Abstract: The present invention relates to isolated polypeptides having alpha-amylase activity and/or starch binding activity and/or plasmid targeting signals and to isolated polynucleotides encoding the polypeptides. The invention also relates to DNA constructs, vectors and host cells incorporating the polynucleotide sequences, methods for modulating starch content in plants, particularly plastids, as well as modifying plastid specific starch. The applicants have identified a class of alpha-amylases with plastid targeting signals and starch binding activity.