Enhancement of Plant Productivity by Manipulation of ADPglucose Pyrophosphorylase

Okita, Thomas W.; Nakata, Paul A.; Ball, Kathryn L.; Smith-White, Brian; Preiss, Jack

doi:10.1007/978-1-4899-1136-0_10

Cited by 11 publications

(15 citation statements)

References 71 publications

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“…These studies demonstrate direct causal relationships between decreased levels in gene products, of enzyme activities, and of starch levels, and therefore substantiate the view that ADPGlc pyrophosphorylase is absolutely required for starch synthesis. Therefore, one can conclude that, on the basis of the results of these studies (2,3,12,13,15,17), the ADPGlc used for starch synthesis is formed in the plastid via the activity of ADPGlc pyrophosphorylase and that the SS-ADPGlc pathway plays little, if any, role in this process.…”

Section: The Alternative Pathway Of Starch Synthesismentioning

confidence: 98%

“…The Arabidopsis mutants adgl and adg2 (12,17), the maize endosperm mutants sh2 and bt2 (3,15,17), the transgenic potato plants harboring antisense DNA constructs to an ADPGlc pyrophosphorylase gene (13), and a Chlamydomonas mutant (2) have depressed levels of starch and deficient levels of ADPGlc pyrophosphorylase activities due to specific losses of one or both of the ADPGlc pyrophosphorylase subunits or reduction in allosteric activation by 3-PGA. Likewise, a direct correlation was also observed between the levels of starch and ADPGlc pyrophosphorylase enzyme activity and not between starch and sucrose synthase activity in the pea embryo mutant rb (18).…”

Section: The Alternative Pathway Of Starch Synthesismentioning

confidence: 99%

“…Recent studies have shown that the allosterically regulated ADPGlc2 pyrophosphorylase, as well other enzymes involved in starch synthesis, are localized in the amyloplasts (1, 10, l 2 Abbreviations: ADPGlc, ADPglucose; 3-PGA, D-glycerate 3-phosphate; PGI, phosphoglucoisomerase; PGM, phosphoglucomutase; SS-ADPGlc, sucrose synthase-dependent synthesis of ADPGlc; UDPGlc, UDPglucose; Glc 1-P, glucose 1-phosphate; Glc 6-P, glucose 6-phosphate. 15,17), indicating that the basic enzymology of starch synthesis is the same in amyloplasts as in chloroplasts. The flow of carbon and the exchange of metabolites between the amyloplast and cytosol in developing sink organs, however, are not identical to the processes established for leaves (1,6,7,9,17,19).…”

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confidence: 99%

“…Maize mutations at two unlinked loci, Shrunken-2 (Sh2) and Brittle-2 (Bt2), result in a 60% reduction in starch levels in the endosperm with corresponding decreases in ADPGlc pyrophosphorylase activities of 66% and 63%, respectively (17). Recent biochemical and molecular studies (3,15,17) have shown that Sh2 and Bt2 encode ADPGlc pyrophosphorylase subunits of 54 kD and 51 kD, respectively, and that both subunits are required for maximum enzyme activity and starch synthesis.…”

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Is There an Alternative Pathway for Starch Synthesis?

Okita¹

1992

Plant Physiol.

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133

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In leaf tissue, carbon enters starch via the gluconeogenesis pathway where D-glycerate 3-phosphate formed from CO2 fixation is converted into hexose monophosphates within the chloroplast stroma. In starch-containing sink organs, evidence has been obtained indicating that the flow of carbon into starch follows a different pathway whereby hexose monophosphates formed from sucrose are transported into the amyloplast, a plastid specialized in starch accumulation. In both chloroplasts and amyloplasts, the formation of ADPglucose, the substrate for starch synthase, is controlled by the activity of ADPglucose pyrophosphorylase, a key regulatory enzyme of starch synthesis localized in the plastid. Recently, an alternative pathway of starch synthesis has been proposed in which ADPglucose is synthesized from sucrose and transported directly into the plastid compartment, where it is used for starch synthesis. On the basis of the biochemical phenotypes exhibited by various plant mutants with defined genetic lesions, it is concluded that ADPglucose pyrophosphorylase is essential for starch synthesis, whereas the alternative pathway has only a minor role in this process.

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Section: The Alternative Pathway Of Starch Synthesismentioning

confidence: 98%

Section: The Alternative Pathway Of Starch Synthesismentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Is There an Alternative Pathway for Starch Synthesis?

