Note: a dashed line (without arrowheads) between two compound names is meant to imply that the two names are just different instantiations of the same compound -- i.e. one may be a specific name and the other a general name, or they may both represent the same compound in different stages of a polymerization-type pathway. If an enzyme name is shown in bold, there is experimental evidence for this enzymatic activity.
|Superclasses:||Biosynthesis → Carbohydrates Biosynthesis → Polysaccharides Biosynthesis → Glucogen and Starch Biosynthesis|
Some taxa known to possess this pathway include : Arabidopsis thaliana col [Delatte05], Chlamydomonas reinhardtii , Hordeum vulgare , Manihot esculenta , Nicotiana tabacum , Oryza sativa , Pisum sativum , Solanum tuberosum , Triticum aestivum , Zea mays
Starch and glycogen, megadalton-sized glucose polymers, are the major reservoir of readily available energy and carbon compounds in most living organisms, ranging from archaea, eubacteria and yeasts, up to higher eukaryotes including plants and animals [Zeeman10, Santelia11]. Only parasites seem to lack enzymes for the metabolism of these compounds [Henrissat02].
The structure of starch in higher plants differs from that of its counterpart a glycogen in animals and bacteria. Starch is a complex α-glucan that can be very difficult to adequately describe. Starch contains at least two different major sub-classes of α-glucans: amylose and amylopectin. Amylose contains up to several thousand α-glucosyl units linked almost exclusively in α(1->4) linkage with very few branches of α(1->6) linkage. Amylopectin, on the other hand is a much more branched molecule with many α(1->6) linkages and contains up to several million glucosyl residues. At least twelve different types of starch with different branching patterns and chain lengths have been reported [Robyt13]. To further complicate the situation, starch can appears in different crystalline and soluble forms which are difficult to define and depict using standard chemical structures.
It has been reported that cyanobacteria synthesize glycogen while red algae produce floridean-starch with structure that is intermediate between starch and glycogen, and that green algae accumulate amylopectin-like polysaccharides. However, some cyanobacteria have distinct α-polyglucans (which were designated as semi-amylopectin), making them a transition point between glycogen and starch biosynthesis [Nakamura05].
About This Pathway
Starch is synthesized in plastids, including chloroplasts in photosynthetic tissues and amyloplasts in non-photosynthetic tissues such as seeds, roots, and tubers. Starch synthesized in chloroplasts of photosynthetic tissues is degraded to maltose and glucose during the dark period (see starch degradation II). These sugars are exported to the cytosol and used in sucrose synthesis. Sucrose can be readily transported to non-photosynthetic tissues to support plant growth or for starch synthesis in amyloplasts.
The starch biosynthesis pathway depicted here includes both chloroplast and amyloplast pathways. The starting point for the chloroplast pathway is fructose-6-phosphate, a product of photosynthetic carbon fixation. The starting point for amyloplast pathway is glucose-1-phosphate, a product of sucrose degradation. Studies from potato, pea, and maize indicate that glucose-6-phosphate, in addition to glucose-1-phosphate, can be imported into the amyloplast and can serve as the starting point for starch biosynthesis [Tauberger00].
The role of plastidial α-phosphorylase enzymes (126.96.36.199) in starch biosynthesis remain controversial and may differ between species [Streb12, Ball09]. For example, mutations in the PHS1 gene of Arabidopsis have no effect on starch biosynthesis [Zeeman04].
Following the initial production of ADP-α-D-glucose, starch biosynthesis appears to involve reactions catalyzed by at least three classes of enzymes, i.e. starch synthases, starch branching enzymes and starch debranching enzymes [Ball09]. However, the exact steps involved and the order in which they are required for the formation of different types of starch may differ between species and even between different types of cells within the same species [Delatte05].
There is also evidence that Chlamydomonas reinhardtii might involve an additional enzyme in starch biosynthesis, namely, a disproportionating enzyme, DPE1. However the corresponding enzyme, DPE1 in Arabidopsis has been shown to play a part in starch degradation instead [Ball09, Streb12].
Developing a better understanding of starch biosynthesis and its regulation is an active area of research.
Ball09: Ball, Steven J., Deschamps, Philippe (2009). "Chapter 1: Starch Metabolism." The Chlamydomonas Sourcebook (Second Edition). Edited by: Elizabeth H. Harris, Ph.D., David B. Stern, Ph.D., and George B. Witman, Ph.D. Volume 2:1-40.
