Abstract: The invention relates to a method for changing the glucan chain lengths using fusion protein domains of various starch synthase enzymes in any starch or starch granule producing organism. The invention relates to identification of a GLucan ASSociation domain (herein after referred to as “GLASS” domain) of granule bound starch synthase (GBSS) used in combination with any other GLYcosyl TRransferase domain otherwise referred to as pfam00534-catalytic domain (herein after referred to as “GLYTR” domain) of one or more of any of the other starch synthase enzymes. The invention relates to identifying and using the new and surprising discovery that starch synthases are composed of at least two distinct functional domains herein after labeled as “GLASS” and “GLYTR”. More specifically, this invention relates to the genetic constructs that encode the fusions of the above domains and to the plants transformed with said constructs.