title: Double knockout mutants of Arabidopsis grown under normal conditions reveal that the plastidial phosphorylase isozyme participates in transitory starch metabolism.
abstract: In leaves of two starch-related single-knockout lines lacking either the cytosolic transglucosidase (also designated as disproportionating enzyme 2, DPE2) or the maltose transporter (MEX1), the activity of the plastidial phosphorylase isozyme (PHS1) is increased. In both mutants, metabolism of starch-derived maltose is impaired but inhibition is effective at different subcellular sites. Two constitutive double knockout mutants were generated (designated as dpe2-1×phs1a and mex1×phs1b) both lacking functional PHS1. They reveal that in normally grown plants, the plastidial phosphorylase isozyme participates in transitory starch degradation and that the central carbon metabolism is closely integrated into the entire cell biology. All plants were grown either under continuous illumination or in a light-dark regime. Both double mutants were compromised in growth and, compared with the single knockout plants, possess less average leaf starch when grown in a light-dark regime. Starch and chlorophyll contents decline with leaf age. As revealed by transmission electron microscopy, mesophyll cells degrade chloroplasts, but degradation is not observed in plants grown under continuous illumination. The two double mutants possess similar but not identical phenotypes. When grown in a light-dark regime, mesophyll chloroplasts of dpe2-1×phs1a contain a single starch granule but under continuous illumination more granules per chloroplast are formed. The other double mutant synthesizes more granules under either growth condition. In continuous light, growth of both double mutants is similar to that of the parental single knockout lines. Metabolite profiles and oligoglucan patterns differ largely in the two double mutants.
authors.affiliation: Institute of Biochemistry and Biology, Department of Plant Physiology , University of Potsdam, Karl-Liebknecht-Strasse 24-25, Building 20, 14476 Potsdam-Golm, Germany.
authors.forename: Irina
authors.initials: I
authors.lastname: Malinova
authors.forename: Sebastian
authors.initials: S
authors.lastname: Mahlow
authors.forename: Saleh
authors.initials: S
authors.lastname: Alseekh
authors.forename: Tom
authors.initials: T
authors.lastname: Orawetz
authors.forename: Alisdair R
authors.initials: AR
authors.lastname: Fernie
authors.forename: Otto
authors.initials: O
authors.lastname: Baumann
authors.forename: Martin
authors.initials: M
authors.lastname: Steup
authors.forename: Joerg
authors.initials: J
authors.lastname: Fettke
mesh_terms: D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics / Q000254:growth & development* / Q000648:ultrastructure; D029681:Arabidopsis Proteins / Q000378:metabolism*; D018533:Biomass; D050260:Carbohydrate Metabolism; D002244:Carbon / Q000378:metabolism; D002734:Chlorophyll / Q000378:metabolism; D002846:Chromatography, Affinity; D003433:Crosses, Genetic; D055786:Gene Knockout Techniques; D006004:Glycogen Debranching Enzyme System / Q000378:metabolism*; D007527:Isoenzymes / Q000378:metabolism; D008320:Maltose / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000378:metabolism; D058503:Mesophyll Cells / Q000378:metabolism / Q000648:ultrastructure; D055432:Metabolomics; D009154:Mutation / Q000235:genetics*; D010641:Phenotype; D017440:Photoperiod; D018087:Plastids / Q000201:enzymology* / Q000648:ultrastructure; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism*; D013213:Starch / Q000378:metabolism*; D013395:Sucrose / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; C000592241:DPE2 protein, Arabidopsis; D006004:Glycogen Debranching Enzyme System; D007527:Isoenzymes; C000590716:MEX1 protein, Arabidopsis; D026901:Membrane Transport Proteins; D002734:Chlorophyll; D013395:Sucrose; D008320:Maltose; D002244:Carbon; D013213:Starch; C514675:PHS1 protein, Arabidopsis; D017027:Protein Tyrosine Phosphatases