Involved in compound starch granule formation and starch synthesis in endosperm. May act as a regulatory scaffolding protein and affect starch synthesis and compound starch granule formation through direct interaction with isoamylase 1 (ISA1). Binds starch, amylopectin and amylose through its C-terminal carbohydrate-binding domain (CBM) in vitro. Interacts with SKIPA (PubMed:19339499). Interacts with ISA1 (PubMed:24456533). Localizes to granule-like structures in chloroplasts. Expressed in leaves, stems and panicles. Expressed at lower levels in roots and developing seeds. Contains a C-terminal (448-529) carbohydrate-binding domain (CBM). Slight reduction in plant height. Reduced size of the endosperm, reduced starch content of the endosperm and floury (opaque) endosperm.