western Australia 6009, Australia.
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Barbour MM, Evans JR, Simonin KA, von Caemmerer S. Online CO2 and H2 O oxygen isotope fractionation allows estimation of mesophyll conductance in C4 plants, and reveals that mesophyll conductance decreases as leaves age in both C4 and C3 plants. THE NEW PHYTOLOGIST 2016; 210:875-89. [PMID: 26778088 DOI: 10.1111/nph.13830] [Citation(s) in RCA: 73] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/21/2015] [Accepted: 11/30/2015] [Indexed: 05/09/2023]
Abstract
Mesophyll conductance significantly, and variably, limits photosynthesis but we currently have no reliable method of measurement for C4 plants. An online oxygen isotope technique was developed to allow quantification of mesophyll conductance in C4 plants and to provide an alternative estimate in C3 plants. The technique is compared to an established carbon isotope method in three C3 species. Mesophyll conductance of C4 species was similar to that in the C3 species measured, and declined in both C4 and C3 species as leaves aged from fully expanded to senescing. In cotton leaves, simultaneous measurement of carbon and oxygen isotope discrimination allowed the partitioning of total conductance to the chloroplasts into cell wall and plasma membrane versus chloroplast membrane components, if CO2 was assumed to be isotopically equilibrated with cytosolic water, and the partitioning remained stable with leaf age. The oxygen isotope technique allowed estimation of mesophyll conductance in C4 plants and, when combined with well-established carbon isotope techniques, may provide additional information on mesophyll conductance in C3 plants.
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Affiliation(s)
- Margaret M Barbour
- Faculty of Agriculture and Environment, The University of Sydney, Private Bag 4011, Narellan, NSW, 2567, Australia
| | - John R Evans
- Research School of Biology, The Australian National University, Acton, ACT, 0200, Australia
| | - Kevin A Simonin
- Department of Biology, San Francisco State University, San Francisco, CA, 94132, USA
| | - Susanne von Caemmerer
- Research School of Biology, The Australian National University, Acton, ACT, 0200, Australia
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Alonso-Cantabrana H, von Caemmerer S. Carbon isotope discrimination as a diagnostic tool for C4 photosynthesis in C3-C4 intermediate species. JOURNAL OF EXPERIMENTAL BOTANY 2016; 67:3109-21. [PMID: 26862154 PMCID: PMC4867892 DOI: 10.1093/jxb/erv555] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
The presence and activity of the C4 cycle in C3-C4 intermediate species have proven difficult to analyze, especially when such activity is low. This study proposes a strategy to detect C4 activity and estimate its contribution to overall photosynthesis in intermediate plants, by using tunable diode laser absorption spectroscopy (TDLAS) coupled to gas exchange systems to simultaneously measure the CO2 responses of CO2 assimilation (A) and carbon isotope discrimination (Δ) under low O2 partial pressure. Mathematical models of C3-C4 photosynthesis and Δ are then fitted concurrently to both responses using the same set of constants. This strategy was applied to the intermediate species Flaveria floridana and F. brownii, and to F. pringlei and F. bidentis as C3 and C4 controls, respectively. Our results support the presence of a functional C4 cycle in F. floridana, that can fix 12-21% of carbon. In F. brownii, 75-100% of carbon is fixed via the C4 cycle, and the contribution of mesophyll Rubisco to overall carbon assimilation increases with CO2 partial pressure in both intermediate plants. Combined gas exchange and Δ measurement and modeling is a powerful diagnostic tool for C4 photosynthesis.
