Functional Analysis Of A Wheat AGPase Plastidial Small Subunit With A Truncated Transit Peptide For Starch Synthesis

ADP-glucose pyrophosphorylase(AGPase),the key enzyme in starch synthesis,consists of two small subunits and two large subunits with cytosolic and plastidial isoforms.In our previous study,a c DNA sequence encoding the plastidial small subunit(Ta AGPS1b)of AGPase in grains of bread wheat(Triticum aestivum L.)was isolated and the protein subunit encoded by this gene was characterized as a truncated transit peptide(about 50% shorter than those of other plant AGPS1bs).In the present study,Ta AGPS1 b was fused with green fluorescent protein(GFP)in rice protoplast cells,and confocal fluorescence microscopy observations revealed that like other AGPS1 b containing the normal transit peptide,Ta AGPS1b-GFP was localized in chloroplasts.Ta AGPS1 b was further overexpressed in a Chinese bread wheat cultivar,and the transgenic wheat lines exhibited a significant increase in endosperm AGPase activities,starch contents,and grain weights.These suggested that Ta AGPS1 b subunit was targeted into plastids by its truncated transit peptide and it could play an important role in starch synthesis in bread wheat grains.