Identification of seed dormancy mutants by activation tagging

Activation tagging is an important tool for gene discovery in plants. This method utilizes a T-DNA sequence that contains four tandem copies of the cauliflower mosaic virus 35S enhancer sequence or promoters oriented outward to the T-DNA border sequences. These elements enhance the expression of genes neighboring on either side of the randomly integrated T-DNA, resulting in gain-of-function phenotypes. Activation tagging has identified a number of genes, including those fundamental to plant development, such as the floral inducer gene, FLOWERING LOCUS T  (FT  ). The methods surrounding activation-tagging approaches are described in this chapter. While seeds have generally not been the targets of these methods in the past, activation tagging provides a powerful approach to uncover genes involved in seed dormancy and germination, including those that mediate hormone signal transduction.