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Plant Cell Advance Online Publication
Published on October 15, 2002; 10.1105/tpc.006320

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Received July 15, 2002
Accepted September 5, 2002

Plant Rac-Like GTPases Are Activated by Auxin and Mediate Auxin-Responsive Gene Expression

Li-zhen Tao 1, Alice Y. Cheung 2*, and Hen-ming Wu 3

1 Department of Biochemistry and Molecular Biology, University of Massachusetts, Amherst, Massachusetts 01003
2 Department of Biochemistry and Molecular Biology, University of Massachusetts, Amherst, Massachusetts 01003; Molecular and Cellular Biology Graduate Program, University of Massachusetts, Amherst, Massachusetts 01003; Plant Biology Graduate Program, University of Massachusetts, Amherst, Massachusetts 01003
3 Department of Biochemistry and Molecular Biology, University of Massachusetts, Amherst, Massachusetts 01003; Molecular and Cellular Biology Graduate Program, University of Massachusetts, Amherst, Massachusetts 01003

* To whom correspondence should be addressed. E-mail: acheung{at}biochem.umass.edu.

The auxin indole-3-acetic acid is a key plant hormone essential for a broad range of growth and developmental processes. Here, we show that auxin activates Rac-like GTPases (referred to as Rac/Rop GTPases), and they in turn stimulate auxin-responsive gene expression. In particular, we show that overexpressing a wild-type tobacco Rac/Rop GTPase, NtRac1, and its constitutively active mutant form activates auxin-responsive gene expression. On the other hand, overexpressing dominant-negative NtRac1 and Rac-negative regulators, or reducing the endogenous NtRac1 level, suppresses auxin-induced gene expression. Furthermore, overexpression of NtRac1 activity or suppression of its expression in transgenic seedlings induces phenotypes that are similar to auxin-related defects. Together, our results show that a subset of plant Rac/Rop GTPases functions in mediating the auxin signal to downstream responsive genes.






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