The Structure of Plant Gene Promoters

Plant promoters for genes transcribed by RNA polymerase II have been studied for more than a decade. Although far behind mechanistic studies dealing with yeast and animal promoter structure and function, much has been learned about cis-regulatory elements for environmental, developmental and stimulus-induced plant promoters and about plant transcription factors that specifically bind to cis-acting elements. Plant promoter cis-acting elements are routinely defined by testing promoters and promoter fragments fused to reporter genes in transient assays (i.e., transfection of plant protoplasts or particle bombardment of plant cells or tissues) or in stably transformed plants. In many cases, promoters, promoter fragments, or multimerized minimal cis-elements are tested in heterologous plants that provide good sources for protoplasts or are easily transformable. While there has been some criticism waged at the reliability of employing heterologous systems in promoter analyses, it can be argued that functionally important cis-acting elements should display a high degree of conservation among plants that respond to identical inducers or to developmental programs.