title: Mutants of Arabidopsis lacking a chloroplastic isoamylase accumulate phytoglycogen and an abnormal form of amylopectin.
abstract: Mutant lines defective for each of the four starch debranching enzyme (DBE) genes (AtISA1, AtISA2, AtISA3, and AtPU1) detected in the nuclear genome of Arabidopsis (Arabidopsis thaliana) were produced and analyzed. Our results indicate that both AtISA1 and AtISA2 are required for the production of a functional isoamylase-type of DBE named Iso1, the major isoamylase activity found in leaves. The absence of Iso1 leads to an 80% decrease in the starch content in both lines and to the accumulation of water-soluble polysaccharides whose structure is similar to glycogen. In addition, the residual amylopectin structure in the corresponding mutant lines displays a strong modification when compared to the wild type, suggesting a direct, rather than an indirect, function of Iso1 during the synthesis of amylopectin. Mutant lines carrying a defect in AtISA3 display a strong starch-excess phenotype at the end of both the light and the dark phases accompanied by a small modification of the amylopectin structure. This result suggests that this isoamylase-type of DBE plays a major role during starch mobilization. The analysis of the Atpu1 single-mutant lines did not lead to a distinctive phenotype. However, Atisa2/Atpu1 double-mutant lines display a 92% decrease in starch content. This suggests that the function of pullulanase partly overlaps that of Iso1, although its implication remains negligible when Iso1 is present within the cell.
authors.affiliation: Unité de Glycobiologie Structurale et Fonctionnelle, Université des Sciences et Technologies de Lille, 59655 Villeneuve d'Ascq cedex, France.
authors.forename: Fabrice
authors.initials: F
authors.lastname: Wattebled
authors.forename: Ying
authors.initials: Y
authors.lastname: Dong
authors.forename: Sylvain
authors.initials: S
authors.lastname: Dumez
authors.forename: David
authors.initials: D
authors.lastname: Delvallé
authors.forename: Véronique
authors.initials: V
authors.lastname: Planchot
authors.forename: Pierre
authors.initials: P
authors.lastname: Berbezy
authors.forename: Darshna
authors.initials: D
authors.lastname: Vyas
authors.forename: Paul
authors.initials: P
authors.lastname: Colonna
authors.forename: Manash
authors.initials: M
authors.lastname: Chatterjee
authors.forename: Steven
authors.initials: S
authors.lastname: Ball
authors.forename: Christophe
authors.initials: C
authors.lastname: D'Hulst
mesh_terms: D000681:Amylases / Q000172:deficiency*; D000687:Amylopectin / Q000235:genetics / Q000378:metabolism*; D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics*; D002736:Chloroplasts / Q000201:enzymology / Q000235:genetics*; D017343:Genes, Plant; D006003:Glycogen / Q000378:metabolism*; D016296:Mutagenesis; D012333:RNA, Messenger / Q000235:genetics; D018749:RNA, Plant / Q000235:genetics
chemical_list: D012333:RNA, Messenger; D018749:RNA, Plant; D006003:Glycogen; D000687:Amylopectin; D000681:Amylases