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Affiliation(s)
- Hugo Alonso-Cantabrana
- Division of Plant Sciences, Research School of Biology, The Australian National University, Canberra, ACT 0200, Australia
| | - Susanne von Caemmerer
- Division of Plant Sciences, Research School of Biology, The Australian National University, Canberra, ACT 0200, Australia
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Pinto H, Powell JR, Sharwood RE, Tissue DT, Ghannoum O. Variations in nitrogen use efficiency reflect the biochemical subtype while variations in water use efficiency reflect the evolutionary lineage of C4 grasses at inter-glacial CO2. PLANT, CELL & ENVIRONMENT 2016; 39:514-26. [PMID: 26381794 DOI: 10.1111/pce.12636] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/29/2014] [Revised: 08/21/2015] [Accepted: 09/05/2015] [Indexed: 05/09/2023]
Abstract
C4 photosynthesis evolved multiple times in diverse lineages. Most physiological studies comparing C4 plants were not conducted at the low atmospheric CO2 prevailing during their evolution. Here, 24 C4 grasses belonging to three biochemical subtypes [nicotinamide adenine dinucleotide malic enzyme (NAD-ME), phosphoenolpyruvate carboxykinase (PCK) and nicotinamide adenine dinucleotide phosphate malic enzyme (NADP-ME)] and six major evolutionary lineages were grown under ambient (400 μL L(-1) ) and inter-glacial (280 μL L(-1) ) CO2 . We hypothesized that nitrogen-related and water-related physiological traits are associated with subtypes and lineages, respectively. Photosynthetic rate and stomatal conductance were constrained by the shared lineage, while variation in leaf mass per area (LMA), leaf N per area, plant dry mass and plant water use efficiency were influenced by the subtype. Subtype and lineage were equally important for explaining variations in photosynthetic nitrogen use efficiency (PNUE) and photosynthetic water use efficiency (PWUE). CO2 treatment impacted most parameters. Overall, higher LMA and leaf N distinguished the Chloridoideae/NAD-ME group, while NADP-ME and PCK grasses were distinguished by higher PNUE regardless of lineage. Plants were characterized by high photosynthesis and PWUE when grown at ambient CO2 and by high conductance at inter-glacial CO2 . In conclusion, the evolutionary and biochemical diversity among C4 grasses was aligned with discernible leaf physiology, but it remains unknown whether these traits represent ecophysiological adaptation.
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Affiliation(s)
- Harshini Pinto
- Hawkesbury Institute for the Environment, Western Sydney University, Locked Bag 1797, Penrith, NSW, 2751, Australia
| | - Jeff R Powell
- Hawkesbury Institute for the Environment, Western Sydney University, Locked Bag 1797, Penrith, NSW, 2751, Australia
| | - Robert E Sharwood
- Hawkesbury Institute for the Environment, Western Sydney University, Locked Bag 1797, Penrith, NSW, 2751, Australia
- Research School of Biology, Australian National University, Canberra, ACT, 2601, Australia
| | - David T Tissue
- Hawkesbury Institute for the Environment, Western Sydney University, Locked Bag 1797, Penrith, NSW, 2751, Australia
| | - Oula Ghannoum
- Hawkesbury Institute for the Environment, Western Sydney University, Locked Bag 1797, Penrith, NSW, 2751, Australia
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von Caemmerer S, Ghannoum O, Pengelly JJL, Cousins AB. Carbon isotope discrimination as a tool to explore C4 photosynthesis. JOURNAL OF EXPERIMENTAL BOTANY 2014; 65:3459-70. [PMID: 24711615 DOI: 10.1093/jxb/eru127] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
Photosynthetic carbon isotope discrimination is a non-destructive tool for investigating C4 metabolism. Tuneable diode laser absorption spectroscopy provides new opportunities for making rapid, concurrent measurements of carbon isotope discrimination and CO2 assimilation over a range of environmental conditions, and this has facilitated the use of carbon isotope discrimination as a probe of C4 metabolism. In spite of the significant progress made in recent years, understanding how photosynthetic carbon isotope discrimination measured concurrently with gas exchange relates to carbon isotope composition of leaf and plant dry matter remains a challenge that requires resolution if this technique is to be successfully applied as a screening tool in crop breeding and phylogenetic research. In this review, we update our understanding of the factors and assumptions that underlie variations in photosynthetic carbon isotope discrimination in C4 leaves. Closing the main gaps in our understanding of carbon isotope discrimination during C4 photosynthesis may help advance research aimed at developing higher productivity and efficiency in key C4 food, feed, and biofuel crops.
