Metabolic Engineering Converts Sugarcane into an Oil Producing Crop

Metabolic engineering to divert carbon flux from sucrose to oil in a high biomass crop like sugarcane has been proposed as a strategy to boost lipid yields per acre for biodiesel production. The energy content of plant oils in the form of triacylglycerols (TAGs) is two-fold greater compared to carbohydrates. However, vegetative plant tissues do not accumulate oil to a significant amount since fatty acid synthesis in these tissues serves primarily membrane construction, in addition TAGs undergo rapid turnover. Therefore, our objectives include metabolic engineering to:

1.) increase fatty acid synthesis,

2.) increase TAG synthesis from diacyl-glycerol and acyl-CoA

3.) optimize TAG storage

4.) minimize TAG hydrolysis in vegetative tissues.

Constitutive single or multiple gene expression/suppression cassettes were generated and co-delivered with the selectable nptII expression cassette by biolistic gene transfer into sugarcane callus. Plants were regenerated on geneticin containing culture medium and analyzed for presence and expression of target constructs by PCR and RT-PCR, respectively. Quantitative real PCR was performed to study the level of gene expression in transgenic TAG plants in different vegetative tissues. Plants were analyzed for TAG content by gas-chromatography and mass spectrometry (GC-MS).

TAG accumulation increased several hundred fold in vegetative tissues of transgenic sugarcane with co-expression/co-supression of multiple target genes. While events with low TAG accumulation co-expressed either fewer transgenes, or expressed the transgenes at lower levels. This research outcome will add value to the abundant sugarcane post-harvest residues for production of advanced biofuels.