PLANT PHYSIOLOGY , Vol 111, Issue 4 1161-1167, Copyright © 1996 by American Society of Plant Biologists

GENE REGULATION AND MOLECULAR GENETICS

A Multiple-Stimuli-Responsive as-1-Related Element of parA Gene Confers Responsiveness to Cadmium but Not to Copper

M. Kusaba, Y. Takahashi and T. Nagata
Department of Biological Sciences, Graduate School of Science, University of Tokyo, Hongo, Bunkyo-ku, Tokyo, 113 Japan

The expression of parA, an auxin-regulated gene expressed during the culture of tobacco (Nicotiana tabacum L.) mesophyll protoplasts, is induced by cadmium. To identify the cadmium-responsive element, we examined the parA promoter using the GUS reporter gene. Cadmium responsiveness was retained in a 5[prime] deletion of the parA promoter to -78 bp, but it was nullified by further deletion to -49 bp, which implies that the region -49 to -78 bp contained a cadmium-responsive element. This region contains a sequence similar to as-1, an enhancer sequence from the cauliflower mosaic virus 35S RNA promoter that binds the nuclear factor ASF-1. We named the sequence in the parA promoter pas. Gel-shift assays revealed that pas and as-1 compete for the same DNA-binding nuclear protein(s). Since pentamers of either pas and as-1 were able to confer cadmium responsiveness on a minimal promoter but mutant as-1 was not, we propose that pas and as-1 are involved in cadmium-responsive gene expression. Neither pas nor as-1 conferred responsiveness to copper. The specificity of this response, involving the fuction of as-1- related elements including pas, is discussed.

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