Sequence and expression of a phylogenetically conserved carrot gene, Dc3 : a marker of embryogenic potential /
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| Other Authors: | , , |
| Format: | Thesis Book |
| Language: | English |
| Published: |
1989.
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| Subjects: | |
| Online Access: | Link to OAKTrust copy |
| Abstract: | Dc3 is a cDNA derived from mRNA encoded by a member of a small gene family expressed during carrot embryogenesis. It is highly expressed in carrot embryogenic tissue but only slightly expressed in callus tissue. There are no detectable Dc3 transcripts in leaf or other somatic tissues. A genomic clone, DcG3, was identified by hybridization with the Dc3 cDNA. Primer extension mapping and sequence analysis of both the Dc3 genomic recombinant and Dc3 cDNA defined the DcG3 transcription unit which includes one intron. The predicted amino acid sequence is 163 residues in length and possesses a highly conserved tandem direct repeat of 50 amino acids. Within these two elements are ten unusual repeat charge structures of the form (..+-+..) termed KEK boxes due to the charged constituent amino acids. Transgenic tobacco plants containing the DcG3 promoter cloned 5' to a β-glucuronidase (GUS) reporter gene demonstrate embryo and endosperm expression in seed. Expression in tobacco endosperm tissue exhibits radial polarity. GUS activity was undetectable in any other transgenic tobacco tissue maintained under normal growth conditions. Carrot tissue transformed with the same DcG3 promoter/GUS construction expressed GUS in the protoderm of somatic embryos. Chemical agents known to affect plant embryogenesis were examined for effects on Dc3 driven GUS expression. Anti-oxidants and ABA strongly enhance Dc3 driven GUS expression in carrot embryogenic and suspension cultures. Additional GUS constructs demonstrated enhancer activity of the upstream sequences operable in both carrot somatic embryos and tobacco zygotic embryos. Dc3-like sequences are detectable in other dicot and monocot plant genomic DNAs by hybridization. Amino acid sequence homologies to cotton, barley and rape late embryogenesis abundant (lea) genes suggest that Dc3 may be a carrot lea gene involved in seed dessication and perhaps other water stress responses. Dc3 and lea-type proteins are distinguishable from other plant sequences by an overall protein index called flexibility. This index is found to be highest for the lea-type proteins and probably reflects a compositional bias that is unusual for other proteins. Thus Dc3 possesses an interesting amino acid sequence and is phylogenetically conserved together with trans-acting factors required for its tissue specific expression in carrot somatic embryos and in the zygotic embryo and endosperm of tobacco. |
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| Item Description: | Typescript (photocopy). Vita. "Major subject: Biology." |
| Physical Description: | ix, 118 leaves : illustrations ; 29 cm |
| Bibliography: | Includes bibliographical references. |