Tagging of a cryptic promoter that confers root-specific gus expression in Arabidopsis thaliana.

A 2.1-kb sequence was isolated by promoter trapping from an Arabidopsis thaliana transformant (T80) obtained by Agrobacterium-mediated T-DNA insertion. This sequence directed strong β-glucuronidase (GUS) expression specifically in roots. The promoter-gus fusion was used to transform other A. thaliana plants. Most of the transformants obtained exhibited stronger GUS activity in roots than the T80 line and a weak activity in leaves with a root/leaf ratio similar to that of T80. This 2.1-kb promoter sequence possesses a high number of motifs previously described as root-specific or aspecific enhancers. However, this promoter-like sequence is not associated with a detectable transcript and its physiological significance is unclear.