Deletion analysis of the Brassica napus cruciferin gene cru 1 promoter in transformed tobacco: promoter activity during early and late stages of embryogenesis is influenced by cis-acting elements in partially separate regions

To define sequences in the cruciferin gene cru1 promoter of importance for expression, tobacco (Nicotina tabacum L.) plants were transformed with constructs in which the cru1 promoter, in front of the intact cru1 structural gene, was truncated at - 1216, - 974, - 736, - 515, - 306, - 46 and - 17 bp relative to the cap-site. Cru1 expression in tobacco seeds was studied by Northern analysis, Western analysis and in-situ hybridizations. Comparisons of the Northern analysis of RNA from tobacco seeds harvested at 18 d after pollination with the Western analysis of protein from mature seeds showed that the regions between - 974 to - 736 and - 306 to - 46 were important for the expression of cru1 at an early developmental stage, whereas the regions - 736 to - 515 and - 515 to - 306 were important for expression throughout embryogenesis. By investigating the mRNA levels in transgenic seeds at different stages of development, indications were obtained that the two latter regions exerted their effects during the later stages. The in-situ hybridization showed that cru1 mRNA was distributed in parenchyma cells throughout the embryo in seeds expressing constructs - 974 and - 736. Constructs - 515 and - 306 showed an expression restricted to the axis or axis and parts of the cotyledons. Sequence comparisons of the cru1 promoter with other storage-protein gene promoters, identified several motifs implicated in gene regulation. Gel retardation assays with synthetic oligonucleotides showed that a region present in both cru1 and BnC1 promoters, a CANNTG motif, an SEF3 motif, an abscisic-acid-responsive element and an RY-like motif interacted specifically in vitro with DNA-binding proteins present in nuclear extracts from seeds of Brassica napus L. harvested 40 d after pollination.