Okita¹

1992

Plant Physiol.

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133

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“…AGP catalyzes the initial, allosterically regulated reaction in starch biosynthesis in both photosynthetic and nonphotosynthetic tissues and provides a pivotal point at which manipulation of this pathway can take place (Kleczkowski et al, 1991;Okita et al, 1993;Nakata and Okita, 1994). Before we can fully manipulate this enzyme and starch biosynthesis, we must begin to understand how AGP interacts with its substrates and effectors.…”

Section: Discussionmentioning

confidence: 99%

Aspartic Acid 413 Is Important for the Normal Allosteric Functioning of ADP-Glucose Pyrophosphorylase

1996

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As part of a structure-function analysis of the higher-plant ADP-glucose pyrophosphorylase (AGP), we used a random mutagenesis approach in combination with a novel bacterial complementation system to isolate over 100 mutants that were defective in glycogen production (T.W. Greene, S.E. Chantler, M.L. Khan, G.F. Barry, J. Preiss, T.W. Okita [1996] Proc Natl Acad Sci USA 93: 1509–1513). One mutant of the large subunit M27 was identified by its capacity to only partially complement a mutation in the structural gene for the bacterial AGP (glg C), as determined by its light-staining phenotype when cells were exposed to I2 vapors. Enzyme-linked immunosorbent assay and enzymatic pyrophosphorylysis assays of M27 cell extracts showed that the level of expression and AGP activity was comparable to those of cells that expressed the wild-type recombinant enzyme. Kinetic analysis indicated that the M27 AGP displays normal Michaelis constant values for the substrates glucose-1-phosphate and ATP but requires 6- to 10-fold greater levels of 3-phosphoglycerate (3-PGA) than the wild-type recombinant enzyme for maximum activation. DNA sequence analysis showed that M27 contains a single point mutation that resulted in the replacement of aspartic acid 413 to alanine. Substitution of a lysine residue at this site almost completely abolished activation by 3-PGA. Aspartic acid 413 is adjacent to a lysine residue that was previously identified by chemical modification studies to be important in the binding of 3-PGA (K. Ball, J. Preiss [1994] J Biol Chem 269: 24706–24711). The kinetic properties of M27 corroborate the importance of this region in the allosteric regulation of a higher-plant AGP.

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Cis-elements important for the expression of the ADP-glucose pyrophosphorylase small-subunit are located both upstream and downstream from its structural gene

Nakata

Okita

1996

Molec. Gen. Genet.

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ADP-glucose pyrophosphorylase (AGP) is a key regulatory enzyme in the biosynthesis of starch in higher plants. Previous studies have suggested that, unlike other plants that display tissue-specific AGP genes, potato expresses the same AGP small-subunit gene (sAGP) in multiple tissues. This view was confirmed by the spatial patterns of expression of the sAGP gene in transgenic potato plants observed when a promoter-dependent-beta-glucuronidase (beta-GUS) system was used. sAGP-beta-GUS chimeric gene fusions were expressed at high levels in tubers and in many other starch-containing cells throughout the plant. Deletional analysis of the 5'-upstream region of sAGP revealed that the observed spatial patterns of expression were due to different regions of the promoter of sAGP functioning in combination to confer cell- and organ-specific patterns of expression. Depending on the tissue examined, the patterns of reporter-gene expression were enhanced, suppressed, or altered when the 3'-nopaline-synthase terminator was replaced by the 3'-flanking sequence of sAGP. The observed cellular expression patterns of sAGP only partially overlap with the reported expression patterns of the major large-subunit gene (lAGP) in leaves. Since AGP is a heterotetrameric enzyme, composed of two sAGP and two lAGP subunits, this difference in the cellular expression patterns as well as quantitative differences in expression of the two AGP genes may account for the observed post-transcriptional regulation, i.e., relatively high levels of transcript but low levels of sAGP subunit in leaves.

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Enhancement of Plant Productivity by Manipulation of ADPglucose Pyrophosphorylase

Cited by 11 publications

References 71 publications

Is There an Alternative Pathway for Starch Synthesis?

Is There an Alternative Pathway for Starch Synthesis?

Aspartic Acid 413 Is Important for the Normal Allosteric Functioning of ADP-Glucose Pyrophosphorylase

Cis-elements important for the expression of the ADP-glucose pyrophosphorylase small-subunit are located both upstream and downstream from its structural gene

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