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Affiliation(s)
- Susanne von Caemmerer
- Research School of Biology, The Australian National University, Canberra ACT 0200, Australia
| | - Oula Ghannoum
- Hawkesbury Institute for the Environment, University of Western Sydney, Hawkesbury campus, Locked Bag 1797, Penrith 2751, NSW, Australia
| | - Jasper J L Pengelly
- Research School of Biology, The Australian National University, Canberra ACT 0200, Australia
| | - Asaph B Cousins
- School of Biological Sciences, Washington State University, Pullman, WA 99164, USA
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Pinto H, Sharwood RE, Tissue DT, Ghannoum O. Photosynthesis of C3, C3-C4, and C4 grasses at glacial CO2. JOURNAL OF EXPERIMENTAL BOTANY 2014; 65:3669-81. [PMID: 24723409 PMCID: PMC4085965 DOI: 10.1093/jxb/eru155] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Most physiology comparisons of C3 and C4 plants are made under current or elevated concentrations of atmospheric CO2 which do not reflect the low CO2 environment under which C4 photosynthesis has evolved. Accordingly, photosynthetic nitrogen (PNUE) and water (PWUE) use efficiency, and the activity of the photosynthetic carboxylases [Rubisco and phosphoenolpyruvate carboxylase (PEPC)] and decarboxylases [NADP-malic enzyme (NADP-ME) and phosphoenolpyruvate carboxykinase (PEP-CK)] were compared in eight C4 grasses with NAD-ME, PCK, and NADP-ME subtypes, one C3 grass, and one C3-C4 grass grown under ambient (400 μl l(-1)) and glacial (180 μl l(-1)) CO2. Glacial CO2 caused a smaller reduction of photosynthesis and a greater increase of stomatal conductance in C4 relative to C3 and C3-C4 species. Panicum bisulcatum (C3) acclimated to glacial [CO2] by doubling Rubisco activity, while Rubisco was unchanged in Panicum milioides (C3-C4), possibly due to its high leaf N and Rubisco contents. Glacial CO2 up-regulated Rubisco and PEPC activities in concert for several C4 grasses, while NADP-ME and PEP-CK activities were unchanged, reflecting the high control exerted by the carboxylases relative to the decarboxylases on the efficiency of C4 metabolism. Despite having larger stomatal conductance at glacial CO2, C4 species maintained greater PWUE and PNUE relative to C3-C4 and C3 species due to higher photosynthetic rates. Relative to other C4 subtypes, NAD-ME and PEP-CK grasses had the highest PWUE and PNUE, respectively; relative to C3, the C3-C4 grass had higher PWUE and similar PNUE at glacial CO2. Biomass accumulation was reduced by glacial CO2 in the C3 grass relative to the C3-C4 grass, while biomass was less reduced in NAD-ME grasses compared with NADP-ME and PCK grasses. Under glacial CO2, high resource use efficiency offers a key evolutionary advantage for the transition from C3 to C4 photosynthesis in water- and nutrient-limited environments.
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Affiliation(s)
- Harshini Pinto
- Hawkesbury Institute for the Environment, University of Western Sydney, Hawkesbury campus, Locked Bag 1797, Penrith 2751, NSW, Australia
| | - Robert E Sharwood
- Hawkesbury Institute for the Environment, University of Western Sydney, Hawkesbury campus, Locked Bag 1797, Penrith 2751, NSW, Australia
| | - David T Tissue
- Hawkesbury Institute for the Environment, University of Western Sydney, Hawkesbury campus, Locked Bag 1797, Penrith 2751, NSW, Australia
| | - Oula Ghannoum
- Hawkesbury Institute for the Environment, University of Western Sydney, Hawkesbury campus, Locked Bag 1797, Penrith 2751, NSW, Australia
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41
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Sharwood RE, Sonawane BV, Ghannoum O. Photosynthetic flexibility in maize exposed to salinity and shade. JOURNAL OF EXPERIMENTAL BOTANY 2014; 65:3715-24. [PMID: 24692650 PMCID: PMC4085963 DOI: 10.1093/jxb/eru130] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
