Abstract
Enzymological and starch analyses of various ADP-glucose pyrophosphorylase (AGPase) null mutants point to fundamental differences in the pathways for starch synthesis in the maize leaf, embryo, ovary and endosperm. Leaf starch is synthesized via the AGPase encoded by the small and large subunits shown previously to be expressed at abundant levels in the leaf, whereas more than one AGPase isoform functions in the embryo and in the ovary. Embryo starch content is also dependent on genes functioning in the leaf and in the endosperm. AGPase encoded by shrunken-2 and brittle-2 synthesizes ~75% of endosperm starch. The gene, agpsemzm, previously shown to encode the small subunit expressed in the embryo, and agpllzm, the leaf large subunit gene, are here shown to encode the endosperm, plastid-localized AGPase. Loss of this enzyme does not reduce endosperm starch. Rather, the data suggest that AGPase-independent starch synthesis accounts for ~25% of endosperm starch. Three maize genes encode the small subunit of the AGPase. Data here show that the triple mutant lacking all three small subunits is lethal in early seed development but can be viable in both male and female gametes. Seed and plant viability is restored by any one of the three small subunit genes, including one previously thought to function only in the cytosol of the endosperm. Data herein also show the functionality of a fourth gene encoding the large subunit of this enzyme. Although adenosine diphosphate glucose pyrophosphorylase is shown here to be essential for maize viability, strong evidence for starch synthesis in the endosperm that is independent of this enzyme is also presented. Starch synthesis is distinct in the maize embryo, ovary, leaf and endosperm, and is coordinated among the various tissues.
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Claims 14
Claim · model-written summary
Leaf starch synthesis uses AGPase encoded by leaf-expressed subunits.
Zea maysOrganisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Leaf starch is synthesized via the AGPase encoded by the small and large subunits shown previously to be expressed at abundant levels in the leaf”
t0“maize”
Claim · model-written summary
Multiple AGPase isoforms function in embryo and ovary.
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“more than one AGPase isoform functions in the embryo and in the ovary”
t0“maize”
Claim · model-written summary
Embryo starch content depends on genes active in leaf and endosperm.
- Organ / stage
- Embryoe0
- Gene
- genes functioning in the leaf and in the endosperme0
- Outcome
- Embryo starch contente0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Embryo starch content is also dependent on genes functioning in the leaf and in the endosperm.”
t0“maize”
Claim · model-written summary
Shrunken-2 and brittle-2 AGPase synthesizes about 75% of endosperm starch.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“AGPase encoded by shrunken-2 and brittle-2 synthesizes ~75% of endosperm starch.”
t0“maize”
Claim · model-written summary
agpsemzm and agpllzm encode plastid-localized endosperm AGPase.
- Organ / stage
- endosperme0
- Gene
- agpsemzme0
- Outcome
- endosperm, plastid-localized AGPasee0
- Qualifier
- agpllzme0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“agpsemzm, previously shown to encode the small subunit expressed in the embryo, and agpllzm, the leaf large subunit gene, are here shown to encode the endosperm, plastid-localized AGPase.”
t0“maize”
Claim · model-written summary
Loss of plastid-localized AGPase does not reduce endosperm starch.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Loss of this enzyme does not reduce endosperm starch.”
e1“endosperm, plastid-localized AGPase”
t0“maize”
Claim · model-written summary
The data suggest AGPase-independent synthesis supplies about 25% of endosperm starch.
- Organ / stage
- endosperme0
- Gene
- AGPasee0
- Outcome
- endosperm starche0
- Value
- ~25%e0
- Qualifier
- AGPase-independent starch synthesise0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the data suggest that AGPase-independent starch synthesis accounts for ~25% of endosperm starch.”
t0“maize”
Claim · model-written summary
Three maize genes encode the AGPase small subunit.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Three maize genes encode the small subunit of the AGPase.”
Claim · model-written summary
The triple small-subunit mutant is lethal in early seed development.
- Material
- triple mutante0
- Organ / stage
- early seed developmente0
- Outcome
- lethal in early seed developmente0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the triple mutant lacking all three small subunits is lethal in early seed development”
e1“Three maize genes”
Claim · model-written summary
The triple mutant is viable in male and female gametes.
- Material
- triple mutante1
- Organ / stage
- male and female gametese0
- Outcome
- viable in both male and female gametese0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“can be viable in both male and female gametes”
e1“the triple mutant lacking all three small subunits”
e2“Three maize genes”
Claim · model-written summary
Any one of the three small-subunit genes restores seed and plant viability.
- Treatment
- any one of the three small subunit genese0
- Outcome
- Seed and plant viabilitye0
- Direction
- restorede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Seed and plant viability is restored by any one of the three small subunit genes”
e1“Three maize genes”
Claim · model-written summary
A fourth large-subunit gene is functional.
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Data herein also show the functionality of a fourth gene encoding the large subunit of this enzyme.”
e1“Three maize genes”
Claim · model-written summary
AGPase is essential for maize viability.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“adenosine diphosphate glucose pyrophosphorylase is shown here to be essential for maize viability”
Claim · model-written summary
Starch synthesis differs and is coordinated across maize embryo, ovary, leaf and endosperm.
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Starch synthesis is distinct in the maize embryo, ovary, leaf and endosperm, and is coordinated among the various tissues.”