Journal Article

Enhancing Sucrose Synthase Activity Results in Increased Levels of Starch and ADP-Glucose in Maize (<i>Zea mays</i> L.) Seed Endosperms

Jun Li, Edurne Baroja-Fernández, Abdellatif Bahaji, Francisco José Muñoz, Miroslav Ovecka, Manuel Montero, María Teresa Sesma, Nora Alonso-Casajús, Goizeder Almagro, Angela María Sánchez-López, Maite Hidalgo, Marta Zamarbide and Javier Pozueta-Romero

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 54, issue 2, pages 282-294
Published in print February 2013 | ISSN: 0032-0781
Published online January 2013 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pcs180
Enhancing Sucrose Synthase Activity Results in Increased Levels of Starch and ADP-Glucose in Maize (Zea mays L.) Seed Endosperms

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  • Biochemistry
  • Molecular and Cell Biology
  • Plant Sciences and Forestry

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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.

Keywords: Carbohydrate metabolism; Endosperm; Maize; Starch; Sucrose synthase

Journal Article.  6793 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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