Abstract
Although the mitochondria retain all required enzymes for an intact tricarboxylic acid (TCA) cycle, plants might shift the cyclic flux from the TCA cycle to an alternative noncyclic pathway via γ-aminobutyric acid (GABA) shunt under specific physiological conditions. We hypothesize that several genes may ease this noncyclic flux and contribute to the citrus response to the phytopathogenic bacterium ‘Candidatus Liberibacter asiaticus’, the causal agent of Huanglongbing in citrus. To test this hypothesis, we used multiomics techniques (metabolomics, fluxomics, and transcriptomics) to investigate the potential roles of putative gab homologies from Valencia sweet orange (Citrus sinensis). Our findings showed that ‘Ca. L. asiaticus’ significantly increased the endogenous GABA and succinate content but decreased ketoglutarate in infected citrus plants. Citrus genome harbors three putative gab genes, including amino-acid permease (also known as GABA permease; CsgabP), GABA transaminase (CsgabT), and succinate-semialdehyde dehydrogenase (also known as GABA dehydrogenase; CsgabD). The transcript levels of CsgabP, CsgabT, and CsgabD were upregulated in citrus leaves upon the infection with ‘Ca. L. asiaticus’ and after the exogenous application of GABA or deuterium-labeled GABA isotope (GABA-D 6 ). Moreover, our finding showed that exogenously applied GABA is quickly converted to succinate and fed into the TCA cycle. Likewise, the fluxomics study showed that GABA-D 6 is rapidly metabolized to succinate-D 4 . Our work proved that GABA shunt and three predicated gab genes from citrus, support the upstream noncyclic flux toward succinate rather than an intact TCA cycle and contribute to citrus defense responses to ‘Ca. L. asiaticus’. [Formula: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .
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Claims 10
Claim · model-written summary
Infection increased endogenous GABA in citrus.
- Treatment
- ‘Ca. L. asiaticus’e0
- Interactor
- ‘Ca. L. asiaticus’e0pathogen
- Outcome
- endogenous GABAe0
- Direction
- increasede0
CitrusNot reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“‘Ca. L. asiaticus’ significantly increased the endogenous GABA and succinate content but decreased ketoglutarate in infected citrus plants”
Claim · model-written summary
Infection increased succinate in citrus.
- Treatment
- ‘Ca. L. asiaticus’e0
- Interactor
- ‘Ca. L. asiaticus’e0pathogen
- Outcome
- succinate contente0
- Direction
- increasede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“‘Ca. L. asiaticus’ significantly increased the endogenous GABA and succinate content but decreased ketoglutarate in infected citrus plants”
Claim · model-written summary
Infection decreased ketoglutarate in citrus.
- Treatment
- ‘Ca. L. asiaticus’e0
- Interactor
- ‘Ca. L. asiaticus’e0pathogen
- Outcome
- ketoglutaratee0
- Direction
- decreasede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“‘Ca. L. asiaticus’ significantly increased the endogenous GABA and succinate content but decreased ketoglutarate in infected citrus plants”
Claim · model-written summary
The citrus genome contained three putative gab genes.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Citrus genome harbors three putative gab genes, including amino-acid permease (also known as GABA permease; CsgabP), GABA transaminase (CsgabT), and succinate-semialdehyde dehydrogenase (also known as GABA dehydrogenase; CsgabD)”
Claim · model-written summary
Infection upregulated CsgabP, CsgabT and CsgabD transcripts in citrus leaves.
- Organ / stage
- leavese0
- Treatment
- infection with ‘Ca. L. asiaticus’e0
- Interactor
- ‘Ca. L. asiaticus’e0pathogen
- Gene
- CsgabP, CsgabT, and CsgabDe0
- Outcome
- transcript levelse0
- Direction
- upregulatede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The transcript levels of CsgabP, CsgabT, and CsgabD were upregulated in citrus leaves upon the infection with ‘Ca. L. asiaticus’”
Claim · model-written summary
Applied GABA upregulated the three gab transcripts in citrus leaves.
- Treatment
- exogenous application of GABAe0
- Gene
- CsgabP, CsgabT, and CsgabDe0
- Outcome
- transcript levelse0
- Direction
- upregulatede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The transcript levels of CsgabP, CsgabT, and CsgabD were upregulated in citrus leaves upon the infection with ‘Ca. L. asiaticus’ and after the exogenous application of GABA or deuterium-labeled GABA isotope (GABA-D 6 )”
Claim · model-written summary
Applied GABA-D 6 upregulated the three gab transcripts in citrus leaves.
- Treatment
- deuterium-labeled GABA isotope (GABA-D 6 )e0
- Gene
- CsgabP, CsgabT, and CsgabDe0
- Outcome
- transcript levelse0
- Direction
- upregulatede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The transcript levels of CsgabP, CsgabT, and CsgabD were upregulated in citrus leaves upon the infection with ‘Ca. L. asiaticus’ and after the exogenous application of GABA or deuterium-labeled GABA isotope (GABA-D 6 )”
Claim · model-written summary
Applied GABA was rapidly converted to succinate and entered the TCA cycle.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“exogenously applied GABA is quickly converted to succinate and fed into the TCA cycle”
t0“Citrus”
Claim · model-written summary
GABA-D 6 was rapidly metabolized to succinate-D 4.
- Outcome
- metabolized to succinate-D 4e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“GABA-D 6 is rapidly metabolized to succinate-D 4”
t0“Citrus”
Claim · model-written summary
The authors concluded that the GABA shunt and three gab genes support noncyclic succinate flux and citrus defense.
- Interactor
- ‘Ca. L. asiaticus’e0pathogen
- Gene
- three predicated gab genese0
- Outcome
- upstream noncyclic flux toward succinatee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“GABA shunt and three predicated gab genes from citrus, support the upstream noncyclic flux toward succinate rather than an intact TCA cycle and contribute to citrus defense responses to ‘Ca. L. asiaticus’”
The same questions in other papers
calcium atom · molecular: metabolites · CitrusPositive and negative results
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- no effect
- positive
- positive
calcium atom · molecular: expression · CitrusResults agree
1 paper in the same direction as this paper
- positive
infection · molecular: expression · CitrusPositive and negative results
3 papers in the same direction as this paper · 2 in the opposite direction
- negative
- negative
- positive
2 papers more in this group
See all 6 papers →Claims are grouped by organism, treatment and what was measured or targeted. A paper counts as positive when any of its claims in the group is positive.