title: Enhancing sucrose synthase activity results in increased levels of starch and ADP-glucose in maize (Zea mays L.) seed endosperms.
abstract: Sucrose synthase (SuSy) is a highly regulated cytosolic enzyme that catalyzes the conversion of sucrose and a nucleoside diphosphate into the corresponding nucleoside diphosphate glucose and fructose. In cereal endosperms, it is widely assumed that the stepwise reactions of SuSy, UDPglucose pyrophosphorylase and ADPglucose (ADPG) pyrophosphorylase (AGP) take place in the cytosol to convert sucrose into ADPG necessary for starch biosynthesis, although it has also been suggested that SuSy may participate in the direct conversion of sucrose into ADPG. In this study, the levels of the major primary carbon metabolites, and the activities of starch metabolism-related enzymes were assessed in endosperms of transgenic maize plants ectopically expressing StSUS4, which encodes a potato SuSy isoform. A total of 29 fertile lines transformed with StSUS4 were obtained, five of them containing a single copy of the transgene that was still functional after five generations. The number of seeds per ear of the five transgenic lines containing a single StSUS4 copy was comparable with that of wild-type (WT) control seeds. However, transgenic seeds accumulated 10-15% more starch at the mature stage, and contained a higher amylose/amylopectin balance than WT seeds. Endosperms of developing StSUS4-expressing seeds exhibited a significant increase in SuSy activity, and in starch and ADPG contents when compared with WT endosperms. No significant changes could be detected in the transgenic seeds in the content of soluble sugars, and in activities of starch metabolism-related enzymes when compared with WT seeds. A suggested metabolic model is presented wherein both AGP and SuSy are involved in the production of ADPG linked to starch biosynthesis in maize endosperm cells.
authors.affiliation: Instituto de Agrobiotecnología, Universidad Pública de Navarra/Consejo Superior de Investigaciones Científicas/Gobierno de Navarra, Mutiloako etorbidea zenbaki gabe, 31192 Mutiloabeti, Nafarroa, Spain.
authors.forename: Jun
authors.initials: J
authors.lastname: Li
authors.forename: Edurne
authors.initials: E
authors.lastname: Baroja-Fernández
authors.forename: Abdellatif
authors.initials: A
authors.lastname: Bahaji
authors.forename: Francisco José
authors.initials: FJ
authors.lastname: Muñoz
authors.forename: Miroslav
authors.initials: M
authors.lastname: Ovecka
authors.forename: Manuel
authors.initials: M
authors.lastname: Montero
authors.forename: María Teresa
authors.initials: MT
authors.lastname: Sesma
authors.forename: Nora
authors.initials: N
authors.lastname: Alonso-Casajús
authors.forename: Goizeder
authors.initials: G
authors.lastname: Almagro
authors.forename: Angela María
authors.initials: AM
authors.lastname: Sánchez-López
authors.forename: Maite
authors.initials: M
authors.lastname: Hidalgo
authors.forename: Marta
authors.initials: M
authors.lastname: Zamarbide
authors.forename: Javier
authors.initials: J
authors.lastname: Pozueta-Romero
mesh_terms: D000245:Adenosine Diphosphate Glucose / Q000378:metabolism*; D000687:Amylopectin / Q000378:metabolism; D000688:Amylose / Q000378:metabolism*; D056625:Endosperm / Q000201:enzymology* / Q000235:genetics; D004789:Enzyme Activation; D057075:Enzyme Assays; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D005964:Glucosyltransferases / Q000378:metabolism*; D008954:Models, Biological; D010084:Oxidation-Reduction; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified / Q000378:metabolism; D012995:Solubility; D005957:UTP-Glucose-1-Phosphate Uridylyltransferase / Q000378:metabolism; D003313:Zea mays / Q000201:enzymology* / Q000235:genetics
chemical_list: D010940:Plant Proteins; D000245:Adenosine Diphosphate Glucose; D000688:Amylose; D000687:Amylopectin; D005964:Glucosyltransferases; C022699:sucrose synthase; D005957:UTP-Glucose-1-Phosphate Uridylyltransferase