Transgenic sugar beets as industrial plants

Development of new industrial plants is one of the main purposes of modern biotechnology. Whereas transgenic oilseed crops have entered the state of agroindustrial exploitation, modification of plant carbohydrate metabolism is still in its infancy. Despite of its role as one of the worlds most important crops and a high potential of sugar and sugar derivatives as food ingredients and precursors of economically valuable substances sugarbeet has become amenable to metabolic engineering only slowly. The most serious problems have been imposed by inefficient and poorly reproducible regeneration protocols and an almost complete lack of cloned genes known to be expressed specifically in the storage root. The current state of transformation technology suggests that many metabolic alterations of sugar beet root metabolism can be introduced into the plant, if a cloned gene is available pro-viding the enzyme function needed to catalyze the required modification step. Examples of this category are elimination of unde-sired byproducts like raffinose, invert sugar and dextran, one step synthesis of simple sugar derivatives, e.g. ketosugars or fructans, and also production of ethanol and possibly other products of microbial fermentations by post harvest induction of the necessary enzymes. Among the more distant breeding objectives are the synthesis of better pectins and lignin free cellulose in sufficient amounts and quality to allow technical applications. This will be feasible only when most or all the genes involved in synthesis of these biopolymers will be known. Transformation and regeneration of sugarbeet has now been improved significa-ntly. Moreover, effective molecular methods are available for isolation of developmentally regulated genes. Molecular breeding of a first generation of metabolically engineered sugarbeet cultivars should thus take no longer and not be more difficult than in the case of other transgenic crops like oilseed rape, that are now used commercially.