Reuteran and levan as carbohydrate sinks in transgenic sugarcane

• Published in: Planta 2012-12, Vol.236 (6), p.1803-1815
• Main Authors: Bauer, Rolene, Basson, Carin E., Bekker, Jan, Eduardo, Iban, Rohwer, Johann M., Uys, Lafras, van Wyk, Johannes H., Kossmann, Jens
• Format: Article
• Language: English
• Subjects: Agriculture; Bacterial Proteins - genetics; Biological and medical sciences; Biomass; Biomedical and Life Sciences; Biopolymers; Brassica; Callus; Carbon - metabolism; Carbon Radioisotopes - analysis; Cell lines; Cell walls; Ecology; Forestry; Fructans; Fructans - metabolism; Fundamental and applied biological sciences. Psychology; Glucans - metabolism; Glycosyltransferases - genetics; Lactobacillus - enzymology; Lactobacillus - genetics; Life Sciences; Open reading frames; Original Article; Plant Sciences; Plants; Plants, Genetically Modified; Polysaccharides; Polysaccharides - metabolism; Saccharum - cytology; Saccharum - genetics; Saccharum - growth & development; Saccharum - metabolism; Starch; Starch - analysis; Starch - metabolism; Starches; Sucrose - analysis; Sucrose - metabolism; Sugar cane; Sugarcane; Tissue Culture Techniques; Transgenes; Transgenic plants
• ISSN: 0032-0935; 1432-2048
• DOI: 10.1007/s00425-012-1731-x

The present study reports the effect of high molecular weight bacterial fructan (levan) and glucan (reuteran) on growth and carbohydrate partitioning in transgenic sugarcane plants. These biopolymers are products of bacterial glycosyltransferases, enzymes that catalyze the polymerization of glucose or fructose residues from sucrose. Constructs, targeted to different subcellular compartments (cell wall and cytosol) and driven by the Cauliflower mosaic virus-35S: maize-ubiquitin promoter, were introduced into sugarcane by biolistic transformation. Polysaccharide accumulation severely affected growth of callus suspension cultures. Regeneration of embryonic callus tissue into plants proved problematic for cell walltargeted lines. When targeted to the cytosol, only plants with relative low levels of biopolymer accumulation survived. In internodal stalk tissue that accumulate reuteran (max 0.03 mg/g FW), sucrose content (ca 60 mg/g FW) was not affected, while starch content (< 0.4 mg/g FW) was increased up to four times. Total carbohydrate content was not significantly altered. On the other hand, starch and sucrose levels were significantly reduced in plants accumulating levan (max 0.01 mg/g FW). Heterologous expression resulted in a reduction in total carbohydrate assimilation rather than a simple diversion by competition for substrate.