TY - JOUR A1 - Comparot-Moss, Sylviane A1 - Koetting, Oliver A1 - Stettler, Michaela A1 - Edner, Christoph A1 - Graf, Alexander A1 - Weise, Sean E. A1 - Streb, Sebastian A1 - Lue, Wei-Ling A1 - MacLean, Daniel A1 - Mahlow, Sebastian A1 - Ritte, Gerhard A1 - Steup, Martin A1 - Chen, Jychian A1 - Zeeman, Samuel C. A1 - Smith, Alison M. T1 - A putative phosphatase, LSF1, is required for normal starch turnover in Arabidopsis leaves N2 - A putative phosphatase, LSF1 (for LIKE SEX4; previously PTPKIS2), is closely related in sequence and structure to STARCH-EXCESS4 (SEX4), an enzyme necessary for the removal of phosphate groups from starch polymers during starch degradation in Arabidopsis (Arabidopsis thaliana) leaves at night. We show that LSF1 is also required for starch degradation: lsf1 mutants, like sex4 mutants, have substantially more starch in their leaves than wild-type plants throughout the diurnal cycle. LSF1 is chloroplastic and is located on the surface of starch granules. lsf1 and sex4 mutants show similar, extensive changes relative to wild-type plants in the expression of sugar-sensitive genes. However, although LSF1 and SEX4 are probably both involved in the early stages of starch degradation, we show that LSF1 neither catalyzes the same reaction as SEX4 nor mediates a sequential step in the pathway. Evidence includes the contents and metabolism of phosphorylated glucans in the single mutants. The sex4 mutant accumulates soluble phospho- oligosaccharides undetectable in wild-type plants and is deficient in a starch granule-dephosphorylating activity present in wild-type plants. The lsf1 mutant displays neither of these phenotypes. The phenotype of the lsf1/sex4 double mutant also differs from that of both single mutants in several respects. We discuss the possible role of the LSF1 protein in starch degradation. Y1 - 2010 UR - http://www.plantphysiol.org/ U6 - https://doi.org/10.1104/pp.109.148981 SN - 0032-0889 ER - TY - JOUR A1 - Fettke, Jörg A1 - Albrecht, Tanja A1 - Hejazi, Mahdi A1 - Mahlow, Sebastian A1 - Nakamura, Yasunori A1 - Steup, Martin T1 - Glucose 1-phosphate is efficiently taken up by potato (Solanum tuberosum) tuber parenchyma cells and converted to reserve starch granules N2 - Reserve starch is an important plant product but the actual biosynthetic process is not yet fully understood. Potato (Solanum tuberosum) tuber discs from various transgenic plants were used to analyse the conversion of external sugars or sugar derivatives to starch. By using in vitro assays, a direct glucosyl transfer from glucose 1-phosphate to native starch granules as mediated by recombinant plastidial phosphorylase was analysed. Compared with labelled glucose, glucose 6-phosphate or sucrose, tuber discs converted externally supplied [C-14] glucose 1-phosphate into starch at a much higher rate. Likewise, tuber discs from transgenic lines with a strongly reduced expression of cytosolic phosphoglucomutase, phosphorylase or transglucosidase converted glucose 1-phosphate to starch with the same or even an increased rate compared with the wild-type. Similar results were obtained with transgenic potato lines possessing a strongly reduced activity of both the cytosolic and the plastidial phosphoglucomutase. Starch labelling was, however, significantly diminished in transgenic lines, with a reduced concentration of the plastidial phosphorylase isozymes. Two distinct paths of reserve starch biosynthesis are proposed that explain, at a biochemical level, the phenotype of several transgenic plant lines. Y1 - 2010 UR - http://www3.interscience.wiley.com/cgi-bin/issn?DESCRIPTOR=PRINTISSN&VALUE=0028-646X U6 - https://doi.org/10.1111/j.1469-8137.2009.03126.x SN - 0028-646X ER - TY - JOUR A1 - Hejazi, Mahdi A1 - Fettke, Jörg A1 - Koetting, Oliver A1 - Zeeman, Samuel C. A1 - Steup, Martin T1 - The Laforin-like dual-specificity phosphatase SEX4 from Arabidopsis hydrolyzes both C6-and C3-phosphate esters introduced by starch-related dikinases and thereby