ARABIDOPSIS GLABROUS1 GENE REQUIRES DOWNSTREAM SEQUENCES FOR FUNCTION

The Arabidopsis GLABROUS1 (GL1) gene is a myb gene homolog required fo r the initiation of trichome development. In situ hybridization reveal ed that the highest levels of GL1 transcripts were present in developi ng trichomes. In contrast, previous work had shown that putative promo ter sequences from the 5' noncoding region of the GL1 gene directed th e expression of a beta-glucuronidase (GUS) reporter gene only in stipu les. Deletion analysis of the 3' noncoding region of GL1 has identifie d an enhancer that is essential for GL1 function. Sequences from the r egion containing the enhancer, in conjunction with GL1 upstream sequen ces, direct the expression of a GUS reporter gene in leaf primordia an d developing trichomes in addition to stipules, indicating that the do wnstream enhancer is required for the normal expression pattern of GL1 .