Abstract
To investigate the contribution of farnesyl diphosphate synthase (FPS) to the overall control of the mevalonic acid pathway in plants, we have generated transgenic Arabidopsis thaliana overexpressing the Arabidopsis FPS1S isoform. Despite high levels of FPS activity in transgenic plants (8- to 12-fold as compared to wild-type plants), the content of sterols and the levels of 3-hydroxy-3-methylglutaryl-CoA reductase activity in leaves were similar to those in control plants. Plants overexpressing FPS1S showed a cell death/senescence-like phenotype and grew less vigorously than wild-type plants. The onset and the severity of these phenotypes directly correlated with the levels of FPS activity. In leaves of plants with increased FPS activity, the expression of the senescence activated gene SAG12 was prematurely induced. Transgenic plants grown in the presence of either mevalonic acid (MVA) or the cytokinin 2-isopentenyladenine (2-iP) recovered the wild-type phenotype. Quantification of endogenous cytokinins demonstrated that FPS1S overexpression specifically reduces the levels of endogenous zeatin-type cytokinins in leaves. Altogether these results support the notion that increasing FPS activity without a concomitant increase of MVA production leads to a reduction of IPP and DMAPP available for cytokinin biosynthesis. The reduced cytokinin levels would be, at least in part, responsible for the phenotypic alterations observed in the transgenic plants. The finding that wild-type and transgenic plants accumulated similar increased amounts of sterols when grown in the presence of exogenous MVA suggests that FPS1S is not limiting for sterol biosynthesis.
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Claims 12
Claim · model-written summary
FPS1S transgenic plants had FPS activity 8 to 12 times that of wild type.
- Treatment
- transgenic plantse0
- Outcome
- FPS activitye0
- Direction
- high levelse0
- Value
- 8- to 12-folde0
- Comparator
- wild-type plantse0
Not reportedTaxon
Verbatim
e0“high levels of FPS activity in transgenic plants (8- to 12-fold as compared to wild-type plants)”
Claim · model-written summary
Sterol content and HMG-CoA reductase activity were similar in transgenic and control leaves.
- Outcome
- the content of sterols and the levels of 3-hydroxy-3-methylglutaryl-CoA reductase activitye0
- Direction
- similare0
- Comparator
- control plantse0
Not reportedTaxonTreatment
Verbatim
e0“the content of sterols and the levels of 3-hydroxy-3-methylglutaryl-CoA reductase activity in leaves were similar to those in control plants.”
Claim · model-written summary
FPS1S overexpressors showed cell death or senescence-like symptoms and less vigorous growth than wild type.
- Treatment
- overexpressing FPS1Se0
- Gene
- FPS1Se0
- Outcome
- cell death/senescence-like phenotype and grew less vigorouslye0
- Direction
- less vigorouslye0
- Comparator
- wild-type plantse0
Not reportedTaxon
Verbatim
e0“Plants overexpressing FPS1S showed a cell death/senescence-like phenotype and grew less vigorously than wild-type plants.”
Claim · model-written summary
Onset and severity of overexpression phenotypes correlated with FPS activity.
Not reportedTaxon
Verbatim
e0“The onset and the severity of these phenotypes directly correlated with the levels of FPS activity.”
Claim · model-written summary
SAG12 expression was induced prematurely in leaves with increased FPS activity.
- Organ / stage
- leavese0
- Gene
- SAG12e0
- Outcome
- expression of the senescence activated gene SAG12e0
- Direction
- prematurely inducede0
Not reportedTaxon
Verbatim
e0“In leaves of plants with increased FPS activity, the expression of the senescence activated gene SAG12 was prematurely induced.”
Claim · model-written summary
Mevalonic acid restored the wild-type phenotype in FPS1S transgenic plants.
Not reportedTaxonComparator
Verbatim
e0“Transgenic plants grown in the presence of either mevalonic acid (MVA) or the cytokinin 2-isopentenyladenine (2-iP) recovered the wild-type phenotype.”
Claim · model-written summary
2-isopentenyladenine restored the wild-type phenotype in FPS1S transgenic plants.
Not reportedTaxonComparator
Verbatim
e0“Transgenic plants grown in the presence of either mevalonic acid (MVA) or the cytokinin 2-isopentenyladenine (2-iP) recovered the wild-type phenotype.”
Claim · model-written summary
FPS1S overexpression reduced endogenous zeatin-type cytokinins in leaves.
- Organ / stage
- leavese0
- Treatment
- FPS1S overexpressione0
- Outcome
- levels of endogenous zeatin-type cytokininse0
- Direction
- reducese0
Not reportedTaxonComparator
Verbatim
e0“FPS1S overexpression specifically reduces the levels of endogenous zeatin-type cytokinins in leaves.”
Claim · model-written summary
Increased FPS activity without increased MVA production may reduce IPP and DMAPP for cytokinin biosynthesis.
- Gene
- FPSe0
- Outcome
- IPP and DMAPP available for cytokinin biosynthesise0
- Qualifier
- without a concomitant increase of MVA productione0
Not reportedTaxon
Verbatim
e0“increasing FPS activity without a concomitant increase of MVA production leads to a reduction of IPP and DMAPP available for cytokinin biosynthesis.”
Claim · model-written summary
Reduced cytokinin levels may partly explain the phenotypic alterations of transgenic plants.
Not reportedTaxon
Verbatim
e0“The reduced cytokinin levels would be, at least in part, responsible for the phenotypic alterations observed in the transgenic plants.”
Claim · model-written summary
Exogenous MVA raised sterol accumulation similarly in wild type and transgenic plants.
- Treatment
- exogenous MVAe0
- Outcome
- amounts of sterolse0
- Direction
- similar increasede0
- Comparator
- wild-typee0
Not reportedTaxon
Verbatim
e0“wild-type and transgenic plants accumulated similar increased amounts of sterols when grown in the presence of exogenous MVA”
Claim · model-written summary
FPS1S does not appear to limit sterol biosynthesis.
Not reportedTaxon
Verbatim
e0“FPS1S is not limiting for sterol biosynthesis.”