Delatte05: Delatte T, Trevisan M, Parker ML, Zeeman SC (2005). "Arabidopsis mutants Atisa1 and Atisa2 have identical phenotypes and lack the same multimeric isoamylase, which influences the branch point distribution of amylopectin during starch synthesis." Plant J 41(6);815-30. PMID: 15743447
Mouille96: Mouille G, Maddelein ML, Libessart N, Talaga P, Decq A, Delrue B, Ball S (1996). "Preamylopectin Processing: A Mandatory Step for Starch Biosynthesis in Plants." Plant Cell 8(8);1353-1366. PMID: 12239416
Nakamura05: Nakamura Y, Takahashi J, Sakurai A, Inaba Y, Suzuki E, Nihei S, Fujiwara S, Tsuzuki M, Miyashita H, Ikemoto H, Kawachi M, Sekiguchi H, Kurano N (2005). "Some Cyanobacteria synthesize semi-amylopectin type alpha-polyglucans instead of glycogen." Plant Cell Physiol 46(3);539-45. PMID: 15695453
Tauberger00: Tauberger E, Fernie AR, Emmermann M, Renz A, Kossmann J, Willmitzer L, Trethewey RN (2000). "Antisense inhibition of plastidial phosphoglucomutase provides compelling evidence that potato tuber amyloplasts import carbon from the cytosol in the form of glucose-6-phosphate." Plant J 2000;23(1);43-53. PMID: 10929100
Wattebled08: Wattebled F, Planchot V, Dong Y, Szydlowski N, Pontoire B, Devin A, Ball S, D'Hulst C (2008). "Further evidence for the mandatory nature of polysaccharide debranching for the aggregation of semicrystalline starch and for overlapping functions of debranching enzymes in Arabidopsis leaves." Plant Physiol 148(3);1309-23. PMID: 18815382
Zabawinski01: Zabawinski C, Van Den Koornhuyse N, D'Hulst C, Schlichting R, Giersch C, Delrue B, Lacroix JM, Preiss J, Ball S (2001). "Starchless mutants of Chlamydomonas reinhardtii lack the small subunit of a heterotetrameric ADP-glucose pyrophosphorylase." J Bacteriol 183(3);1069-77. PMID: 11208806
Zeeman04: Zeeman SC, Thorneycroft D, Schupp N, Chapple A, Weck M, Dunstan H, Haldimann P, Bechtold N, Smith AM, Smith SM (2004). "Plastidial alpha-glucan phosphorylase is not required for starch degradation in Arabidopsis leaves but has a role in the tolerance of abiotic stress." Plant Physiol 135(2);849-58. PMID: 15173560
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Baveja86: Baveja UK, Jyoti AS, Kaur M, Agarwal DS, Anand BS, Nanda R (1986). "Isoenzyme studies of Giardia lamblia isolated from symptomatic cases." Aust J Exp Biol Med Sci 64 ( Pt 2);119-26. PMID: 2943257
Buleon97: Buleon A, Gallant DJ, Bouchet B, Mouille G, D'Hulst C, Kossmann J, Ball S (1997). "Starches from A to C. Chlamydomonas reinhardtii as a model microbial system to investigate the biosynthesis of the plant amylopectin crystal." Plant Physiol 115(3);949-57. PMID: 9390431
Chae11: Chae, Lee (2011). "The functional annotation of protein sequences was performed by the in-house Ensemble Enzyme Prediction Pipeline (E2P2, version 1.0). E2P2 systematically integrates results from three molecular function annotation algorithms using an ensemble classification scheme. For a given genome, all protein sequences are submitted as individual queries against the base-level annotation methods. The individual methods rely on homology transfer to annotate protein sequences, using single sequence (BLAST, E-value cutoff <= 1e-30, subset of SwissProt 15.3) and multiple sequence (Priam, November 2010; CatFam, version 2.0, 1% FDR profile library) models of enzymatic functions. The base-level predictions are then integrated into a final set of annotations using an average weighted integration algorithm, where the weight of each prediction from each individual method was determined via a 0.632 bootstrap process over 1000 rounds of testing. The training and testing data for E2P2 and the BLAST reference database were drawn from protein sequences with experimental support of existence, compiled from SwissProt release 15.3."
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Dauvillee01: Dauvillee D, Colleoni C, Mouille G, Buleon A, Gallant DJ, Bouchet B, Morell MK, d'Hulst C, Myers AM, Ball SG (2001). "Two loci control phytoglycogen production in the monocellular green alga Chlamydomonas reinhardtii." Plant Physiol 125(4);1710-22. PMID: 11299352
Dauvillee01a: Dauvillee D, Colleoni C, Mouille G, Morell MK, d'Hulst C, Wattebled F, Lienard L, Delvalle D, Ral JP, Myers AM, Ball SG (2001). "Biochemical characterization of wild-type and mutant isoamylases of Chlamydomonas reinhardtii supports a function of the multimeric enzyme organization in amylopectin maturation." Plant Physiol 125(4);1723-31. PMID: 11299353
Delatte06: Delatte T, Umhang M, Trevisan M, Eicke S, Thorneycroft D, Smith SM, Zeeman SC (2006). "Evidence for distinct mechanisms of starch granule breakdown in plants." J Biol Chem 281(17);12050-9. PMID: 16495218
Delrue92: Delrue B, Fontaine T, Routier F, Decq A, Wieruszeski JM, Van Den Koornhuyse N, Maddelein ML, Fournet B, Ball S (1992). "Waxy Chlamydomonas reinhardtii: monocellular algal mutants defective in amylose biosynthesis and granule-bound starch synthase activity accumulate a structurally modified amylopectin." J Bacteriol 174(11);3612-20. PMID: 1592815
Delvalle05: Delvalle D, Dumez S, Wattebled F, Roldan I, Planchot V, Berbezy P, Colonna P, Vyas D, Chatterjee M, Ball S, Merida A, D'Hulst C (2005). "Soluble starch synthase I: a major determinant for the synthesis of amylopectin in Arabidopsis thaliana leaves." Plant J 43(3);398-412. PMID: 16045475
Dumez06: Dumez S, Wattebled F, Dauvillee D, Delvalle D, Planchot V, Ball SG, D'Hulst C (2006). "Mutants of Arabidopsis lacking starch branching enzyme II substitute plastidial starch synthesis by cytoplasmic maltose accumulation." Plant Cell 18(10);2694-709. PMID: 17028209
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