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Plant and Cell Physiology Advance Access published online on June 13, 2006
Plant and Cell Physiology, doi:10.1093/pcp/pcj065
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Plant and Cell Physiology 2006 © The Japanese Society of Plant Physiologists (JSPP); all rights reserved.
Received April 6, 2006
Accepted May 19, 2006

Regular Paper

Cloning, Expression and Characterization of a Nudix Hydrolase that Catalyzes the Hydrolytic Breakdown of ADP-Glucose Linked to Starch Biosynthesis in Arabidopsis thaliana

Francisco José Muñoz 1 *, Edurne Baroja-Fernández 1, María Teresa Morán-Zorzano 1, Nora Alonso-Casajús 1, and Javier Pozueta-Romero 1

1 Instituto de Agrobiotecnología, Universidad Pública de Navarra/Consejo Superior de Investigaciones Científicas/Gobierno de Navarra, Ctra. Mutilva s/n, 31192 Mutilva Baja, Navarra, Spain

* To whom correspondence should be addressed.
Francisco José Muñoz, E-mail: francisco.munoz{at}unavarra.es


  Abstract

"Nudix" hydrolases are widely distributed nucleotide pyrophosphatases that possess a conserved GX5EX7REUXEEXGU motif where U is usually Ile, Leu or Val. Among them, Escherichia coli ADP-sugar pyrophosphatase (ASPP) has been shown to catalyze the hydrolytic breakdown of ADP-glucose linked to bacterial glycogen biosynthesis (Moreno-Bruna et al. 2001). Comparisons of the 31 different Nudix encoding sequences of the Arabidopsis genome with those coding for known bacterial and mammalian ASPPs identified one sequence possessing important divergences in the Nudix motif that, once expressed in E. coli, produced a protein with ASPP activity. This protein, designated as AtASPP, shares strong homology with hypothetical rice and potato proteins, indicating that ASPPs are widely distributed in both mono- and di-cotyledonous plants. As a first step to test the possible involvement of plant ASPPs in regulating the intracellular levels of ADP-glucose linked to starch biosynthesis we produced and characterized AtASPP-overexpressing Arabidopsis plants. Source leaves from these plants exhibited a large reduction of the levels of both ADP-glucose and starch indicating that plant ASPPs catalyze the hydrolytic breakdown of a sizable pool of ADP-glucose linked to starch biosynthesis. No pleiotropic changes in maximum catalytic activities of enzymes closely linked to starch metabolism could be detected in AtASPP-overexpressing leaves. The overall informations provide a first evidence for the occurrence of plant Nudix hydrolases that have access to an intracellular pool of ADP-glucose linked to starch biosynthesis.

Keywords: Arabidopsis thaliana; Carbohydrate metabolism; Nudix hydrolase; Solanum tuberosum; Starch.
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