Kinetic Modelling of Sucrose Metabolism: a Powerful Predictive Tool for Genetic Manipulation of Sugar Content in Sugarcane

The apparent failure to make significant progress in increasing the sucrose content of commercial varieties during the past two decades has led to the speculation that a yield plateau has been reached. Several research groups have therefore been investigating genetic manipulation of sucrose metabolism as an alternative approach, to supplement conventional breeding. However, the general lack of knowledge regarding the complexity of sucrose metabolism and control of sugar accumulation makes the selection of candidate genes for manipulation extremely difficult. Over the past few years the Institute for Plant Biotechnology has accumulated a significant amount of information about carbon partitioning, enzyme and metabolite levels, and metabolic fluxes in the sugarcane culm. This information was used to develop a kinetic metabolic model of sucrose synthesis and breakdown in the culm. The model accurately simulates the characteristic sucrose accumulation pattern observed in sugarcane. Surprisingly, the model predicted limited control on sucrose metabolism for some of the current genes being targeted for manipulation. By referring to the example of genetically modified sugarcane with reduced acid invertase, it will be illustrated that this model could become an invaluable tool in developing a strategy to manipulate metabolism in sugarcane.