Plastidial Localization of a Potato ‘Nudix ’ Hydrolase of ADP-glucose Linked to Starch Biosynthesis

Escherichia coli and potato (Solanum tuberosum) ADP-sugar pyrophosphatases (EcASPP and StASPP, respectively) are ‘Nudix ’ hydrolases of the bacterial glycogen and starch precursor molecule, ADP-glucose (ADPG). We have previously shown that potato leaves expressing EcASPP either in the cytosol or in the chloroplast exhibited large reductions in the levels of starch, suggesting the occurrence of cytosolic and plastidial pools of ADPG linked to starch biosynthesis. In this work, we produced and char-acterized potato and Arabidopsis plants expressing EcASPP and StASPP fused with green fluorescent protein (GFP). Confocal fluorescence microscopy analyses of these plants confirmed that EcASPP–GFP has a cytosolic localization, whereas StASPP–GFP occurs in the plastid stroma. Both source leaves and potato tubers from EcASPP–GFP