High level accumulation of α-glucan in maize kernels by expressing the gtfD gene from Streptococcus mutans

Abstract

Glucosyltransferases (GTFs, EC.2.4.1.5) are bacterial enzymes that catalyze the polymerization of glucose residues from sucrose, leading to the production of high molecular weight glucan with a-1,3 /a-1,6 linkages. Such glucans, with many potential food and industrial applications, do not normally exist in higher plants. We fused a mutant form of the gtfD gene from Sreptococcus mutans with the maize (Zea mays L.) chloroplastic Brittle 1 transit peptide for amyloplast targeting. This construct, driven by the ubiquitin promoter, was introduced into maize by Agrobacterium-mediated transformation. We developed a novel HPLC-based method that enabled us differentially to distinguish transgene glucan from other endogenous polysaccharides in maize kernels. Using this method, we screened over 100 transgenic plants for the presence of GTF-produced glucan whose content varied between 0.8 and 14% of dry weight in the mature transgenic seeds. The mature transgenic plants were indistinguishable from wildtype plants in growth rate and morphology. Furthermore, starch granule size in the transgenic maize kernel was unaffected by the accumulation of the foreign polysaccharide. Mutation in Sh2, which encodes a subunit of ADP-glucose pyrophosphorylase, had no effect on glucan accumulation caused by gtfD expression. Our results indicated that high levels of novel carbohydrate polymer can be accumulated in crop plants through transgene technology.

Transcriptome sequencing and differential expression analysis of seed starch accumulation in Chinese chestnut Metaxenia

“…Glycosyltransferases (GTFs) are enzymes (EC 2.4) that establish natural glycosidic linkages. They catalyze the transfer of saccharide moieties from an activated nucleotide sugar (also known as the “glycosyl donor”) to a nucleophilic glycosyl acceptor molecule, the nucleophile of which can be oxygen carbon, nitrogen, or sulfur based [ 28 , 29 ]. In our study, the expression levels of genes encoding the glycosyl hydrolase family and phosphoglucomutase/phosphomannomutase were shown to play an important role in the seeds from all three pollination combinations.…”

Prospects for increasing starch and sucrose yields for bioethanol production

“…Farré et al, 2001;Gerrits et al, 2001); traditionally, this metabolite was thought to be confined to the cytosol. Reports of successful generation of novel glucans include potato plants that synthesize starch-fructan hybrid polymers (Gerrits et al, 2001), small amounts of cyclodextrins (Oakes et al, 1991) and starch granules apparently coated with a-1,3, a-1,6 glucan (Nazarian Firouzabadi et al, 2007), and maize plants in which up to 8% of the kernel dry mass is fructan (Caimi et al, 1996) or up Starch and sugar for bioethanol production 553 to 14% of the kernel dry mass is an a-1,6 glucan (Zhang et al, 2007). However, I am not aware of any evidence so far showing that total polymeric non-structural carbohydrate contents (starch plus novel glucan or fructan) are significantly increased in any of these plants.…”

Genetic Enhancement of Grain Quality-Related Traits in Maize

“…This could potentially be exploited within the high-fructose maize syrup market. Moreover, Zhang et al (2007) have developed transgenic maize endosperm, via the introduction of a Streptococcus mutans gtfD gene, that accumulates novel glucan (oligo-and polysaccharides composed solely of glucose molecules) polymers at levels relevant to commercial production. The expression of that gene yielded fully functional GTF-D enzyme as shown by accumulation of novel soluble -(1→6)-linked glucan at high levels in the mature maize kernels (up to 14% of their dry weight).…”