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Development 129, 2797-2806 (2002)
© 2002 The Company of Biologists Limited

Transformation of shoots into roots in Arabidopsis embryos mutant at the TOPLESS locus

Jeff A. Long1,3, Scott Woody1, Scott Poethig2, Elliot M. Meyerowitz3 and M. Kathryn Barton1,*,{dagger}

1 Department of Genetics and Program in Cellular and Molecular Biology, University of Wisconsin-Madison, Madison, WI, USA
2 Department of Biology, University of Pennsylvania, Philadelphia, PA, USA
3 Division of Biology, California Institute of Technology, Pasadena, CA, USA
* Present address: Department of Plant Biology, Carnegie Institution of Washington, 260 Panama Street, Stanford, CA 94305, USA

{dagger}Author for correspondence (e-mail: barton{at}andrew2.stanford.edu)

Accepted 19 March 2002

We describe a novel phenotype in Arabidopsis embryos homozygous for the temperature-sensitive topless-1 mutation. This mutation causes the transformation of the shoot pole into a root. Developing topless embryos fail to express markers for the shoot apical meristem (SHOOT MERISTEMLESS and UNUSUAL FLORAL ORGANS) and the hypocotyl (KNAT1). By contrast, the pattern of expression of root markers is either duplicated (LENNY, J1092) or expanded (SCARECROW). Shifts of developing topless embryos between permissive and restrictive temperatures show that apical fates (cotyledons plus shoot apical meristem) can be transformed to basal fates (root) as late as transition stage. As the apical pole of transition stage embryos shows both morphological and molecular characteristics of shoot development, this demonstrates that the topless 1 mutation is capable of causing structures specified as shoot to be respecified as root. Finally, our experiments fail to show a clear link between auxin signal transduction and topless-1 mutant activity: the development of the apical root in topless mutant individuals is not dependent on the activity of the predicted auxin response factor MONOPTEROS nor is the expression of DR5, a proposed ‘auxin maximum reporter’, expanded in the apical domain of topless embryos.

Key words: Arabidopsis, TOPLESS, Shoot transformation, Embryogenesis, Polarity






© The Company of Biologists Ltd 2002