Biotechnological Manipulations in Sugarcane for Bioenergy Applications

Sugarcane is the most preferred feedstock for bioenergy productions owing to highly efficient C4 photosynthetic machinery, high sugar content, relatively high cellulosic biomass, and a favorable energy input and output ratio per hectare relative to other bioenergy-producing plants. In addition to table sugar production, sugarcane is being used as a feedstock for sugar derived and lignocellulose-derived bioethanol, and recently advanced biofuels like biodiesel are also obtained from metabolically engineered sugarcane also known as oilcane. Bioethanol is generally derived from sucrose by means of enzymatic hydrolysis. However, biotechnological manipulations help to enhance the accumulation of sugar in the sugarcane stalks and improve saccharification efficiency which in turn increases the bioethanol production. Sugar content and its concentration have been enhanced by altering the expression of sucrose synthase, trehalose phosphate, or soluble acid invertase genes. Altering lignin content or cell wall composition, particularly downregulation of caffeic acid O-methyltransferase (COMT) and 4-coumarate:coenzyme A ligase (Sh4-CL) or knock out of lignin biosynthesis genes by gene editing has also been demonstrated to improve lignocellulose to bioethanol conversions in sugarcane. Recently, metabolic engineering approach has been used to hyper accumulate neutral lipids such as triacyl glycerol (TAG) in the vegetative tissues of sugarcane by mostly co-expressing Wrinkled (WRI1), diacylglycerol acyltransferase1-2 (DGAT1-2), and oleosin1 (OLE1). Stored lipids or TAGs can be converted into biodiesel by transesterification process. Therefore, coproduction of bioethanol and biodiesel from sugarcane feedstock can be feasible through genetic manipulations using advanced biotechnological tools like genetic and metabolic engineering and genome editing.