Approaches to minimize variation of transgene expression in plants

Genetic transformation of plants has become a widely used technology that serves multiple purposes in plant biology research. However, considerable variation of transgene expression is often observed within populations of transgenic plants transformed with the same transgene construct. This inter-transformant variation of transgene expression hampers proper evaluation of transgenes and might be most undesirable when high-throughput transgene screening is intended. The general plant transformation strategy today is to generate a sufficiently high number of transgenic plants to find some transformants with the desired level of expression. To reduce cost, labor and interpretational flaws, multiple efforts are being directed toward achieving stable expression of transgenes with an expected level of expression. Various factors are thought to contribute to transgene expression variation including the transgene copy number, RNA silencing, transgene insertion site and the employment of certain regulatory sequences to drive transgene expression. This review provides an update on current methodologies to minimize inter-individual variation of transgene expression in nuclear transformed plants.