Activation tagging in Arabidopsis

Activation tagging using T-DNA vectors that contain multimerized transcript ional enhancers from the cauliflower mosaic virus (CaMV) 35S gene has been applied to Arabidopsis plants. New activation-tagging vectors that confer r esistance to the antibiotic kanamycin or the herbicide glufosinate have bee n used to generate several tens of thousands of transformed plants. From th ese, over 30 dominant mutants with various phenotypes have been isolated. A nalysis of a subset of mutants has shown that overexpressed genes are almos t always found immediately adjacent to the inserted CaMV 35S enhancers, at distances ranging from 380 bp to 3.6 kb. In at least one case, the CaMV 35S enhancers led primarily to an enhancement of the endogenous expression pat tern rather than to constitutive ectopic expression, suggesting that the Ca MV 35S enhancers used here act differently than the complete CaMV 35S promo ter. This has important implications for the spectrum of genes that will be discovered by this method.