Strategies for expressing multiple foreign genes in plants as polycistronic constructs

With an ever-increasing frequency, it has become desirable to express many foreign genes in the same transgenic plant. A range of approaches to this problem have been explored in the period since gene transfer was developed as a useful tool in plant science. These have ranged from assembly of multiple transcription units on a single DNA vector, to the execution of several independent transformations involving single genes followed by successive rounds of hybridization to yield plant lines with the desired combination of genes, to cotransformation with multiple plasmids followed by molecular screening to identify desired transgenic plants. Recent developments have provided new alternatives to the problem of the expression of multiple foreign genes in plants, approaches that revolve around the expression of polycistronic mRNAs. This review summarizes the current status of the area of polycistronic gene expression in transgenic plants, within the context of multigene expression.