Transgenic expression of trehalulose synthase results in high concentrations of the sucrose isomer trehalulose in mature stems of field‐grown sugarcane

Abstract

SummarySugarcane plants were developed that produce the sucrose isomers trehalulose and isomaltulose through expression of a vacuole-targeted trehalulose synthase modified from the gene in 'Pseudomonas mesoacidophila MX-45' and controlled by the maize ubiquitin (Ubi-1) promoter. Trehalulose concentration in juice increased with internode maturity, reaching about 600 mM, with near-complete conversion of sucrose in the most mature internodes. Plants remained vigorous, and trehalulose production in selected lines was retained over multiple vegetative generations under glasshouse and field conditions.

Isomaltulose Is Actively Metabolized in Plant Cells

“…The structural basis for this recognition is unknown (Kü hn and Grof, 2010;Geiger, 2011). Known Suc isomerases produce various ratios of isomaltulose and trehalulose from Suc in transgenic plants (Wu and Birch, 2007;Hamerli and Birch, 2011). The discovery of isomaltulose and trehalulose cleavage activities in plant cells, reported here, increases the complexity of mechanistic models needed to understand enhanced total sugar accumulation observed under some conditions in certain SI-expressing sugarcane lines Birch, 2007, 2010).…”

“…It is produced on an industrial scale from Suc by an enzymatic rearrangement using immobilized bacterial cells (Schiweck et al, 1991). With the characterization of Suc isomerase (SI) enzymes and the cloning of corresponding genes (Mattes et al, 1995;Bö rnke et al, 2001;Wu and Birch, 2005), direct production in plants became feasible, with potential cost savings over fermentative conversion of Suc harvested from plants (Börnke et al, 2002b;Kunz et al, 2002;Wu and Birch, 2007;Basnayake et al, 2011;Hamerli and Birch, 2011).…”

“…Substantial isomer accumulation (approximately 440 mmol g 21 fresh weight) has been achieved in sugarcane (Saccharum interspecific hybrids) expressing transgenes for SI enzymes targeted to the Suc storage vacuoles (Wu and Birch, 2007). However, isomer levels in field-grown sugarcane have not exceeded the usual Suc concentrations (more than 500 mmol g 21 fresh weight) in elite sugarcane cultivars (Basnayake et al, 2011;Hamerli and Birch, 2011). Much lower isomaltulose concentrations (approximately 15 mmol g 21 fresh weight) have been achieved in potato (Solanum tuberosum) tubers expressing an apoplast-targeted SI (Bö rnke et al, 2002b).…”

Molecular Breeding of Grasses by Transgenic Approaches for Biofuel Production

“…The transgenic sugarcane plants accumulated the trehalulose up to 600 mM in juice from mature nodes. Contrary to the case of the sorbitol-accumulating sugarcane, the trehalulose-accumulating transgenic plants were vigorous, and trehalulose production in selected lines was retained over multiple vegetative generations under glasshouse and field conditions (Hamerli & Birch, 2011).…”

“…The average amounts of sorbitol detected in the most productive line were 120 mg g -1 dry weight (equivalent to 61% of the soluble sugars) in the leaf lamina and 10 mg g -1 dry weight in the stalk pith, but the accumulation caused evident necrosis in expanding leaves and reduced growth (Chong et al, 2007). More recently, another group focused on production of the sucrose isomer trehalulose (Hamerli & Birch, 2011). The transgenic sugarcane plants accumulated the trehalulose up to 600 mM in juice from mature nodes.…”