Analysis of the promoter of the auxin-inducible gene, parC, of tobacco.

The auxin-responsive region (AuxRR) in the promoter of the parC gene was analyzed in transgenic tobacco plants in which the 5' flanking region of the parC promoter was placed upstream of the gene for beta-glucuronidase (GUS). The AuxRR was located between nucleotides (nt) -226 and -54. Detailed dissection of this segment revealed that the presence of the non-contiguous sequences from nt -226 to -151 and from nt -84 to -54 was required for the expression of the auxin responsiveness of the parC promoter. The sequence from nt -226 to -151 was found to contain a sequence which resembles the as-1 element in the 35S promoter of cauliflower mosaic virus (CaMV). Although it has been reported that the as-1 element is involved in auxin responsiveness [Liu and Lam (1994) J. Biol. Chem. 269: 668], we showed that introduction of a point mutation into the as-1-like sequence completely eliminated auxin responsiveness, a result that suggests that the sequence is indispensable for auxin responsiveness. However, the presence of the as-1-like sequence alone was not sufficient for auxin responsiveness, since the segment (nt -226 to -84) that included the as-1-like sequence failed to confer auxin responsiveness on the core promoter. It is possible that the two separately located sequences play specific roles in interactions with trans-factors that are required for the expression of the auxin responsiveness of the parC promoter.