A DNA sequence element that confers seed-specific enhancement to a constitutive promoter

Abstract

Genes encoding beta-conglycinin, a soybean seed storage protein, are expressed only in seeds during mid-to-late stages in embryogeny. It was previously determined that a DNA sequence 200 nucleotides upstream of the transcriptional start site of the gene encoding the alpha'-subunit of beta-conglycinin is essential for regulated gene expression in transgenic plants. The regulatory effect of this DNA element was tested by inserting the element in different positions and different orientations within a chimeric constitutively expressed reporter gene. The reporter gene was comprised of the 35S promoter from cauliflower mosaic virus (CaMV), a gene encoding chloramphenicol acetyltransferase (CAT) and the polyadenylation signal from the alpha'-subunit gene. The element had no significant effect on the expression of the CAT gene in roots, stems, or leaves, regardless of the position of its insertion (i.e. 5 or 3 of the gene). However, there was 25- to 40-fold enhancement of CAT gene expression in seeds during mid-to-late stages of embryo development when the element was placed in either orientation within the 35S promoter. There was 2- to 4-fold enhancement of CAT activity when the element was placed 3' of the CAT coding sequence. No enhancement was detected when the element was placed downstream of the 3' non-coding region. This is, to our knowledge, the first identification of a cis-acting element that enhances gene expression in a tissue-specific and temporally regulated manner during embryo development in plants.