Production of microbial mutan polysaccharide by expression of a mutansucrase gene (gtfI) in sugarcane

Due to its high productivity and sucrose content, sugarcane (Saccharum officinarum) is becoming the source of high-value bioproducts. Expression of bacterial extracellular polysaccharide genes in non-biopolymer accumulating plants is an excellent resource for production of added-value products. To this end, an expression cassette containing a full-length glucosyltransferase (gtfI) gene from Streptococcus downei driven by a CaMV promoter was expressed in a commercial sugarcane cultivar (CP48-103) using a biolistic approach. Copy number was assessed for a number of selected transgenic sugarcane lines by DNA blot analysis, where it was corroborated that each transgenic line contained at least two gtfI copies. The southern blot analysis of gtfI-expressing lines showed that the number of integrated copies ranged from two to four. The expression of gtfI in transgenic sugarcane plants was confirmed by mRNA blot analysis and qRT-PCR analysis. The expression of gtfI in transgenic sugarcane plants resulted in an approximate 30% reduction in sucrose accumulation, suggesting that mutansucrase actively converted sucrose to mutan polymer. In internodal stalk tissues, mutan polymer accumulated up to 55.9 mg/g FW, which apparent through glucan staining. The levels of glucose and fructose increased nearly by twofold, suggesting that mutansucrase may also have hydrolyzing activity.