Strategies for metabolic pathway engineering with multiple transgenes

The engineering of metabolic pathways in plants often requires the concerted expression of more than one gene. While with traditional transgenic approaches, the expression of multiple transgenes has been challenging, recent progress has greatly expanded our repertoire of powerful techniques making this possible. New technological options include large-scale co-transformation of the nuclear genome, also referred to as combinatorial transformation, and transformation of the chloroplast genome with synthetic operon constructs. This review describes the state of the art in multigene genetic engineering of plants. It focuses on the methods currently available for the introduction of multiple transgenes into plants and the molecular mechanisms underlying successful transgene expression. Selected examples of metabolic pathway engineering are used to illustrate the attractions and limitations of each method and to highlight key factors that influence the experimenter's choice of the best strategy for multigene engineering.