Abstract
We recently discovered that post-translational redox modulation of ADP-glucose pyrophosphorylase (AGPase) is a powerful new mechanism to adjust the rate of starch synthesis to the availability of sucrose in growing potato tubers. A strong correlation was observed between the endogenous levels of sucrose and the redox-activation state of AGPase. To identify candidate components linking AGPase redox modulation to sugar supply, we used potato tuber discs as a model system. When the discs were cut from growing wild-type potato tubers and incubated for 2 h in the absence of sugars, redox activation of AGPase decreased because of a decrease in internal sugar levels. The decrease in AGPase redox activation could be prevented when glucose or sucrose was supplied to the discs. Both sucrose uptake and redox activation of AGPase were increased when EDTA was used to prepare the tuber discs. However, EDTA treatment of discs had no effect on glucose uptake. Feeding of different glucose analogues revealed that the phosphorylation of hexoses by hexokinase is an essential component in the glucose-dependent redox activation of AGPase. In contrast to this, feeding of the non-metabolisable sucrose analogue, palatinose, leads to a similar activation as with sucrose, indicating that metabolism of sucrose is not necessary in the sucrose-dependent AGPase activation. The influence of sucrose and glucose on redox activation of AGPase was also investigated in discs cut from tubers of antisense plants with reduced SNF1-related protein kinase activity (SnRK1). Feeding of sucrose to tuber discs prevented AGPase redox inactivation in the wild type but not in SnRK1 antisense lines. However, feeding of glucose leads to a similar activation of AGPase in the wild type and in SnRK1 transformants. AGPase redox activation was also increased in transgenic tubers with ectopic overexpression of invertase, containing high levels of glucose and low sucrose levels. Expression of a bacterial glucokinase in the invertase-expressing background led to a decrease in AGPase activation state and tuber starch content. These results show that both sucrose and glucose lead to post-translational redox activation of AGPase, and that they do this by two different pathways involving SnRK1 and an endogenous hexokinase, respectively.
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Claims 13
Claim · model-written summary
Endogenous sucrose levels strongly correlated with AGPase redox activation.
- Taxon
- potato
Solanum tuberosumt0 - Gene
- AGPasee0
- Compound
- sucrosee0
- Outcome
- redox-activation state of AGPasee0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“potato tubers”
e0“A strong correlation was observed between the endogenous levels of sucrose and the redox-activation state of AGPase.”
Claim · model-written summary
Sugar-free incubation decreased AGPase redox activation in wild-type potato tuber discs.
- Taxon
- potatoSolanum tuberosume0
- Material
- wild-typee0
- Organ / stage
- tuberse0
- Treatment
- incubated for 2 h in the absence of sugarse0
- Gene
- AGPasee0
- Outcome
- redox activation of AGPasee0
- Direction
- decreasede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“When the discs were cut from growing wild-type potato tubers and incubated for 2 h in the absence of sugars, redox activation of AGPase decreased because of a decrease in internal sugar levels.”
Claim · model-written summary
Glucose supply prevented the decrease in AGPase redox activation.
- Taxon
- potatoSolanum tuberosumt0
- Treatment
- glucosee0
- Gene
- AGPasee0
- Outcome
- AGPase redox activatione0
- Direction
- preventede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“potato tubers”
e0“The decrease in AGPase redox activation could be prevented when glucose or sucrose was supplied to the discs.”
Claim · model-written summary
Sucrose supply prevented the decrease in AGPase redox activation.
- Taxon
- potatoSolanum tuberosumt0
- Treatment
- sucrosee0
- Gene
- AGPasee0
- Outcome
- AGPase redox activatione0
- Direction
- preventede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“potato tubers”
e0“The decrease in AGPase redox activation could be prevented when glucose or sucrose was supplied to the discs.”
Claim · model-written summary
EDTA preparation increased sucrose uptake and AGPase redox activation.