C4 photosynthesis involves a close collaboration of the C3 and C4 metabolic cycles across the mesophyll and bundle-sheath cells. This study investigated the coordination of C4 photosynthesis in maize plants subjected to two salinity (50 and 100mM NaCl) treatments and one shade (20% of full sunlight) treatment. Photosynthetic efficiency was probed by combining leaf gas-exchange measurements with carbon isotope discrimination and assaying the key carboxylases [ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and phosphoenolpyruvate carboxylase (PEPC)] and decarboxylases [nicotinamide adenine dinucleotide phosphate malic enzyme (NADP-ME) and phosphoenolpyruvate carboxykinase (PEP-CK)] operating in maize leaves. Generally, salinity inhibited plant growth and photosynthesis to a lesser extent than shade. Salinity reduced photosynthesis primarily by reducing stomatal conductance and secondarily by equally reducing Rubisco and PEPC activities; the decarboxylases were inhibited more than the carboxylases. Salinity increased photosynthetic carbon isotope discrimination (Δp) and reduced leaf dry-matter carbon isotope composition ((13)δ) due to changes in p i/p a (intercellular to ambient CO2 partial pressure), while CO2 leakiness out of the bundle sheath (ϕ) was similar to that in control plants. Acclimation to shade was underpinned by a greater downregulation of PEPC relative to Rubisco activity, and a lesser inhibition of NADP-ME (primary decarboxylase) relative to PEP-CK (secondary decarboxylase). Shade reduced Δp and ɸ without significantly affecting leaf (13)δ or p i/p a relative to control plants. Accordingly, shade perturbed the balance between the C3 and C4 cycles during photosynthesis in maize, and demonstrated the flexible partitioning of C4 acid decarboxylation activity between NADP-ME and PEP-CK in response to the environment. This study highlights the need to improve our understanding of the links between leaf (13)δ and photosynthetic Δp, and the role of the secondary decarboxylase PEP-CK in NADP-ME plants such as maize.
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Affiliation(s)
- Robert E Sharwood
- Hawkesbury Institute for the Environment, University of Western Sydney, Richmond, Locked bag 1797, Penrith NSW 2751, Australia
| | - Balasaheb V Sonawane
- Hawkesbury Institute for the Environment, University of Western Sydney, Richmond, Locked bag 1797, Penrith NSW 2751, Australia
| | - Oula Ghannoum
- Hawkesbury Institute for the Environment, University of Western Sydney, Richmond, Locked bag 1797, Penrith NSW 2751, Australia
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42
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Kromdijk J, Ubierna N, Cousins AB, Griffiths H. Bundle-sheath leakiness in C4 photosynthesis: a careful balancing act between CO2 concentration and assimilation. JOURNAL OF EXPERIMENTAL BOTANY 2014; 65:3443-57. [PMID: 24755278 DOI: 10.1093/jxb/eru157] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Crop species with the C4 photosynthetic pathway are generally characterized by high productivity, especially in environmental conditions favouring photorespiration. In comparison with the ancestral C3 pathway, the biochemical and anatomical modifications of the C4 pathway allow spatial separation of primary carbon acquisition in mesophyll cells and subsequent assimilation in bundle-sheath cells. The CO2-concentrating C4 cycle has to operate in close coordination with CO2 reduction via the Calvin-Benson-Bassham (CBB) cycle in order to keep the C4 pathway energetically efficient. The gradient in CO2 concentration between bundle-sheath and mesophyll cells facilitates diffusive leakage of CO2. This rate of bundle-sheath CO2 leakage relative to the rate of phosphoenolpyruvate carboxylation (termed leakiness) has been used to probe the balance between C4 carbon acquisition and subsequent reduction as a result of environmental perturbations. When doing so, the correct choice of equations to derive leakiness from stable carbon isotope discrimination (Δ(13)C) during gas exchange is critical to avoid biased results. Leakiness responses to photon flux density, either short-term (during measurements) or long-term (during growth and development), can have important implications for C4 performance in understorey light conditions. However, recent reports show leakiness to be subject to considerable acclimation. Additionally, the recent discovery of two decarboxylating C4 cycles operating in parallel in Zea mays suggests that flexibility in the transported C4 acid and associated decarboxylase could also aid in maintaining C4/CBB balance in a changing environment. In this paper, we review improvements in methodology to estimate leakiness, synthesize reports on bundle-sheath leakiness, discuss different interpretations, and highlight areas where future research is necessary.
