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Rubisco without the Calvin cycle improves the carbon efficiency of developing green seeds

Abstract

Efficient storage of carbon in seeds is crucial to plant fitness and to agricultural productivity. Oil is a major reserve material in most seeds1, and these oils provide the largest source of renewable reduced carbon chains available from nature. However, the conversion of carbohydrate to oil through glycolysis results in the loss of one-third of the carbon as CO2. Here we show that, in developing embryos of Brassica napus L. (oilseed rape), Rubisco (ribulose 1,5-bisphosphate carboxylase/oxygenase) acts without the Calvin cycle2 and in a previously undescribed metabolic context to increase the efficiency of carbon use during the formation of oil. In comparison with glycolysis, the metabolic conversion we describe provides 20% more acetyl-CoA for fatty-acid synthesis and results in 40% less loss of carbon as CO2. Our conclusions are based on measurements of mass balance, enzyme activity and stable isotope labelling, as well as an analysis of elementary flux modes.

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Figure 1: Metabolic transformation of sugars into fatty acids.
Figure 2: Light-dependent ratio of oil synthesis and CO2 production.

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Acknowledgements

This work was supported by grants from the Department of Energy, the National Science Foundation and the USDA. Acknowledgement is also made to the Michigan Agricultural Experiment Station for its support of this research.

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Correspondence to Jörg Schwender.

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The authors declare that they have no competing financial interests.

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Supplementary Notes

Contains an analysis of how much carbon dioxide can be assimilated and stored in biomass by carboxylation reactions that produce oxaloacetate. Alternative metabolic routes for converting hexose into acetyl-CoA are described and analysed as elementary flux modes. The labelling experiments using 13CO2 or 13C-labelled alanine are discussed with additional detail. (DOC 354 kb)

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Schwender, J., Goffman, F., Ohlrogge, J. et al. Rubisco without the Calvin cycle improves the carbon efficiency of developing green seeds. Nature 432, 779–782 (2004). https://doi.org/10.1038/nature03145

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