title: Loss of starch granule initiation has a deleterious effect on the growth of arabidopsis plants due to an accumulation of ADP-glucose.
abstract: STARCH SYNTHASE4 (SS4) is required for proper starch granule initiation in Arabidopsis (Arabidopsis thaliana), although SS3 can partially replace its function. Unlike other starch-deficient mutants, ss4 and ss3/ss4 mutants grow poorly even under long-day conditions. They have less chlorophyll and carotenoids than the wild type and lower maximal rates of photosynthesis. There is evidence of photooxidative damage of the photosynthetic apparatus in the mutants from chlorophyll a fluorescence parameters and their high levels of malondialdehyde. Metabolite profiling revealed that ss3/ss4 accumulates over 170 times more ADP-glucose (Glc) than wild-type plants. Restricting ADP-Glc synthesis, by introducing mutations in the plastidial phosphoglucomutase (pgm1) or the small subunit of ADP-Glc pyrophosphorylase (aps1), largely restored photosynthetic capacity and growth in pgm1/ss3/ss4 and aps1/ss3/ss4 triple mutants. It is proposed that the accumulation of ADP-Glc in the ss3/ss4 mutant sequesters a large part of the plastidial pools of adenine nucleotides, which limits photophosphorylation, leading to photooxidative stress, causing the chlorotic and stunted growth phenotypes of the plants.
authors.affiliation: Instituto de Bioquímica Vegetal y Fotosíntesis, Consejo Superior de Investigaciones Científicas-University of Sevilla, 41092 Seville, Spain.
authors.forename: Paula
authors.initials: P
authors.lastname: Ragel
authors.forename: Sebastian
authors.initials: S
authors.lastname: Streb
authors.forename: Regina
authors.initials: R
authors.lastname: Feil
authors.forename: Mariam
authors.initials: M
authors.lastname: Sahrawy
authors.forename: Maria Grazia
authors.initials: MG
authors.lastname: Annunziata
authors.forename: John E
authors.initials: JE
authors.lastname: Lunn
authors.forename: Samuel
authors.initials: S
authors.lastname: Zeeman
authors.forename: Ángel
authors.initials: Á
authors.lastname: Mérida
mesh_terms: D000245:Adenosine Diphosphate Glucose / Q000378:metabolism*; D017360:Arabidopsis / Q000254:growth & development* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics; D009154:Mutation; D018384:Oxidative Stress; D010766:Phosphorylation; D010788:Photosynthesis; D013213:Starch / Q000378:metabolism*; D013214:Starch Synthase / Q000235:genetics / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D000245:Adenosine Diphosphate Glucose; D013213:Starch; D013214:Starch Synthase