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Affiliation(s)
- Johannes Kromdijk
- Institute for Genomic Biology, University of Illinois, 1206W Gregory drive, Urbana, IL 61801, USA
| | - Nerea Ubierna
- Research School of Biology, The Australian National University, Canberra, ACT, Australia
| | - Asaph B Cousins
- School of Biological Sciences, Washington State University, Pullman, WA99164-4236, USA
| | - Howard Griffiths
- Physiological Ecology Group, Department of Plant Sciences, University of Cambridge, Downing Street, Cambridge CB23EA, UK
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Studer AJ, Gandin A, Kolbe AR, Wang L, Cousins AB, Brutnell TP. A Limited Role for Carbonic Anhydrase in C4 Photosynthesis as Revealed by a ca1ca2 Double Mutant in Maize. PLANT PHYSIOLOGY 2014; 165:608-617. [PMID: 24706552 PMCID: PMC4044840 DOI: 10.1104/pp.114.237602] [Citation(s) in RCA: 67] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/11/2014] [Accepted: 04/03/2014] [Indexed: 05/19/2023]
Abstract
Carbonic anhydrase (CA) catalyzes the first biochemical step of the carbon-concentrating mechanism of C4 plants, and in C4 monocots it has been suggested that CA activity is near limiting for photosynthesis. Here, we test this hypothesis through the characterization of transposon-induced mutant alleles of Ca1 and Ca2 in maize (Zea mays). These two isoforms account for more than 85% of the CA transcript pool. A significant change in isotopic discrimination is observed in mutant plants, which have as little as 3% of wild-type CA activity, but surprisingly, photosynthesis is not reduced under current or elevated CO2 partial pressure (pCO2). However, growth and rates of photosynthesis under subambient pCO2 are significantly impaired in the mutants. These findings suggest that, while CA is not limiting for C4 photosynthesis in maize at current pCO2, it likely maintains high rates of photosynthesis when CO2 availability is reduced. Current atmospheric CO2 levels now exceed 400 ppm (approximately 40.53 Pa) and contrast with the low-pCO2 conditions under which C4 plants expanded their range approximately 10 million years ago, when the global atmospheric CO2 was below 300 ppm (approximately 30.4 Pa). Thus, as CO2 levels continue to rise, selective pressures for high levels of CA may be limited to arid climates where stomatal closure reduces CO2 availability to the leaf.
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Affiliation(s)
- Anthony J Studer
- Donald Danforth Plant Science Center, St. Louis, Missouri 63132 (A.J.S., A.R.K., L.W., T.P.B.); andSchool of Biological Sciences, Washington State University, Pullman, Washington 99164 (A.G., A.B.C.)
| | - Anthony Gandin
- Donald Danforth Plant Science Center, St. Louis, Missouri 63132 (A.J.S., A.R.K., L.W., T.P.B.); andSchool of Biological Sciences, Washington State University, Pullman, Washington 99164 (A.G., A.B.C.)
| | - Allison R Kolbe
- Donald Danforth Plant Science Center, St. Louis, Missouri 63132 (A.J.S., A.R.K., L.W., T.P.B.); andSchool of Biological Sciences, Washington State University, Pullman, Washington 99164 (A.G., A.B.C.)
| | - Lin Wang
- Donald Danforth Plant Science Center, St. Louis, Missouri 63132 (A.J.S., A.R.K., L.W., T.P.B.); andSchool of Biological Sciences, Washington State University, Pullman, Washington 99164 (A.G., A.B.C.)
| | - Asaph B Cousins
- Donald Danforth Plant Science Center, St. Louis, Missouri 63132 (A.J.S., A.R.K., L.W., T.P.B.); andSchool of Biological Sciences, Washington State University, Pullman, Washington 99164 (A.G., A.B.C.)
| | - Thomas P Brutnell
- Donald Danforth Plant Science Center, St. Louis, Missouri 63132 (A.J.S., A.R.K., L.W., T.P.B.); andSchool of Biological Sciences, Washington State University, Pullman, Washington 99164 (A.G., A.B.C.)
