Targeting transgene expression in research, agricultural, and environmental applications: Promoters used in plant transformation

Plant genetic engineering has contributed substantially to the understanding of gene regulation and plant development, in the generation of transgenic organisms for widespread usage in agriculture, and has increased the potential uses of crops for industrial and pharmaceutical purposes. As the application of genetically engineered plants has widened, so has the need to develop methods to fine-tune control of transgene expression. The availability of a broad spectrum of promoters that differ in their ability to regulate the temporal and spatial expression patterns of the transgene can dramatically increase the successful application of transgenic technology. Indeed, a variety of promoters is necessary at all levels of genetic engineering in plants, from basic research discoveries, concepts and questions, to development of economically viable crops and plant commodities, to addressing legitimate concerns raised about the safety and containment of transgenic plants in the environment. This review covers the characterization and usage of a broad range of promoters employed in plant genetic engineering, including the widespread use of plant promoters with viral and plant origin that drive constitutive expression. Also covered are selected tissue-specific promoters from fruit, seed and grain, tubers, flowers, pistils, anther and pollen, roots and root nodules, and leaves and green tissue. Topics also include organellar promoters, and those found in specific cell types, as well as the development and evaluation of inducible (endogenous and exogenous origin) and synthetic plant promoter systems. Discussions on the relevance and potential pitfalls within specific applications are included.