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Ranunculus ficaria
Starch Biosynthesis and Improved Starch Production
Starch Biosynthesis and Improved starch production
1.1 Properties of starch
1.2 Carbon flow during starch synthesis
1.2.1 Enzymes and intermediates
1.2.2 Regulation of starch synthesis and of amylose/amylopectin ratio
1. Starch
2. Improved starch production
Glycogen
- All animals (e.g. human liver) many microbes
- Carbohydrate storage
- Highly branched (high solubility)
- UDPGluc serves as activated sugar
- Glycogenine (protein, that (auto)catalyzes a first Glc moiety from UDPGlc to Tyr194)
- Next reaction catalyzed by Glycogen Synthase)
UDP-Glc + Tyr194-Glc
UDP + Tyr194-Glc-Glc
Glycogen Synthase is covalently modified
GS + ATP GS-P + ADP aktiv inaktiv
Starch is closely related to glycogen
Glycogen Synthase
Starch: different sources, different applications
assembled (zusammengesetzt) starch
Starch kernels appear in individual shapes
reducing end
Amylopectin: 500000 - mill Glc units
every 15 - 30 α1.4-linkage one additional α1.6-linkage
Starch consists of two types of molecules: amylose and amylopectin
Amylose: 3-7000 Glc units, form α-helical structure (6 Glc residues per loop)
Amylose is α-helical organized
Starch test: J2 is de facto a proof for amylose not for starch in total
starch free zones cor-respond to chlorophyll free zones
Spherical structure of starch is determined by amylopectin
amorphous lamellae of loose branching
crystalline lamellae of dense helical arrangement
mut
Wt
Starch metabolism must be regulated !
Characteristics of starch less mutants 1. increased shoot/root ratio
2. low tolerance against drought stress
3. grow only at optimal nutrient conditions
4. increased respiration
5. normal phenotype under permanent light
starch less
wild type
starch less wild type
In some algae starch synthesis takes place outside the plastid
nucleo- morph
- schematic -
Starch
nucleus
periplastidial space
plastid
pyrenoid
cER
cytosol
-TEM -
pps
starch
Guillardia theta
Guillardia starch kernels show a unique shape (inner cavity)
Starch biosynthesis starts with hexose phosphates
AGPGlc pyrophophorylase (AGPase) is the “rate limiting” step
- rate limiting step
- immediate hydrolysis of PPi - in plants heterotetramer
2 α-UE (50 kDa), 2 β-UE (53 kDA)
- allosteric effectors Pi und 3-PGA
- 3-PGA/Pi ratio is critical for resulting V
+ -
Three levels of AGPase regulation
- +
Starch synthases produce the glucose polymer
in addition: individual RNA processing and first evidence for post-transcriptional modification by phosphorylation leads to individual starch synthase enzymes
two isoenzymes of Starch Synthases: soluble Starch Synthase SSS granula-bound Starch Synthase GBSS SSS: amylopectin synthesis (high substrate affinity) GBSS: amylose synthesis (low affinity, located on and in kernels)
We always find isoforms of Starch Synthases !
Intra-transfer (within a chain) Inter-transfer (two chains involved)
OH
OH
OH OH OH
OH
OH
Residual segment
Acceptor-chain
Donor-chain
Branching Enzymes produce α1.6-linkages
OH
Branching Enzymes
Start
We keep in mind:
Starch-free mutants show substantial developmental defects
Starch consists of amylose and amylopectin; in higher plants always in plastids
AGPase is regulated allosterically and by covalent modification. 3-PGA is activator; Pi acts as an inhibitor. Reduced thioredoxin activates AGPase in addition (AGPasered). High cellular sugar levels promote expression of AGPase genes
Regulation of starch biosynthesis occurs on the level of ADPGlucose Pyrophosphorylase (rate limiting step)
Improved Starch Metabolism in Higher Plants
ADP
Mitochondrion Amyloplast
starch fatty acids
2 x
ATP ATP
ADP ADP
Tjaden et al., 1998a; Trentmann et al., 2000
Nucleotide transport in potato tuber cells
Adenosine triphosphate (ATP)
Nucleotide transport
DNA / RNA Enzyme cofactors
Second Messenger Precursors for hormones
universial energy currency
Nucleotides, the most important metabolites on earth !?
TWINLAB
80 mg/day 30 kg/day
demand
Nucleotides, the most important metabolites on earth !?
Starch synthesis in potato tubers
ATP ATP
STARCH
ADPGlc
Glc1P
Glc6P
AGPase ATP
ADP
ATP ADP
Pi
potato amyloplast
Glc6P
x
ginger-like morphology
budding tubers
high sugar, low starch content iodide staining
first step of starch synthesis
Wild type NTT antisense
NTT activity is crucial for starch biosynthesis; but does it limit starch levels ?
WT NTT antisense lines
Tjaden et al., 1998 Plant J. 16
Tubers from antisense lines destain easily after iodine treatment, WT tubers do not!
