Downstream elements from the pea albumin 1 gene confer sulfur responsiveness on a reporter gene

The levels of mRNAs for some of the sulfur-rich proteins in seeds are regulated by the level of sulfur supplied to the plants. In peas, there is a mechanism that lowers the level of mRNA for legumin and pea albumin 1 (PA1) when plants are grown under sulfur-deficient conditions. This mechanism acts after transcription initiation. In this study, a gene encoding PA1 was expressed in leaves of transgenic tobacco. Expression of the gene was controlled by the level of sulfur supplied to the plants, mimicking the behaviour of the intact gene in peas. A gene encoding a different high-sulfur protein, ovalbumin, was unresponsive to sulfur status and was used as a reporter gene to test defined regions of the PA1 gene for sulfur responsiveness. These constructs, together with a set of PA1 gene deletions, were tested in transgenic tobacco and yielded the following observations: the PA1 gene was sensitive to sulfur status in the leaf as well as the seed; intron processing of the PA1 transcript was not required for sensitivity to sulfur stress; both the coding region and the 3' flanking regions of the PA1 gene contained sequences which conferred sensitivity to sulfur stress; the sulfur-responsive sequence in the 3' region was contained within a 134-nucleotide segment downstream of the end of the coding sequence. We conclude that there are at least two downstream elements which confer sensitivity to sulfur supply.