Regulation of expression of an auxin-induced soybean sequence by cadmium

An auxin-regulated soybean sequence has been characterized and shown to be induced by the heavy metals cadmium, silver, and copper. Cadmium induces the accumulation of two size classes of mRNA: a 1-kilobase (kb) RNA class, which is the same size as the RNA class induced by auxin, silver, and copper, and a 1.4-kb RNA class. DNA sequence analysis of cDNA clones and a soybean genomic fragment has shown the presence of an intron in this gene. A restriction fragment probe isolated from the intron segment hybridizes specifically to the 1.4-kb mRNA. The transcription rate of this sequence is rapidly increased following exposure of soybean primary leaves to cadmium, as assayed by nuclear run-off transcription experiments. These results suggest that cadmium not only induces the transcription of a specific soybean sequence, but interferes with the processing of the precursor mRNA, resulting in the accumulation of the 1.4-kb mRNA precursor species.