Regulation of an embryogenic carrot gene (DC 2.15) and identification of its active promoter sites.

According to previous studies the expression of the gene DC 2.15 is induced in cultured carrot cells after a transfer to an auxin-free medium, where somatic embryo development occurs. This embryogenic gene encodes a prolinerich protein, which resembles proteins involved in auxin-controlled developmental processes. To understand the mechanism underlying the regulation of DC 2.15, an experimental approach has been employed which allows the direct identification of the DC 2.15 promoter structure by applying PCR techniques. We demonstrate the presence of five distinct promoter sequences highly similar in structure, but slightly different in a common region of about 15 nucleotides, which contain the binding site for the GATA factor originally found in the human HOX gene. Activity of each promoter structure was assessed in developing somatic embryos containing the specific sequence fused to the beta-glucuronidase (GUS) reporter gene. For two of the five promoter structures a drastic increase in activity was registered during the torpedo stage while the remaining three were inactive throughout the stages of somatic embryogenesis.