Wild type NTT antisense
Iodine staining
Wild type NTT antisense
line1 NTT antisense
line1
Iodine de-staining
30 min, hot water triiodite captured in amylose
Tjaden et al., 1998 Plant J. 16
Amylose structure
Amylose, α-1.4 linked, linear glucose polymer
- Up to 1000 glc units/molecule
Amylopectin structure
Amylopectin
Amylopectin, α-1.4 and α-1.6 branched glucose polymer
- every 15-30 α-1.4 linkages a branch at position 1.6, up to 105 glc units
Carbon pathway into the two products: amylose and amylopectin
GBSS, sticks to starch granule surface
SSS, soluble in stroma
low ADPGlc affinity !
high ADPGlc affinity !
Antisense lines show low starch, low amylose but high sugar levels Tjaden et al., 1998 Plant J. 16
triiodite captured in amylose
first step of starch synthesis
Glc1P ADPGlc
ATPATP
STARCH
ADPGlc
Glc1P
Glc6P
AGPase ATP
ADP
ATP ADP
Pi
potato amyloplast
Glc6P
Can we increase starch production by increased provision of Glc6P or ATP
GPT2 mRNA NTT mRNA
Overexpression of GPT or NTT alone does not improve potato starch levels
Zhang et al. 2006, Plant Biotech. J. 6
NTT mRNA on basis of GPT
overexpressors
Simultaneous Overexpression of GPT or NTT improve potato starch levels
Zhang et al. 2006, Plant Biotech. J. 6
Zhang et al. 2006, Plant Biotech. J. 6
As a consequence, overexpressors contain more amylose
How to produce very-high amylose potatoes ?
GBSS, sticks to starch corn surface
SSS, soluble in stroma
Western-blot analysis revealed massively reduced SBE-A and SBE-B levels
Schwall et al, 2000, Nat.Biotech. 18
Production of very-high-amylose potato starch by inhibition of SBE A and B
Schwall et al, 2000, Nat.Biotech. 18
Production of very-high-amylose potato starch by inhibition of SBE A and B
no change in total yield
Hofander et al, 2004 Plant Biotech. J. 2
Wt SBE antisense
Production of very-high-amylose potato starch by inhibition of SBE A and B
polarized light
Schwall et al, 2000, Nat.Biotech. 18
Hofander et al, 2004 Plant Biotech. J. 2
Wt SBE antisense
iodine staining
iodine trapped in amylose
Carbon pathway into the two products: Amylose and Amylopectin
GBSS, sticks to starch corn surface
SSS, soluble in stroma
Visser et al. 1991 Mol. Gen. Genet. 225
Production of very-high-amylopectin potato starch (AMFLORA®) by inhibition of GBSS
AMFLORA®, BASF potato
WT GBSS antisense
WT
GBSS antisense
No staining by iodine demonstrates absence of amylose !
Visser et al. 1991 Mol. Gen. Genet. 225
Production of very-high-amylopectin potato starch by inhibition of GBSS
low GBSS activity correlates with almost complete absence of amylose !
high GBSS activity correlates with high amylose contents!
GBSS, Western-blot analysis
wild type maize low starch, brittle1 mutation
Brittle1, a member of the mitochondrial carrier family (MCF)
brittle: dürr, brüchig
Starch synthesis in monocotyledonous endosperm tissue
ADPGlc ADPGlc
STARCH
Brittle-1
cytosol
amyloplast
Zmbt1 Glc1P
AGPase
Kirchberger et al. (2007) J. Biol. Chem. 282
Effector (5x) ZmBT1
ADPG uptake
none 100 ATP 71 ADP 15
ADP-Glc 24
AMP 82
ADPGlc
ADP
antiport
ZmBt1 transports ADPGlc in an antiport mode with ADP
% of control
monocot´s possess brittle1 proteins for import of ADPGlc into the amyloplast
!
! !
Kirchberger et al. (2007) J. Biol. Chem. 282
Starch synthesis in dicot´s and monocot´s (cereals) differs
Brittle-1
ADPGlc ADPGlc
STARCH
ADP ADP
monocotyledonous amyloplast
Glc1P
AGPase
ATP ATP
STARCH
ADPGlc
Glc1P
Glc6P
AGPase ATP
ADP
ATP ADP
Pi
dicotyledonous amyloplast
Glc6P
Improvement of starch levels in maize Wang et al., 2007, Plant Cell Tissue Cult. 88, 83-92
Expression of a bacterial (E.coli) AGPase (glgC16) in maize
AGPase, ADP glucose pyrophosphorylase
Improvement of starch levels in maize. glgC16 is not Pi inhibited! Wang et al., 2007, Plant Cell Tissue Cult. 88, 83-92
The bacterial (E.coli) AGPase (glgC16) is not phosphate inhibited AGPase
AGPase, ADP glucose pyrophosphorylase
Pi
Wt AGPase inhibition by Pi
Improvement of starch levels in maize. Correlation AGPase activity/seed weight Wang et al., 2007, Plant Cell Tissue Cult. 88, 83-92
Wt seed weight