Location of the cis-acting auxin-responsive region in the promoter of the par gene from tobacco mesophyll protoplasts.

We have isolated a genomic clone of an auxin-regulated par gene, which is expressed during the transition from G0 phase to S phase in the early stage of tobacco mesophyll protoplasts cultured in vitro, from a tobacco genomic library using the par cDNA as a probe. When a chimeric gene, in which a reporter gene for bacterial beta-glucuronidase (GUS) was placed downstream of the 5' flanking sequences of the par gene, was introduced into tobacco mesophyll protoplasts by electroporation, the chimeric gene elicited auxin-regulated expression of GUS activity. Because deletion of a 111-base-pair (bp) direct repeat in the 5' flanking sequences of the par gene abolished the auxin-induced GUS activity, it is deduced that in the 111-bp direct repeat of the par gene promoter is localized an auxin-responsive region, which regulates auxin-mediated activation of transcription.