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Stutz SS, Edwards GE, Cousins AB. Single-cell C(4) photosynthesis: efficiency and acclimation of Bienertia sinuspersici to growth under low light. THE NEW PHYTOLOGIST 2014; 202:220-232. [PMID: 24384064 DOI: 10.1111/nph.12648] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/22/2013] [Accepted: 11/13/2013] [Indexed: 06/03/2023]
Abstract
Traditionally, it was believed that C(4) photosynthesis required two types of chlorenchyma cells to concentrate CO(2) within the leaf. However, several species have been identified that perform C(4) photosynthesis using dimorphic chloroplasts within an individual cell. The goal of this research was to determine how growth under limited light affects leaf structure, biochemistry and efficiency of the single-cell CO(2) -concentrating mechanism in Bienertia sinuspersici. Measurements of rates of CO(2) assimilation and CO(2) isotope exchange in response to light intensity and O(2) were used to determine the efficiency of the CO(2) -concentrating mechanism in plants grown under moderate and low light. In addition, enzyme assays, chlorophyll content and light microscopy of leaves were used to characterize acclimation to light-limited growth conditions. There was acclimation to growth under low light with a decrease in capacity for photosynthesis when exposed to high light. This was associated with a decreased investment in biochemistry for carbon assimilation with only subtle changes in leaf structure and anatomy. The capture and assimilation of CO(2) delivered by the C(4) cycle was lower in low-light-grown plants. Low-light-grown plants were able to acclimate to maintain structural and functional features for the performance of efficient single-cell C(4) photosynthesis.
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Affiliation(s)
- Samantha S Stutz
- School of Biological Sciences, Washington State University, Pullman, WA, 99164, USA
| | - Gerald E Edwards
- School of Biological Sciences, Washington State University, Pullman, WA, 99164, USA
| | - Asaph B Cousins
- School of Biological Sciences, Washington State University, Pullman, WA, 99164, USA
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Kubásek J, Urban O, Šantrůček J. C4 plants use fluctuating light less efficiently than do C3 plants: a study of growth, photosynthesis and carbon isotope discrimination. PHYSIOLOGIA PLANTARUM 2013; 149:528-39. [PMID: 23550566 DOI: 10.1111/ppl.12057] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/18/2013] [Revised: 03/21/2013] [Accepted: 03/24/2013] [Indexed: 05/12/2023]
Abstract
Plants in the field are commonly exposed to fluctuating light intensity, caused by variable cloud cover, self-shading of leaves in the canopy and/or leaf movement due to turbulence. In contrast to C3 plant species, only little is known about the effects of dynamic light (DL) on photosynthesis and growth in C4 plants. Two C4 and two C3 monocot and eudicot species were grown under steady light or DL conditions with equal sum of daily incident photon flux. We measured leaf gas exchange, plant growth and dry matter carbon isotope discrimination to infer CO2 bundle sheath leakiness in C4 plants. The growth of all species was reduced by DL, despite only small changes in steady-state gas exchange characteristics, and this effect was more pronounced in C4 than C3 species due to lower assimilation at light transitions. This was partially attributed to increased bundle sheath leakiness in C4 plants under the simulated lightfleck conditions. We hypothesize that DL leads to imbalances in the coordination of C4 and C3 cycles and increasing leakiness, thereby decreasing the quantum efficiency of photosynthesis. In addition to their other constraints, the inability of C4 plants to efficiently utilize fluctuating light likely contributes to their absence in such environments as forest understoreys.
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Affiliation(s)
- Jiří Kubásek
- Global Change Research Centre, Academy of Sciences of the Czech Republic, Brno, Czech Republic
- The University of South Bohemia, Faculty of Science, CZ-370 05, České Budějovice, Czech Republic
| | - Otmar Urban
- Global Change Research Centre, Academy of Sciences of the Czech Republic, Brno, Czech Republic
| | - Jiří Šantrůček
- The University of South Bohemia, Faculty of Science, CZ-370 05, České Budějovice, Czech Republic
- Biology Centre, Academy of Sciences of the Czech Republic, Institute of Plant Molecular Biology, CZ-370 05, České Budějovice, Czech Republic
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Cernusak LA, Ubierna N, Winter K, Holtum JAM, Marshall JD, Farquhar GD. Environmental and physiological determinants of carbon isotope discrimination in terrestrial plants. THE NEW PHYTOLOGIST 2013; 200:950-65. [PMID: 23902460 DOI: 10.1111/nph.12423] [Citation(s) in RCA: 232] [Impact Index Per Article: 21.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/31/2013] [Accepted: 06/25/2013] [Indexed: 05/05/2023]
Abstract
Stable carbon isotope ratios (δ(13) C) of terrestrial plants are employed across a diverse range of applications in environmental and plant sciences; however, the kind of information that is desired from the δ(13) C signal often differs. At the extremes, it ranges between purely environmental and purely biological. Here, we review environmental drivers of variation in carbon isotope discrimination (Δ) in terrestrial plants, and the biological processes that can either damp or amplify the response. For C3 plants, where Δ is primarily controlled by the ratio of intercellular to ambient CO2 concentrations (ci /ca ), coordination between stomatal conductance and photosynthesis and leaf area adjustment tends to constrain the potential environmentally driven range of Δ. For C4 plants, variation in bundle-sheath leakiness to CO2 can either damp or amplify the effects of ci /ca on Δ. For plants with crassulacean acid metabolism (CAM), Δ varies over a relatively large range as a function of the proportion of daytime to night-time CO2 fixation. This range can be substantially broadened by environmental effects on Δ when carbon uptake takes place primarily during the day. The effective use of Δ across its full range of applications will require a holistic view of the interplay between environmental control and physiological modulation of the environmental signal.
