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  -