Carbohydrate components in sweetpotato storage roots: their diversities and genetic improvement.

Carbohydrates are important components in sweetpotatoes in terms of both their industrial use and eating quality. Although there has been a narrow range of diversity in the properties of sweetpotato starch, unique varieties and experimental lines with different starch traits have been produced recently both by conventional breeding and genetic engineering. The diversity in maltose content, free sugar composition and textural properties in sweetpotato cultivars is also important for their eating quality and processing of storage roots.

A high-density SNP genetic map consisting of a complete set of homologous groups in autohexaploid sweetpotato (Ipomoea batatas).

Sweetpotato (Ipomoea batatas) is an autohexaploid species with 90 chromosomes (2n = 6x = 90) and a basic chromosome number of 15, and is therefore regarded as one of the most challenging species for high-density genetic map construction. Here, we used single nucleotide polymorphisms (SNPs) identified by double-digest restriction site-associated DNA sequencing based on next-generation sequencing technology to construct a map for sweetpotato. We then aligned the sequence reads onto the reference genome sequence of I.

Survey of genome sequences in a wild sweet potato, Ipomoea trifida (H. B. K.) G. Don.

Ipomoea trifida (H. B. K.

Inhibition of the expression of the starch synthase II gene leads to lower pasting temperature in sweetpotato starch.

The sweetpotato cultivar Quick Sweet (QS) with a lower pasting temperature of starch is a unique breeding material, but the biochemical background of this property has been unknown. To assess the physiological impact of the reduced isoform II activity of starch synthase (SSII) on the starch properties in sweetpotato storage root, transgenic sweetpotato plants with reduced expressions of the SSII gene were generated and evaluated. All of the starches from transgenic plants showed lower pasting temperatures and breakdown measured by a Rapid Visco Analyzer.

Altered carbohydrate metabolism in the storage roots of sweet potato plants overexpressing the SRF1 gene, which encodes a Dof zinc finger transcription factor.

In order to characterize the functions of the sweetpotato SRF1 gene, which encodes a Dof zinc finger transcriptional factor preferentially expressed in the storage roots, we isolated its full length cDNA and produced transgenic sweetpotato plants with altered SRF1 expression levels. The isolated cDNA of SRF1 encoded a polypeptide of 497 amino acids and was closely related to the cyclic Dof factors of Arabidopsis and the ascorbate oxidase binding protein of pumpkin. SRF1 was most highly expressed in storage roots, although some expression was also observed in other vegetative tissue.

Expression of class I knotted1-like homeobox genes in the storage roots of sweetpotato (Ipomoea batatas).

As a first step in clarifying the involvement of class I knotted1-like homeobox (KNOXI) genes in the storage root development of sweetpotato (Ipomoea batatas), we isolated three KNOXI genes, named Ibkn1, Ibkn2 and Ibkn3, expressed in the storage roots. Phylogenetic analysis showed that Ibkn1 was homologous to the SHOOT MERISTEMLESS (STM) gene of Arabidopsis, while Ibkn2 and Ibkn3 were homologous to the BREVIPEDICELLUS (BP) gene. Of these, expression of Ibkn1 and Ibkn2 were upregulated in developing and mature storage roots compared with fibrous roots.

Inhibition of the gene expression for granule-bound starch synthase I by RNA interference in sweet potato plants.

Granule-bound starch synthase I (GBSSI) is one of the key enzymes catalyzing the formation of amylose, a linear alpha(1,4)D-glucan polymer, from ADP-glucose. Amylose-free transgenic sweet potato plants were produced by inhibiting sweet potato GBSSI gene expression through RNA interference. The gene construct consisting of an inverted repeat of the first exon separated by intron 1 of GBSSI driven by the CaMV 35S promoter was integrated into the sweet potato genome by Agrobacterium tumefaciens-mediated transformation.

Analysis of genes developmentally regulated during storage root formation of sweet potato.

To identify the genes involved in storage root formation of sweet potato (Ipomoea batatas), we performed a simplified differential display analysis on adventitious roots at different developmental stages of the storage root. The expression patterns were confirmed by semiquantitative RT-PCR analyses. As a result, 10 genes were identified as being developmentally regulated and were named SRF1-SRF10.

Structural characterization of the dihydroflavonol 4-reductase B (DFR-B) gene in the sweet potato.

A genomic fragment containing the dihydroflavonol 4-reductase B (DFR-B) gene was cloned from the sweet potato (Ipomoea batatas) and its nucleotide sequence was analyzed. The exons and flanking regions were highly homologous to those of previously reported DFR-B genes of the Japanese morning glory, whereas the introns and the intergenic region were less conserved. In addition to the sequences of three miniature inverted-repeat transposable elements (MITEs) and one direct repeat previously reported in the DFR-B gene of Japanese morning glory, two mobile element-like sequences were newly identified in the sweet potato DFR-B gene.

Decreased sucrose content triggers starch breakdown and respiration in stored potato tubers (Solanum tuberosum).

To change the hexose-to-sucrose ratio within phloem cells, yeast-derived cytosolic invertase was expressed in transgenic potato (Solanum tuberosum cv. Desirée) plants under control of the rolC promoter. Vascular tissue specific expression of the transgene was verified by histochemical detection of invertase activity in tuber cross-sections.