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Affiliation(s)
- Lucas A Cernusak
- Department of Marine and Tropical Biology, James Cook University, Cairns, Qld, Australia
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47
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Ubierna N, Sun W, Kramer DM, Cousins AB. The efficiency of C4 photosynthesis under low light conditions in Zea mays, Miscanthus x giganteus and Flaveria bidentis. PLANT, CELL & ENVIRONMENT 2013; 36:365-81. [PMID: 22812384 DOI: 10.1111/j.1365-3040.2012.02579.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/08/2023]
Abstract
The efficiency of C(4) photosynthesis in Zea mays, Miscanthus x giganteus and Flaveria bidentis in response to light was determined using measurements of gas exchange, (13) CO(2) photosynthetic discrimination, metabolite pools and spectroscopic assays, with models of C(4) photosynthesis and leaf (13) CO(2) discrimination. Spectroscopic and metabolite assays suggested constant energy partitioning between the C(4) and C(3) cycles across photosynthetically active radiation (PAR). Leakiness (φ), modelled using C(4) light-limited photosynthesis equations (φ(mod)), matched values from the isotope method without simplifications (φ(is)) and increased slightly from high to low PAR in all species. However, simplifications of bundle-sheath [CO(2)] and respiratory fractionation lead to large overestimations of φ at low PAR with the isotope method. These species used different strategies to maintain similar φ. For example, Z. mays had large rates of the C(4) cycle and low bundle-sheath cells CO(2 ) conductance (g(bs)). While F. bidentis had larger g(bs) but lower respiration rates and M. giganteus had less C(4) cycle capacity but low g(bs), which resulted in similar φ. This demonstrates that low g(bs) is important for efficient C(4) photosynthesis but it is not the only factor determining φ. Additionally, these C(4) species are able to optimize photosynthesis and minimize φ over a range of PARs, including low light.
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Affiliation(s)
- Nerea Ubierna
- School of Biological Sciences, Molecular Plant Sciences, Washington State University, Pullman, WA 99164-4236, USA
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King JL, Edwards GE, Cousins AB. The efficiency of the CO2-concentrating mechanism during single-cell C4 photosynthesis. PLANT, CELL & ENVIRONMENT 2012; 35:513-523. [PMID: 21950797 DOI: 10.1111/j.1365-3040.2011.02431.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
The photosynthetic efficiency of the CO(2)-concentrating mechanism in two forms of single-cell C(4) photosynthesis in the family Chenopodiaceae was characterized. The Bienertioid-type single-cell C(4) uses peripheral and central cytoplasmic compartments (Bienertia sinuspersici), while the Borszczowioid single-cell C(4) uses distal and proximal compartments of the cell (Suaeda aralocaspica). C(4) photosynthesis within a single-cell raises questions about the efficiency of this type of CO(2) -concentrating mechanism compared with the Kranz-type. We used measurements of leaf CO(2) isotope exchange (Δ(13) C) to compare the efficiency of the single-cell and Kranz-type forms of C(4) photosynthesis under various temperature and light conditions. Comparisons were made between the single-cell C(4) and a sister Kranz form, S. eltonica[NAD malic enzyme (NAD ME) type], and with Flaveria bidentis[NADP malic enzyme (NADP-ME) type with Kranz Atriplicoid anatomy]. There were similar levels of Δ(13) C discrimination and CO(2) leakiness (Φ) in the single-cell species compared with the Kranz-type. Increasing leaf temperature (25 to 30 °C) and light intensity caused a decrease in Δ(13) C and Φ across all C(4) types. Notably, B. sinuspersici had higher Δ(13) C and Φ than S. aralocaspica under lower light. These results demonstrate that rates of photosynthesis and efficiency of the CO(2) -concentrating mechanisms in single-cell C(4) plants are similar to those in Kranz-type.
