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  • 1
    ISSN: 1617-4623
    Keywords: Plant hormone ; Mutant ; Arabidopsis ; Auxin ; Plant development
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We have screened a large population of M2 seeds ofArabidopsis thaliana for plants which are resistant to exogenously applied indole-acetic acid (IAA). One of the resistant lines identified in this screen carries a dominant mutation which we have namedaxr2. Linkage analysis indicates that theaxr2 gene lies on chromosome 3. Plants carrying theaxr2 mutation are severe dwarfs and display defects in growth orientation of both the shoot and root suggesting that the mutation affects some aspect of gravitropic growth. In addition, the roots ofaxr2 plants lack root hairs. Growth inhibition experiments indicate that the roots ofaxr2 plants are resistant to ethylene and abscisic acid as well as auxin.
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  • 2
    ISSN: 1617-4623
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary An activity variant in Drosophila, Ddc +4, which has been isolated from natural populations is shown to affect the level of messenger RNA for dopa decarboxylase (DDC) in a stage specific manner. Newly hatched first instar larvae and newly eclosed adults have 1.5 times the amount of DDC mRNA as the Canton-S laboratory strain. On the other hand, puparia of the variant have only 0.5 times as much DDC mRNA as Canton-S. Genomic Southern analysis revealed that Ddc +4 DNA differed from Canton-S DNA by four small restriction length polymorphisms. To confirm these differences, a library of Ddc +4 was constructed in the λ1059 vector. A clone was recovered spanning the DDC region and compared to cloned Canton-S DNA. Acrylamide gel electrophoresis of restriction fragments revealed that one previously identified insertion really consisted of two smaller ones. One of the other differences identified by the Southern analysis was not confirmed in the cloned DNA of Ddc +4, indicating some divergence had occurred in the variant strain between the time of its isogenization and cloning. The differences between the cloned Ddc +4 DNA and cloned Canton-S DNA consisted of six small restriction length polymorphisms and one restriction site polymorphism. Five of the seven differences lay in the 5′ untranslated leader sequence of the DDC mRNA or in the 4.5 kb of DNA upstream of the transcription start site. The existence of these small (〈100 bp) insertion/deletion polymorphisms in a strain exhibiting a complex temporal phenotype for DDC activity, suggests natural populations are an excellent source of variation affecting gene expression. Secondly, subtle restriction length polymorphisms near the 5′ end of genes may well be an important component of the variation upon which selection might be expected to act.
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  • 3
    ISSN: 1617-4623
    Keywords: Auxin resistance ; 2,4-Dichloro phenoxyacetic acid ; Phytohormone ; Plant development ; Herbicide-resistance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Mutant lines of Arabidopsis thaliana resistant to the artificial auxin 2,4-dichloro phenoxyacetic acid (2,4-D) were isolated by screening for growth of seedlings in the presence of toxic levels of 2,4-D. Genetic analysis of these resistant lines indicated that 2,4-D resistance is due to a recessive mutation at a locus we have designated Axr-1. Mutant seedlings were resistant to approximately 50-fold higher concentrations of 2,4-D than wild-type and were also resistant to 8-fold higher concentrations of indole-3-acetic acid (IAA) than wild-type. Labelling studies with (14C)2,4-D suggest that resistance was not due to changes in uptake or metabolism of 2,4-D. In addition to auxin resistance the mutants have a distinct morphological phenotype including alterations of the roots, leaves, and flowers. Genetic evidence indicates that both auxin resistance and the morphological changes are due to the same mutation. Because of the pleiotropic morphological effects of these mutations the Axr-1 gene may code for a function involved in auxin action in all tissues of the plant.
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  • 4
    ISSN: 1617-4623
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Measurement of dopa decarboxylase (DDC) levels in 109 strains of Drosophila melanogaster isogenic for second chromosomes isolated independently from natural populations was undertaken. One of the most extreme variants, designated Ddc +4, was shown to have about 20% more DDC activity at adult eclosion than a standard laboratory strain used for comparison. The DDC overproduction was shown to segregate with the second chromosome and was mapped to a position within 0.15 map units of the DDC structural gene. The variant was shown to be an underproducer of DDC activity at pupariation and the genetic element responsible for this trait mapped in an identical fashion to that causing overproduction. The temporal phenotype described above was observed in the epidermis but DDC activity levels in neural tissue were normal. Examination of CRM levels at pupariation and eclosion revealed that altered DDC protein levels were responsible for the variant DDC activity levels. Electrophoretic analysis under both denaturing and non-denaturing conditions indicated that the DDC molecules in Ddc +4 and the laboratory strain were indistinguishable. These results suggest that alterations in a genetic element (or elements) lying in close proximity to the structural gene are responsible for the complex temporal phenotype of DDC activity exhibited in the variant Ddc +4.
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  • 5
    ISSN: 1617-4623
    Keywords: Repetitive DNA ; Arabidopsis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Three members of a family of highly repeated DNA sequences from Arabidopsis thaliana have been cloned and characterized. The repeat unit has an average length of 180 bp and is tandemly repeated in arrays longer than 50 kb. This family represents more than one percent of the Arabidopsis genome. Sequence comparisons with tandemly repeated DNA sequences from other Cruciferae species show several regions of homology and a similar length of the repeat unit. Homologies are also found to highly repeated sequences from other plant species. When the sequence CCGG occurs in the repeated DNA, the inner cytosine is generally methylated.
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  • 6
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The axrl mutation has been mapped to the end of chromosome 1 (ref. 5). To obtain detailed information on the position of axrl, we analysed 126 chromosomes resulting from recombination between axrl and the proximal marker disl for segregation of restriction-fragment length polymorphisms (RFLPs) ...
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  • 7
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Auxin is a pivotal plant hormone that controls many aspects of plant growth and development. Perceived by a small family of F-box proteins including transport inhibitor response 1 (TIR1), auxin regulates gene expression by promoting SCF ubiquitin-ligase-catalysed degradation of the Aux/IAA ...
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  • 8
    Electronic Resource
    Electronic Resource
    [s.l.] : Macmillian Magazines Ltd.
    Nature 435 (2005), S. 441-445 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The plant hormone auxin regulates diverse aspects of plant growth and development. Recent studies indicate that auxin acts by promoting the degradation of the Aux/IAA transcriptional repressors through the action of the ubiquitin protein ligase SCFTIR1. The nature of the signalling ...
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  • 9
    Electronic Resource
    Electronic Resource
    [s.l.] : Macmillian Magazines Ltd.
    Nature 414 (2001), S. 271-276 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The plant hormone auxin is central in many aspects of plant development. Previous studies have implicated the ubiquitin-ligase SCFTIR1 and the AUX/IAA proteins in auxin response. Dominant mutations in several AUX/IAA genes confer pleiotropic auxin-related phenotypes, whereas ...
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  • 10
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 413 (2001), S. 374-375 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] If you're a plant you cannot get by without auxin, for it regulates various essential aspects of growth and development. In their paper on page 425 of this issue, Geldner et al. provide a surprise for biologists studying auxin transport. But their results will also be of wider interest, for ...
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