title: Integrated functions among multiple starch synthases determine both amylopectin chain length and branch linkage location in Arabidopsis leaf starch.
abstract: This study assessed the impact on starch metabolism in Arabidopsis leaves of simultaneously eliminating multiple soluble starch synthases (SS) from among SS1, SS2, and SS3. Double mutant ss1- ss2- or ss1- ss3- lines were generated using confirmed null mutations. These were compared to the wild type, each single mutant, and ss1- ss2- ss3- triple mutant lines grown in standardized environments. Double mutant plants developed similarly to the wild type, although they accumulated less leaf starch in both short-day and long-day diurnal cycles. Despite the reduced levels in the double mutants, lines containing only SS2 and SS4, or SS3 and SS4, are able to produce substantial amounts of starch granules. In both double mutants the residual starch was structurally modified including higher ratios of amylose:amylopectin, altered glucan chain length distribution within amylopectin, abnormal granule morphology, and altered placement of α(1→6) branch linkages relative to the reducing end of each linear chain. The data demonstrate that SS activity affects not only chain elongation but also the net result of branch placement accomplished by the balanced activities of starch branching enzymes and starch debranching enzymes. SS3 was shown partially to overlap in function with SS1 for the generation of short glucan chains within amylopectin. Compensatory functions that, in some instances, allow continued residual starch production in the absence of specific SS classes were identified, probaby accomplished by the granule bound starch synthase GBSS1.
authors.affiliation: Unité de Glycobiologie Structurale et Fonctionnelle, UMR8576 CNRS-Université Lille 1, sciences et technologies, F-59655 Villeneuve d'Ascq, France.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Szydlowski
authors.forename: Paula
authors.initials: P
authors.lastname: Ragel
authors.forename: Tracie A
authors.initials: TA
authors.lastname: Hennen-Bierwagen
authors.forename: Véronique
authors.initials: V
authors.lastname: Planchot
authors.forename: Alan M
authors.initials: AM
authors.lastname: Myers
authors.forename: Angel
authors.initials: A
authors.lastname: Mérida
authors.forename: Christophe
authors.initials: C
authors.lastname: d'Hulst
authors.forename: Fabrice
authors.initials: F
authors.lastname: Wattebled
mesh_terms: D000687:Amylopectin / Q000737:chemistry* / Q000378:metabolism* / Q000648:ultrastructure; D000688:Amylose / Q000378:metabolism; D017360:Arabidopsis / Q000201:enzymology*; D005591:Chemical Fractionation; D002850:Chromatography, Gel; D009154:Mutation / Q000235:genetics; D010936:Plant Extracts / Q000378:metabolism; D018515:Plant Leaves / Q000378:metabolism*; D012995:Solubility; D013214:Starch Synthase / Q000378:metabolism*
chemical_list: D010936:Plant Extracts; D000688:Amylose; D000687:Amylopectin; D013214:Starch Synthase