title: Characterization of the genes encoding the cytosolic and plastidial forms of ADP-glucose pyrophosphorylase in wheat endosperm.
abstract: In most species, the synthesis of ADP-glucose (Glc) by the enzyme ADP-Glc pyrophosphorylase (AGPase) occurs entirely within the plastids in all tissues so far examined. However, in the endosperm of many, if not all grasses, a second form of AGPase synthesizes ADP-Glc outside the plastid, presumably in the cytosol. In this paper, we show that in the endosperm of wheat (Triticum aestivum), the cytosolic form accounts for most of the AGPase activity. Using a combination of molecular and biochemical approaches to identify the cytosolic and plastidial protein components of wheat endosperm AGPase we show that the large and small subunits of the cytosolic enzyme are encoded by genes previously thought to encode plastidial subunits, and that a gene, Ta.AGP.S.1, which encodes the small subunit of the cytosolic form of AGPase, also gives rise to a second transcript by the use of an alternate first exon. This second transcript encodes an AGPase small subunit with a transit peptide. However, we could not find a plastidial small subunit protein corresponding to this transcript. The protein sequence of the purified plastidial small subunit does not match precisely to that encoded by Ta.AGP.S.1 or to the predicted sequences of any other known gene from wheat or barley (Hordeum vulgare). Instead, the protein sequence is most similar to those of the plastidial small subunits from chickpea (Cicer arietinum) and maize (Zea mays) and rice (Oryza sativa) seeds. These data suggest that the gene encoding the major plastidial small subunit of AGPase in wheat endosperm has yet to be identified.
authors.affiliation: Department of Plant Science, University of Adelaide, Glen Osmond South Australia, Australia.
authors.forename: Rachel A
authors.initials: RA
authors.lastname: Burton
authors.forename: Philip E
authors.initials: PE
authors.lastname: Johnson
authors.forename: Diane M
authors.initials: DM
authors.lastname: Beckles
authors.forename: Geoffrey B
authors.initials: GB
authors.lastname: Fincher
authors.forename: Helen L
authors.initials: HL
authors.lastname: Jenner
authors.forename: Mike J
authors.initials: MJ
authors.lastname: Naldrett
authors.forename: Kay
authors.initials: K
authors.lastname: Denyer
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D002852:Chromatography, Ion Exchange; D003001:Cloning, Molecular; D003600:Cytosol / Q000201:enzymology*; D018076:DNA, Complementary / Q000737:chemistry / Q000235:genetics; D018744:DNA, Plant / Q000737:chemistry / Q000235:genetics; D018507:Gene Expression Regulation, Developmental / Q000235:genetics; D015971:Gene Expression Regulation, Enzymologic / Q000235:genetics; D018506:Gene Expression Regulation, Plant / Q000235:genetics; D051599:Glucose-1-Phosphate Adenylyltransferase; D008969:Molecular Sequence Data; D009713:Nucleotidyltransferases / Q000235:genetics* / Q000378:metabolism; D010802:Phylogeny; D018087:Plastids / Q000201:enzymology*; D012639:Seeds / Q000201:enzymology / Q000235:genetics* / Q000254:growth & development; D017422:Sequence Analysis, DNA; D020539:Sequence Analysis, Protein; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid; D014908:Triticum / Q000201:enzymology / Q000235:genetics* / Q000254:growth & development
chemical_list: D018076:DNA, Complementary; D018744:DNA, Plant; D009713:Nucleotidyltransferases; D051599:Glucose-1-Phosphate Adenylyltransferase