DEVELOPMENTAL GENETICS 11:65-76 (1990) Molecular Analysis of a Phylogenetically Conserved Carrot Gene: Developmental and Environmental Regulation

ABSTRACT Extensive studies of gene ex-pression programs in carrot somatic embryos iden-tified a gene, designated Dc3, that serves as a re-liable molecular marker for the acquisition of embryogenic potential by carrot cells in culture. The complete sequence of a carrot genomic re-gion, DcG3, encoding a Dc3-like mRNA, was de-termined. The DcG3 transcription unit contains a single intron and encodes mRNA that is expressed at high levels in embryonic tissue but is undetect-able in somatic tissue of carrot. The predicted pro-tein sequence of DcG3 is 163 amino acids and includes two approximately 50 amino acid direct repeats which in turn include additional repetitive elements with an unusual distribution of charged amino acids. Dc3 and Dc3-like mRNAs are en-coded by a small divergent gene family. Further-more, similarities of the Dc3 gene family with genes from other plant species that are expressed in re-sponse to environmental and developmental cues suggest a possible role in seed desiccation and possibly in more general water-stress responses in plants. Analysis of transgenic tobacco containing a p-glucuronidase (GUS) reporter gene fused to a 1.7 kb 5 ' upstream element of DcG3 defined a promoter/enhancer complex that confers develop-mentally and environmentally regulated expression of GUS activity. Thus, DcG3 is phylogenetically conserved together with the frans-acting factors re-quired for its regulated expression in transgenic to-bacco. Key words: Somatic embryogenesis, gene regu-lation, transgenic plants, p-glucuronidas