Molecular characterization of genes encoding isoamylase-type debranching enzyme in tuberous root of sweet potato, <i>Ipomoea batatas</i> (L.) Lam.

Abstract

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 (IbISA1, IbISA2, IbISA3) encoding isoamylase from sweet potato (Ipomoea batatas (L.) cv. White Star). Deduced amino acid sequences of the three isolated IbISAs have the specific regions that are highly conserved among the α-amylase family members. The product of IbISA2 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 IbISA2 was higher than that of the other two IbISAs (IbISA1 and IbISA3) 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 ISA gene expression may depend on the differences in sink organ type between tuberous roots and seeds. The molecular characterization of three IbISA genes and their expression analysis in this study will contribute to further studies on starch biosynthesis in sweet potato, especially in storage root.

Engineering Properties of Sweet Potato Starch for Industrial Applications by Biotechnological Techniques including Genome Editing

“…DBEs (α-1,6-glucanohydrolases) cleave branch points and determine the structure of amylopectin [45]. The two classes of DBE, isoamylase (ISA) and pullulanase (PUL), directly hydrolyze the β-1,6-glucosic linkages of polyglucans.…”

“…Few studies have been conducted on DBEs in sweet potato. At least two copies of IbIsa1 are present in the sweet potato genome [45]. IbIsa1 strongly expresses in the tuberous root.…”

Integrated mRNA and Small RNA Sequencing Reveals a microRNA Regulatory Network Associated with Starch Biosynthesis in Lotus (Nelumbo nucifera Gaertn.) Rhizomes

“…Thus far, many genes associated with rhizome development have been researched in lotus. Among them, SUS [ 10 ], UDP [ 11 ], PGM [ 12 , 13 ], AGP [ 14 ] are closely related to the synthesis of total starch, GBSS [ 15 , 16 ] is a key gene affecting amylose synthesis; SS [ 17 , 18 ], SBE [ 17 ] and DBE [ 19 , 20 ] are involved in the synthesis of amylopectin.…”