Increase of amylose content of sweetpotato starch by RNA interference of the starch branching enzyme II gene (IbSBEII)

Abstract

In the storage roots of sweetpotato (Ipomoea batatas (L.) Lam. cv. Kokei 14), 10 to 20% of the starch is essentially unbranched linear amylose and the other major component is branched amylopectin. The starch branching enzymes, which are responsible for production of amylopectin to form a-1,6-linkages in the glucan can be divided into two classes, class A (e.g. potato and maize SBEII, pea SBEI) and class B (e.g. potato and maize SBEI, pea SBEII). On the bases of the registered cDNA of sweetpotato SBEII (IbSBEII) encoding class A branching enzyme, we constructed doublestranded RNA (dsRNA) interference vectors and introduced them into sweetpotato genome via Agrobacterium-mediated gene transformation. We obtained eight independent transgenic plants by using two kinds of RNA interference (RNAi) constructs, encoding GBSSI 1st intron-spliced RNA or a GUS fragment-spliced RNA, respectively. All transgenic plants were confirmed not to express IbSBEII by RT-PCR and to have the starch with a higher amylose content than the nontransgenic control (up to 25% compared to 10% in the control). Both constructs induced the same level of silencing of IbSBEII in all transgenic plants. The morphological characters showed no significant differences between the transgenic and control plants. Starch yield of transgenic tubers was slightly lower than that of non-transgenic tubers. The starch granules of the transgenic plants were similar to those of typical sweetpotato starchs in shape and the distribution in granule size, but slightly different in grain structure.

Efficient Agrobacterium tumefaciens-mediated transformation using embryogenic suspension cultures in sweetpotato, Ipomoea batatas (L.) Lam.

“…Different explants such as leaves, petioles, stems, storage roots, and embryogenic calli have been used for A. tumefaciens-mediated transformation of sweetpotato and stable transgenic sweetpotato plants have also been reported, but in most cases only a low transformation efficiency was obtained (Newell et al 1995;Gama et al 1996;Morán et al 1998;Otani et al 1998Otani et al , 2001Otani et al , 2003Cipriani et al 1999Cipriani et al , 2001Wakita et al 2001;Kimura et al 2001;Song et al 2004;Shimada et al 2006;Luo et al 2006). In comparison, apical meristem-derived embryogenic calli can give an improved transformation efficiency in sweetpotato (Gama et al 1996;Otani et al 1998), but they are not readily available target tissues for most of sweetpotato cultivars due to low frequencies of embryogenic callus formation in apical meristem cultures (Al-Mazrooei et al 1997;Liu et al 1997;Wang et al 1998).…”

Genotype Independent Regeneration and Agrobacterium?mediated Genetic Transformation of Sweet Potato (Ipomoea batatas L.)

“…A. tumefaciens mediated transformation in sweet potato was well established by several workers (Al-Juboory and Skirvin 1991, Carelli et al 1991, Prakash and Varadarajan 1991, Lowe et al 1994, Otani et al 2001. In general, these procedures have been mostly genotype-dependent with lower transformation efficiency (Otani et al 2003, Song et al 2004, Shimada et al 2006, Luo et al 2006, and often difficult to reproduce (Lowe et al 1994). Agrobacterium-mediated transformation in sweet potato has also been applied for regeneration via somatic embryogenesis using somatic embryos or organs as explants by several workers (Pido et al 1995, Newell et al 1995, Gama et al 1996, Otani et al 1998, Luo et al 2006).…”

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

“…Nakatani and Komeichi (1992) reported a positive correlation between ADP-glucose pyrophosphorylase (AGPase) activity and starch content in storage roots. In addition, transgenic plants with suppressed expression of the genes encoding starch branching enzyme II (SBEII) or granule bound starch synthase I (GBSSI) have been shown to have reduced starch content (Noda et al 2002;Shimada et al 2006). These studies, however, did not provide any experimental evidence that the dry matter content of storage roots might be improved by genetic engineering.…”