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  • 1
    ISSN: 1573-5028
    Keywords: ABA ; abi mutants ; drought ; homeodomain ; leucine zipper ; transcription factor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Homeodomain-leucine zipper (HD-Zip) proteins are transcription factors as yet found only in plants. We have characterized one HD-Zip gene, ATHB6, from Arabidopsis thaliana. ATHB6 was expressed constitutively in seedlings, but significantly up-regulated in seedlings subjected to water deficit, osmotic stress or exogenous treatment with abscisic acid (ABA), an induction being detectable within 30 min. The ATHB6 induction was impaired in the two ABA-insensitive mutants, abi1 and abi2, but unaffected in the abi3 mutation. The induction was ABA-dependent, since no increase in ATHB6 transcript was detected in the ABA-deficient mutant aba-3 subjected to drought treatment. These results suggest that ATHB6 may act downstream to both ABI1 and ABI2 in a signal transduction pathway mediating a drought stress response. A translational fusion of the ATHB6 promoter with the reporter gene GUS (ATHB6::GUS) in transgenic A. thaliana plants showed high-level expression in leaf primordia. Expression in developing cotyledons, leaves, roots and carpels was restricted to regions of cell division and/or differentiation. The expression in the cotyledons was detectable in the epidermis and high in the stomatal cells. In mature cotyledons and leaves the marker gene was expressed only in the vascular tissue. These expression data suggest ATHB6 to have a function related to cell division and/or differentiation in developing organs.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-5028
    Keywords: cDNA ; development ; homeobox ; in situ hybridization ; transcription factor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A recently discovered class of genes in Arabidopsis thaliana encode putative transcription factors which contain a homeodomain closely linked to a leucine zipper motif. We have previously reported on the cloning and cDNA sequence of one gene of this class, Athb-3. In this article we show this gene to be expressed predominantly in the cortex of the root and the stem. Using the Athb-3 clone as a probe we have isolated cDNA clones corresponding to three novel homeodomain-leucine zipper proteins. These clones, Athb-5, Athb-6 and Athb-7, hybridized to transcripts that were relatively abundant in the leaf, but also present in other vegetative organs, as well as in the flower. Only weak hybridization was observed to seed pod samples. These observations indicate that these Athb genes have major functions in the mature plant, and therefore, in contrast to homeobox genes in other eukaryotes and to the kn-1 gene in maize, are unlikely to function in the primary control of developmental processes during embryogenesis or organogenesis. The deduced amino acid sequences of Athb-5, Athb-6 and Athb-7 are highly similar to the previously isolated Athb-1, Athb-2 and Athb-3 in the homeodomain and leucine-zipper parts of the proteins, whereas the similarities to homeodomain proteins from other eukaryotes are limited. The Athb proteins,thus constitute a new and well defined class of homeodomain proteins, apparently unique to plants.
    Type of Medium: Electronic Resource
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