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Peer-reviewedCC BYThe Plant Cell

Mitochondrial glutamine synthetase overexpression in tomato source leaves increases assimilate export and fruit yield

  • José Gabriel Vallarino1,2
  • Laíse Rosado-Souza2
  • Youjun Zhang3,4
  • R. George Ratcliffe5
  • Lee James Sweetlove5
  • Sanu Shameer5,6
  • Alisdair Robert Fernie7,2
7 affiliations
  1. 1Faculty of Sciences, University of Málaga, IHSM-UMA-CSIC Campus Teatinos , Málaga ,
  2. 2Max Planck Institute for Molecular Plant Physiology , Potsdam-Golm ,
  3. 3College of Advanced Agricultural Sciences, University of Chinese Academy of Sciences , Beijing ,
  4. 4State Key Laboratory of Seed Innovation, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences , Beijing ,
  5. 5Department of Plant Sciences, University of Oxford , Oxford ,
  6. 6School of Biology, Indian Institute of Science Education and Research Thiruvananthapuram , Maruthamala P.O., Kerala ,
  7. 7Center of Plant Systems Biology and Biotechnology , Plovdiv ,
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Abstract

To identify potential strategies for increasing the efficiency of tomato leaf metabolism with a focus on the links between nitrogen/carbon metabolism, we explored a diel flux balance analysis (FBA) model of a source leaf in which the metabolic output was varied up to the theoretically achievable maximum. We noticed a potentially interesting switch in the use of glutamine synthetase (GS) isoforms-from the chloroplast isoform to the mitochondrial one-for nitrogen assimilation. To further explore this prediction, we characterized transgenic tomato plants as overexpressing 2 tomato GS genes, GS1 and GS2, targeted to mitochondria. Both sets of transgenic plants were characterized as displaying faster growth rate, early flowering, and increased fruit yield. In leaves, metabolomic profiling and enzyme activity analysis pointed out that GS activity in mitochondria plays a role in increasing the intracellular synthesis and subsequent export of sugar. Consistent with these changes, higher sucrose concentration in leaf exudates and reduced activities of enzymes involved in leaf starch synthesis were observed. Moreover, mitochondrial GS activity affected chloroplast redox status in a manner that modulated photorespiration and nitrogen metabolism. The combined data reveal the influence of mitochondrial GS activity on both foliar carbon/nitrogen balance and regulation of source-sink metabolism in tomato plants.

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Cite

BibTeXRIS
BibTeX
@article{vallarino2026mitochondrial,
  title = {{Mitochondrial glutamine synthetase overexpression in tomato source leaves increases assimilate export and fruit yield}},
  author = {José Gabriel Vallarino and Laíse Rosado-Souza and Youjun Zhang and R. George Ratcliffe and Lee James Sweetlove and Sanu Shameer and Alisdair Robert Fernie},
  journal = {The Plant Cell},
  year = {2026},
  month = jun,
  doi = {10.1093/plcell/koag181},
  url = {https://doi.org/10.1093/plcell/koag181},
  note = {CC BY},
}
RIS
TY  - JOUR
TI  - Mitochondrial glutamine synthetase overexpression in tomato source leaves increases assimilate export and fruit yield
AU  - José Gabriel Vallarino
AU  - Laíse Rosado-Souza
AU  - Youjun Zhang
AU  - R. George Ratcliffe
AU  - Lee James Sweetlove
AU  - Sanu Shameer
AU  - Alisdair Robert Fernie
PY  - 2026
DA  - 2026/06/13
JO  - The Plant Cell
DO  - 10.1093/plcell/koag181
UR  - https://doi.org/10.1093/plcell/koag181
AB  - To identify potential strategies for increasing the efficiency of tomato leaf metabolism with a focus on the links between nitrogen/carbon metabolism, we explored a diel flux balance analysis (FBA) model of a source leaf in which the metabolic output was varied up to the theoretically achievable maximum. We noticed a potentially interesting switch in the use of glutamine synthetase (GS) isoforms-from the chloroplast isoform to the mitochondrial one-for nitrogen assimilation. To further explore this prediction, we characterized transgenic tomato plants as overexpressing 2 tomato GS genes, GS1 and GS2, targeted to mitochondria. Both sets of transgenic plants were characterized as displaying faster growth rate, early flowering, and increased fruit yield. In leaves, metabolomic profiling and enzyme activity analysis pointed out that GS activity in mitochondria plays a role in increasing the intracellular synthesis and subsequent export of sugar. Consistent with these changes, higher sucrose concentration in leaf exudates and reduced activities of enzymes involved in leaf starch synthesis were observed. Moreover, mitochondrial GS activity affected chloroplast redox status in a manner that modulated photorespiration and nitrogen metabolism. The combined data reveal the influence of mitochondrial GS activity on both foliar carbon/nitrogen balance and regulation of source-sink metabolism in tomato plants.
SN  - 1040-4651
SN  - 1532-298X
ER  -