title: Arabidopsis thaliana mutants lacking ADP-glucose pyrophosphorylase accumulate starch and wild-type ADP-glucose content: further evidence for the occurrence of important sources, other than ADP-glucose pyrophosphorylase, of ADP-glucose linked to leaf starch biosynthesis.
abstract: It is widely considered that ADP-glucose pyrophosphorylase (AGP) is the sole source of ADP-glucose linked to bacterial glycogen and plant starch biosynthesis. Genetic evidence that bacterial glycogen biosynthesis occurs solely by the AGP pathway has been obtained with glgC⁻ AGP mutants. However, recent studies have shown that (i) these mutants can accumulate high levels of ADP-glucose and glycogen, and (ii) there are sources other than GlgC, of ADP-glucose linked to glycogen biosynthesis. In Arabidopsis, evidence showing that starch biosynthesis occurs solely by the AGP pathway has been obtained with the starchless adg1-1 and aps1 AGP mutants. However, mounting evidence has been compiled previewing the occurrence of more than one important ADP-glucose source in plants. In attempting to solve this 20-year-old controversy, in this work we carried out a judicious characterization of both adg1-1 and aps1. Both mutants accumulated wild-type (WT) ADP-glucose and approximately 2% of WT starch, as further confirmed by confocal fluorescence microscopic observation of iodine-stained leaves and of leaves expressing granule-bound starch synthase fused with GFP. Introduction of the sex1 mutation affecting starch breakdown into adg1-1 and aps1 increased the starch content to 8-10% of the WT starch. Furthermore, aps1 leaves exposed to microbial volatiles for 10 h accumulated approximately 60% of the WT starch. aps1 plants expressing the bacterial ADP-glucose hydrolase EcASPP in the plastid accumulated normal ADP-glucose and reduced starch when compared with aps1 plants, whereas aps1 plants expressing EcASPP in the cytosol showed reduced ADP-glucose and starch. Moreover, aps1 plants expressing bacterial AGP in the plastid accumulated WT starch and ADP-glucose. The overall data show that (i) there occur important source(s), other than AGP, of ADP-glucose linked to starch biosynthesis, and (ii) AGP is a major determinant of starch accumulation but not of intracellular ADP-glucose content in Arabidopsis.
authors.affiliation: Instituto de Agrobiotecnología, Universidad Pública de Navarra/Consejo Superior de Investigaciones Científicas/Gobierno de Navarra, Mutiloako Etorbidea Zenbaki Gabe, 31192 Mutiloabeti, Nafarroa, Spain.
authors.forename: Abdellatif
authors.initials: A
authors.lastname: Bahaji
authors.forename: Jun
authors.initials: J
authors.lastname: Li
authors.forename: Miroslav
authors.initials: M
authors.lastname: Ovecka
authors.forename: Ignacio
authors.initials: I
authors.lastname: Ezquer
authors.forename: Francisco J
authors.initials: FJ
authors.lastname: Muñoz
authors.forename: Edurne
authors.initials: E
authors.lastname: Baroja-Fernández
authors.forename: Jose M
authors.initials: JM
authors.lastname: Romero
authors.forename: Goizeder
authors.initials: G
authors.lastname: Almagro
authors.forename: Manuel
authors.initials: M
authors.lastname: Montero
authors.forename: Maite
authors.initials: M
authors.lastname: Hidalgo
authors.forename: María T
authors.initials: MT
authors.lastname: Sesma
authors.forename: Javier
authors.initials: J
authors.lastname: Pozueta-Romero
mesh_terms: D000245:Adenosine Diphosphate Glucose / Q000096:biosynthesis*; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D051599:Glucose-1-Phosphate Adenylyltransferase / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D018515:Plant Leaves / Q000378:metabolism; D030821:Plants, Genetically Modified / Q000201:enzymology / Q000235:genetics; D013213:Starch / Q000096:biosynthesis*; D013214:Starch Synthase / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D000245:Adenosine Diphosphate Glucose; D013213:Starch; D013214:Starch Synthase; D051599:Glucose-1-Phosphate Adenylyltransferase