Tagging of a cryptic promoter that confers root-specific gus expression inArabidopsis thaliana

A 2.1-kb sequence was isolated by promoter trapping from an Arabidopsis tha liana transformant (T80) obtained by Agrobacterium-mediated T-DNA insertion . This sequence directed strong beta -glucuronidase (GUS) expression specif ically in roots. The promoter-gus fusion was used to transform other A. tha liana plants. Most of the transformants obtained exhibited stronger GUS act ivity 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 de tectable transcript and its physiological significance is unclear.