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Dissecting metabolic flux in C4 plants: experimental and theoretical approaches

Abstract

C4 photosynthesis is the carbon fixation pathway in specific plant species, so called C4 plants including maize, sorghum and sugarcane. It is characterized by the carboxylation reaction that forms four-carbon (C4) molecules, which are then used to transport CO2 to the proximity of RubisCO in the bundle sheath cells. Since C4 photosynthesis confers high photosynthetic as well as water and nitrogen use efficiency on plants, worldwide efforts have been made to understand the mechanisms of C4 photosynthesis and to properly introduce the pathway into C3 crops. Metabolic flux analysis (MFA) is a research field trying to analyze the metabolic pathway structure and activity (i.e., flux) in vivo. Constraint-based reconstruction and analysis tools theoretically study the distribution of metabolic flux in genome-scale network-based models. Different types of MFA and model-based analyses have been contributing to the discovery of C4 photosynthetic pathways and to analyze its operation in C4 plant species. This article reviews the studies to dissect the operation of C4 photosynthesis and adjacent pathways, from the pioneer studies using radioisotope-based MFA to the recent stable isotope-based MFA and the model-based approaches. These studies indicate complex interconnections among metabolic pathways and the importance of the integration of experimental and theoretical approaches. Perspectives on the integrative approach and major obstacles are also discussed.

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Abbreviations

CBB:

Calvin–Benson–Bassham

COBRA:

Constraint-based reconstruction and analysis

EMU:

Elementary metabolite units

FBA:

Flux balance analysis

GC:

Gas chromatography

GPR:

Gene-protein relationship

LC:

Liquid chromatography

MFA:

Metabolic flux analysis

MID:

Mass isotopomer distribution

MS:

Mass spectrometry

NAD-ME:

NAD+-dependent malic enzyme

NADP-ME:

NADP+-dependent malic enzyme

NMR:

Nuclear magnetic resonance

PEP:

Phosphoenolpyruvate

PEPCK:

Phosphoenolpyruvate carboxykinase

RubisCO:

Ribulose-1,5-bisphosphate carboxylase/oxygenase

TCA:

Tricarboxylic acid

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Acknowledgements

The authors are grateful to Cheryl Immethun, PhD for her input during the preparation of the manuscript. This study is based upon work supported by the Research Council Interdisciplinary Grant from University of Nebraska Lincoln (RS and TO), University of Nebraska-Lincoln Faculty Startup Grant 21-1106-4308 (RS), and the National Science Foundation/EPSCoR RII Track-2 FEC Award No. #1736192 (TO).

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Correspondence to Rajib Saha or Toshihiro Obata.

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Islam, M.M., Al-Siyabi, A., Saha, R. et al. Dissecting metabolic flux in C4 plants: experimental and theoretical approaches. Phytochem Rev 17, 1253–1274 (2018). https://doi.org/10.1007/s11101-018-9579-8

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  • DOI: https://doi.org/10.1007/s11101-018-9579-8

Keywords

  • C4 photosynthesis
  • Constraint-based reconstruction and analysis
  • Genome scale metabolic model
  • Isotope labeling
  • Metabolic flux analysis