affects phase transition of alpha-glucans N2 - The biochemical function of the Laforin-like dual-specific phosphatase AtSEX4 (EC 3.1.3.48) has been studied. Crystalline maltodextrins representing the A- or the B-type allomorph were prephosphorylated using recombinant glucan, water dikinase (StGWD) or the successive action of both plastidial dikinases (StGWD and AtPWD). AtSEX4 hydrolyzed carbon 6-phosphate esters from both the prephosphorylated A- and B-type allomorphs and the kinetic constants are similar. The phosphatase also acted on prelabeled carbon-3 esters from both crystalline maltodextrins. Similarly, native starch granules prelabeled in either the carbon-6 or carbon-3 position were also dephosphorylated by AtSEX4. The phosphatase did also hydrolyze phosphate esters of both prephosphorylated maltodextrins when the (phospho)glucans had been solubilized by heat treatment. Submillimolar concentrations of nonphosphorylated maltodextrins inhibited AtSEX4 provided they possessed a minimum of length and had been solubilized. As opposed to the soluble phosphomaltodextrins, the AtSEX4- mediated dephosphorylation of the insoluble substrates was incomplete and at least 50% of the phosphate esters were retained in the pelletable (phospho) glucans. The partial dephosphorylation of the insoluble glucans also strongly reduced the release of nonphosphorylated chains into solution. Presumably, this effect reflects fast structural changes that following dephosphorylation occur near the surface of the maltodextrin particles. A model is proposed defining distinct stages within the phosphorylation/dephosphorylation-dependent transition of alpha-glucans from the insoluble to the soluble state. Y1 - 2010 UR - http://www.plantphysiol.org/ U6 - https://doi.org/10.1104/pp.109.149914 SN - 0032-0889 ER - TY - JOUR A1 - Steinfath, Matthias A1 - Strehmel, Nadine A1 - Peters, Rolf A1 - Schauer, Nicolas A1 - Groth, Detlef A1 - Hummel, Jan A1 - Steup, Martin A1 - Selbig, Joachim A1 - Kopka, Joachim A1 - Geigenberger, Peter A1 - Dongen, Joost T. van T1 - Discovering plant metabolic biomarkers for phenotype prediction using an untargeted approach N2 - Biomarkers are used to predict phenotypical properties before these features become apparent and, therefore, are valuable tools for both fundamental and applied research. Diagnostic biomarkers have been discovered in medicine many decades ago and are now commonly applied. While this is routine in the field of medicine, it is of surprise that in agriculture this approach has never been investigated. Up to now, the prediction of phenotypes in plants was based on growing plants and assaying the organs of interest in a time intensive process. For the first time, we demonstrate in this study the application of metabolomics to predict agronomic important phenotypes of a crop plant that was grown in different environments. Our procedure consists of established techniques to screen untargeted for a large amount of metabolites in parallel, in combination with machine learning methods. By using this combination of metabolomics and biomathematical tools metabolites were identified that can be used as biomarkers to improve the prediction of traits. The predictive metabolites can be selected and used subsequently to develop fast, targeted and low-cost diagnostic biomarker assays that can be implemented in breeding programs or quality assessment analysis. The identified metabolic biomarkers allow for the prediction of crop product quality. Furthermore, marker-assisted selection can benefit from the discovery of metabolic biomarkers when other molecular markers come to its limitation. The described marker selection method was developed for potato tubers, but is generally applicable to any crop and trait as it functions independently of genomic information. Y1 - 2010 UR - http://www3.interscience.wiley.com/cgi-bin/issn?DESCRIPTOR=PRINTISSN&VALUE=1467-7644 U6 - https://doi.org/10.1111/j.1467-7652.2010.00516.x SN - 1467-7644 ER -