Molecular characterization of genes encoding isoamylase-type debranching enzyme in tuberous root of sweet potato, (L.) Lam.

Isoamylase (ISA) is a starch debranching enzyme that removes α-1,6-glucosidic linkages in α-polyglucans such as amylopectin. From previous studies, plant isoamylases have been shown to play a crucial role in amylopectin biosynthesis; however, little is known about their function in storage root tissues of plants such as cassava, yam and sweet potato. In this study, we isolated cDNA clones and characterized the cDNA nucleotide sequences of three genes (, , ) encoding isoamylase from sweet potato ( (L.) cv. White Star). Deduced amino acid sequences of the three isolated s have the specific regions that are highly conserved among the α-amylase family members. The product of is predicted to be enzymatically inactive, like other plant ISA2s, due to replacement of amino acid residues that are important for hydrolytic reaction. qRT-PCR analysis demonstrated that expression of was higher than that of the other two s ( and ) in tuberous root at 109 days after planting, at which stage of tuberous root was at which stage tuberous roots were almost fully developed almost developed. This expression pattern observed in our experiments was different from that in other sink organs, such as seeds (endosperms), indicating that orchestration of gene expression may depend on the differences in sink organ type between tuberous roots and seeds. The molecular characterization of three genes and their expression analysis in this study will contribute to further studies on starch biosynthesis in sweet potato, especially in storage root.