Abstract
Abscisic acid (ABA), a plant hormone synthesized from carotenoids, functions in seed germination and abiotic stress responses. ABA is derived from the cleavage of 9-cis-isomers of violaxanthin and neoxanthin, which are oxygenated carotenoids, also called xanthophylls. Although genes encoding enzymes responsible for most steps of the ABA biosynthesis pathway have been identified, enzymatic reactions leading to the production of these cis-isomers from trans-violaxanthin remain poorly understood. Two mutants that lack trans- and cis-neoxanthin, tomato (Solanum lycopersicum) neoxanthin-deficient1 (nxd1) and Arabidopsis (Arabidopsis thaliana) ABA-deficient4 (aba4), were identified previously, but only aba4 exhibited ABA-deficient phenotypes. No enzymatic activity was detected for ABA4 and NXD1 proteins, and their exact function remained unknown. To further investigate ABA4 and NXD1 function in Arabidopsis, we compared phenotypes of single and double mutants, and analyzed the effect of ABA4 overexpression on ABA and carotenoid accumulation in wild-type and mutant backgrounds. We provide convergent evidence that ABA4 is not only required for the formation of trans- and 9′-cis-neoxanthin from trans-violaxanthin, but also controls 9-cis-violaxanthin accumulation. While nxd1 produces high amounts of 9-cis-violaxanthin and ABA, aba4 nxd1 exhibits reduced levels in both leaves and seeds. Furthermore, ABA4 constitutive expression in nxd1 increases both 9-cis-violaxanthin and ABA accumulation. Subcellular localization of NXD1 protein in transient expression assays suggests that production of the NXD1-derived factor required for neoxanthin synthesis takes place in the cytosol. Finally, we postulate that ABA4, with additional unknown cofactor(s), is required for, or contributes to, trans-to-cis violaxanthin isomerase activity, producing both cis-xanthophyll precursors of ABA.
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Claims 8
Claim · model-written summary
ABA4 is required for formation of trans- and 9′-cis-neoxanthin from trans-violaxanthin.
- Taxon
- Arabidopsis
Arabidopsise1 - Gene
- ABA4e0
- Compound
- trans-violaxanthine0
- Outcome
- formation of trans- and 9′-cis-neoxanthine0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“ABA4 is not only required for the formation of trans- and 9′-cis-neoxanthin from trans-violaxanthin”
e1“in Arabidopsis”
Claim · model-written summary
ABA4 controls 9-cis-violaxanthin accumulation.
- Taxon
- ArabidopsisArabidopsise1
- Gene
- ABA4e0
- Outcome
- 9-cis-violaxanthin accumulatione0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“ABA4 is not only required for the formation of trans- and 9′-cis-neoxanthin from trans-violaxanthin, but also controls 9-cis-violaxanthin accumulation”
e1“in Arabidopsis”
Claim · model-written summary
The aba4 nxd1 mutant has reduced 9-cis-violaxanthin in leaves and seeds relative to nxd1.
- Taxon
- ArabidopsisArabidopsise1
- Material
- aba4 nxd1e0
- Organ / stage
- leaves and seedse0
- Outcome
- 9-cis-violaxanthine0
- Direction
- reducede0
- Comparator
- nxd1e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“While nxd1 produces high amounts of 9-cis-violaxanthin and ABA, aba4 nxd1 exhibits reduced levels in both leaves and seeds”
e1“in Arabidopsis”
Claim · model-written summary
The aba4 nxd1 mutant has reduced ABA in leaves and seeds relative to nxd1.
- Taxon
- ArabidopsisArabidopsise1
- Material
- aba4 nxd1e0
- Organ / stage
- leaves and seedse0
- Outcome
- ABAe0
- Direction
- reducede0
- Comparator
- nxd1e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“While nxd1 produces high amounts of 9-cis-violaxanthin and ABA, aba4 nxd1 exhibits reduced levels in both leaves and seeds”
e1“in Arabidopsis”
Claim · model-written summary
Constitutive ABA4 expression in nxd1 increases 9-cis-violaxanthin accumulation.
- Taxon
- ArabidopsisArabidopsise1
- Material
- nxd1e0
- Treatment
- ABA4 constitutive expressione0
- Gene
- ABA4e0
- Outcome
- 9-cis-violaxanthine0
- Direction
- increasese0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“ABA4 constitutive expression in nxd1 increases both 9-cis-violaxanthin and ABA accumulation”
e1“in Arabidopsis”
Claim · model-written summary
Constitutive ABA4 expression in nxd1 increases ABA accumulation.
- Taxon
- ArabidopsisArabidopsise1
- Material
- nxd1e0
- Treatment
- ABA4 constitutive expressione0
- Gene
- ABA4e0
- Outcome
- ABA accumulatione0
- Direction
- increasese0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“ABA4 constitutive expression in nxd1 increases both 9-cis-violaxanthin and ABA accumulation”
e1“in Arabidopsis”
Claim · model-written summary
Transient NXD1 localization suggests production of the neoxanthin synthesis factor in the cytosol.
- Taxon
- ArabidopsisArabidopsise1
- Gene
- NXD1e0
- Outcome
- production of the NXD1-derived factor required for neoxanthin synthesis takes place in the cytosole0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Subcellular localization of NXD1 protein in transient expression assays suggests that production of the NXD1-derived factor required for neoxanthin synthesis takes place in the cytosol”
e1“in Arabidopsis”
Claim · model-written summary
The authors postulate that ABA4 and unknown cofactors contribute to trans-to-cis violaxanthin isomerase activity.
- Taxon
- ArabidopsisArabidopsise1
- Gene
- ABA4e0
- Outcome
- trans-to-cis violaxanthin isomerase activitye0
- Qualifier
- additional unknown cofactor(s)e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“we postulate that ABA4, with additional unknown cofactor(s), is required for, or contributes to, trans-to-cis violaxanthin isomerase activity, producing both cis-xanthophyll precursors of ABA”
e1“in Arabidopsis”
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