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  - Koetting, Oliver
A1  - Santelia, Diana
A1  - Edner, Christoph
A1  - Eicke, Simona
A1  - Marthaler, Tina
A1  - Gentry, Matthew S.
A1  - Comparot-Moss, Sylviane
A1  - Chen, Jychian
A1  - Smith, Alison M.
A1  - Steup, Martin
A1  - Ritte, Gerhard
A1  - Zeeman, Samuel C.
T1  - STARCH-EXCESS4 is a laforin-like phosphoglucan phosphatase required for starch degradation in Arabidopsis thaliana
N2  - Starch is the major storage carbohydrate in plants. It is comprised of glucans that form semicrystalline granules. Glucan phosphorylation is a prerequisite for normal starch breakdown, but phosphoglucan metabolism is not understood. A putative protein phosphatase encoded at the Starch Excess 4 (SEX4) locus of Arabidopsis thaliana was recently shown to be required for normal starch breakdown. Here, we show that SEX4 is a phosphoglucan phosphatase in vivo and define its role within the starch degradation pathway. SEX4 dephosphorylates both the starch granule surface and soluble phosphoglucans in vitro, and sex4 null mutants accumulate phosphorylated intermediates of starch breakdown. These compounds are linear alpha-1,4-glucans esterified with one or two phosphate groups. They are released from starch granules by the glucan hydrolases alpha-amylase and isoamylase. In vitro experiments show that the rate of starch granule degradation is increased upon simultaneous phosphorylation and dephosphorylation of starch. We propose that glucan phosphorylating enzymes and phosphoglucan phosphatases work in synergy with glucan hydrolases to mediate efficient starch catabolism.
Y1  - 2009
UR  - http://www.plantcell.org/
U6  - https://doi.org/10.1105/tpc.108.064360
SN  - 1040-4651
ER  - 
TY  - JOUR
A1  - Yu, Tien-Shin
A1  - Kofler, Heike
A1  - Häusler, Rainer E.
A1  - Hille, Diana
A1  - Flügge, Ulf-Ingo
A1  - Zeeman, Samuel C.
A1  - Smith, Alison M.
A1  - Kossmann, Jens
A1  - Lloyd, James R.
A1  - Ritte, Gerhard
A1  - Steup, Martin
A1  - Lue, Wei-Ling
A1  - Chen, Jychian
A1  - Weber, Andreas P. M.
T1  - The Arabidopsis sex1 mutant is defective in the R1 protein, a general regulator of starch degradation in plants, and not in the chloroplast hexose transporter
Y1  - 2001
SN  - 1040-4651
ER  -