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Identification of mutants in metabolically regulated gene expression

Authors

  • Thomas Martin,

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    • The first two authors have contributed equally to the work.

    • Present address: Division of Biochemistry and Molecular Biology, University of Glasgow, Glasgow G12 8QQ, UK.

  • Hanjo Hellmann,

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    • The first two authors have contributed equally to the work.

    • §

      New address: Institut für Botanik, Eberhard-Karls-Universität Tübingen, Auf der Morgenstelle 1, D-172076 Tübingen, Germany.

  • Renate Schmidt,

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    • Present address: Max-Delbrück-Laboratorium in der Max-Planck-Gesellschaft, Carl von Linné Weg 10, 50829 Köln, Germany.

  • Lothar Willmitzer,

    1. Institut für Genbiologische Forschung, Ihnestr. 63, D-14195 Berlin, Germany
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  • Wolf B. Frommer

    Corresponding author
      *For correspondence (fax +49 7071 29 3287).
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    • §

      New address: Institut für Botanik, Eberhard-Karls-Universität Tübingen, Auf der Morgenstelle 1, D-172076 Tübingen, Germany.


*For correspondence (fax +49 7071 29 3287).

Abstract

Sucrose is the main transported form of assimilates, but, significantly, it also regulates a variety of processes such as photosynthesis and carbon or nitrogen storage. The effects of high sucrose levels are mediated directly by modulation of gene expression. The regulation of storage protein accumulation, here patatin from potato tubers, was used as a model system to study sucrose mediated signal transduction. The transcriptional regulation of patatin genes is conserved in transgenic Arabidopsis, as shown by the analysis of expression of two classes of patatin promoters fused to uidA. Two distinctly different patterns of gene expression were observed. In roots, class I promoter expression is strongly dependent on the exogenous supply of sugars. 3-O-methylglucose induction indicates that the sensor is located upstream of hexokinase. In contrast, the class II promoter is constitutively active in root tips and hydatodes. The progeny of a homozygous class I line was mutagenized with ethyl methane sulphonate and screened for signal transduction mutants using a non-destructive screening system for GUS activity. Four mutants showing reduced sucrose responses (rsr) and two mutants with modified expression patterns (mep) regarding the root tip were identified. In backcross analyses, it was shown that rsr1-1 carries a recessive trans mutation whereas rsr4-1 seems to be a semi-dominant trans mutation in sugar-mediated gene regulation.

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