A distal promoter region of the rice seed storage protein glutelin gene enhanced quantitative gene expression

Abstract

We have demonstrated previously that a distal promoter region of the rice seed storage protein glutelin (Gt1) gene plays a role in increasing the quantitative level of gene expression. To determine the approximate location of cis-acting elements, if any, for the increased promoter activity, 18 progressive 5′- or internal deletions were introduced into the distal promoter region between −5.1 k and −507 relative to the transcription initiation site. The deleted promoters were fused to the coding sequence of β-glucuronidase (GUS) gene, and the fusion genes were introduced via protoplasts into homologous rice plants. GUS activities were assayed in developing seeds and vegetative organs of mature plants containing wild-type and mutant constructs. The results showed that the 4.6 kb-long wild-type distal promoter enhanced the quantitative level of GUS reporter gene by nearly 100-fold and also increased the frequency of plants showing high levels of expression. Any deletions from the 4.6 kb distal promoter region reduced the GUS activity but no distinct element was evident within the region by this analysis. We suggest that the distal promoter region may form a favorable chromatin structure to maximize the quantitative level of the glutelin gene expression. This finding also has an important practical implication in using the glutelin gene promoter to achieve a high expression level of introduced gene products in transgenic plants.