- Taxon
- potatoSolanum tuberosumt0
- Treatment
- EDTAe0
- Gene
- AGPasee0
- Outcome
- sucrose uptake and redox activation of AGPasee0
- Direction
- increasede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“potato tubers”
e0“Both sucrose uptake and redox activation of AGPase were increased when EDTA was used to prepare the tuber discs.”
Claim · model-written summary
EDTA preparation had no effect on glucose uptake.
- Taxon
- potatoSolanum tuberosumt0
- Treatment
- EDTA treatmente0
- Outcome
- glucose uptakee0
- Direction
- no effecte0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“potato tubers”
e0“EDTA treatment of discs had no effect on glucose uptake.”
Claim · model-written summary
Hexokinase phosphorylation of hexoses was essential for glucose-dependent AGPase activation.
- Taxon
- potatoSolanum tuberosumt0
- Gene
- hexokinasee0
- Outcome
- glucose-dependent redox activation of AGPasee0
- Qualifier
- phosphorylation of hexosese0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“potato tubers”
e0“the phosphorylation of hexoses by hexokinase is an essential component in the glucose-dependent redox activation of AGPase.”
Claim · model-written summary
Palatinose activated AGPase similarly to sucrose.
- Taxon
- potatoSolanum tuberosumt0
- Treatment
- palatinosee0
- Outcome
- activatione0
- Direction
- similare0
- Comparator
- sucrosee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“potato tubers”
e0“feeding of the non-metabolisable sucrose analogue, palatinose, leads to a similar activation as with sucrose”
Claim · model-written summary
Sucrose feeding prevented AGPase inactivation in wild-type but not SnRK1 antisense tuber discs.
- Taxon
- potatoSolanum tuberosumt0
- Treatment
- Feeding of sucrosee0
- Gene
- SnRK1e0
- Outcome
- AGPase redox inactivatione0
- Direction
- preventede0
- Comparator
- SnRK1 antisense linese0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“potato tubers”
e0“Feeding of sucrose to tuber discs prevented AGPase redox inactivation in the wild type but not in SnRK1 antisense lines.”
Claim · model-written summary
Glucose feeding activated AGPase similarly in wild type and SnRK1 transformants.
- Taxon
- potatoSolanum tuberosumt0
- Treatment
- feeding of glucosee0
- Gene
- AGPasee0
- Outcome
- activation of AGPasee0
- Direction
- similare0
- Comparator
- SnRK1 transformantse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“potato tubers”
e0“feeding of glucose leads to a similar activation of AGPase in the wild type and in SnRK1 transformants.”
Claim · model-written summary
Invertase overexpression increased AGPase redox activation in transgenic tubers.
- Taxon
- potatoSolanum tuberosumt0
- Treatment
- ectopic overexpression of invertasee0
- Gene
- invertasee0
- Outcome
- AGPase redox activatione0
- Direction
- increasede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“potato tubers”
e0“AGPase redox activation was also increased in transgenic tubers with ectopic overexpression of invertase, containing high levels of glucose and low sucrose levels.”
Claim · model-written summary
Bacterial glucokinase expression in the invertase background decreased AGPase activation.
- Taxon
- potatoSolanum tuberosumt0
- Treatment
- Expression of a bacterial glucokinasee0
- Gene
- bacterial glucokinasee0
- Outcome
- AGPase activation statee0
- Direction
- decreasee0
- Comparator
- invertase-expressing backgrounde0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“potato tubers”
e0“Expression of a bacterial glucokinase in the invertase-expressing background led to a decrease in AGPase activation state and tuber starch content.”
Claim · model-written summary
Bacterial glucokinase expression in the invertase background decreased tuber starch content.
- Taxon
- potatoSolanum tuberosumt0
- Treatment
- Expression of a bacterial glucokinasee0
- Outcome
- tuber starch contente0
- Direction
- decreasee0
- Comparator
- invertase-expressing backgrounde0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“potato tubers”
e0“Expression of a bacterial glucokinase in the invertase-expressing background led to a decrease in AGPase activation state and tuber starch content.”
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