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Affiliation(s)
- Jenny L King
- School of Biological Sciences, Washington State University, Pullman, WA 99164-4236, USA
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New grass phylogeny resolves deep evolutionary relationships and discovers C4 origins. THE NEW PHYTOLOGIST 2012; 193:304-12. [PMID: 22115274 DOI: 10.1111/j.1469-8137.2011.03972.x] [Citation(s) in RCA: 258] [Impact Index Per Article: 21.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/19/2023]
Abstract
• Grasses rank among the world's most ecologically and economically important plants. Repeated evolution of the C(4) syndrome has made photosynthesis highly efficient in many grasses, inspiring intensive efforts to engineer the pathway into C(3) crops. However, comparative biology has been of limited use to this endeavor because of uncertainty in the number and phylogenetic placement of C(4) origins. • We built the most comprehensive and robust molecular phylogeny for grasses to date, expanding sampling efforts of a previous working group from 62 to 531 taxa, emphasizing the C(4)-rich PACMAD (Panicoideae, Arundinoideae, Chloridoideae, Micrairoideae, Aristidoideae and Danthonioideae) clade. Our final matrix comprises c. 5700 bp and is > 93% complete. • For the first time, we present strong support for relationships among all the major grass lineages. Several new C(4) lineages are identified, and previously inferred origins confirmed. C(3)/C(4) evolutionary transitions have been highly asymmetrical, with 22-24 inferred origins of the C(4) pathway and only one potential reversal. • Our backbone tree clarifies major outstanding systematic questions and highlights C(3) and C(4) sister taxa for comparative studies. Two lineages have emerged as hotbeds of C(4) evolution. Future work in these lineages will be instrumental in understanding the evolution of this complex trait.
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Ubierna N, Sun W, Cousins AB. The efficiency of C(4) photosynthesis under low light conditions: assumptions and calculations with CO(2) isotope discrimination. JOURNAL OF EXPERIMENTAL BOTANY 2011; 62:3119-34. [PMID: 21527629 DOI: 10.1093/jxb/err073] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
Leakiness (Φ), the proportion of carbon fixed by phosphoenolpyruvate carboxylation that leaks out of the bundle-sheath cells, determines C(4) photosynthetic efficiency. Large increases in Φ have been described at low irradiance. The underlying mechanisms for this increase remain uncertain, but changes in photorespiration or the energy partitioning between the C(4) and C(3) cycles have been suggested. Additionally, values of Φ at low light could be magnified from assumptions made when comparing measured photosynthetic discrimination against (13)C (Δ) with the theoretical formulation for Δ. For example, several simplifications are often made when modelling Δ to predict Φ including: (i) negligible fractionation during photorespiration and dark respiration; (ii) infinite mesophyll conductance; and (iii) CO(2) inside bundle-sheath cells (C(s)) is much larger than values in mesophyll cells (C(m)). Theoretical models for C(4) photosynthesis and C(4) Δ were combined to evaluate how these simplifications affect calculations of Δ and Φ at different light intensities. It was demonstrated that the effects of photorespiratory fractionations and mesophyll conductance were negligible at low light. Respiratory fractionation was relevant only when the magnitude of the fractionation factor was artificially increased during measurements. The largest error in estimating Φ occurred when assuming C(s) was much larger than C(m) at low light levels, when bundle-sheath conductance was large (g(s)), or at low O(2) concentrations. Under these conditions, the simplified equation for Δ overestimated Φ, and compromised comparisons between species with different g(s), and comparisons across O(2) concentrations.
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Affiliation(s)
- Nerea Ubierna
- School of Biological Sciences, Molecular Plant Sciences, Washington State University, Pullman, WA 99164-4236, USA.
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