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A new family of RhoGEFs activates the Rop molecular switch in plants


In plants, the small GTP-binding proteins called Rops work as signalling switches that control growth, development and plant responses to various environmental stimuli1,2,3. Rop proteins (Rho of plants, Rac-like and AtRac in Arabidopsis thaliana) belong to the Rho family of Ras-related GTP-binding proteins that turn on signalling pathways by switching from a GDP-bound inactive to a GTP-bound active conformation4,5. Activation depends on guanine nucleotide exchange factors (GEFs) that catalyse the otherwise slow GDP dissociation for subsequent GTP binding6. Although numerous RhoGEFs exist in animals and yeasts7, no Rop-specific GEFs have yet been identified in plants and so Rop activation has remained elusive1,2,3,8. Here we describe a new family of RhoGEF proteins that are exclusive to plants. We define a unique domain within these RopGEFs, termed PRONE (plant-specific Rop nucleotide exchanger), which is exclusively active towards members of the Rop subfamily. It increases nucleotide dissociation from Rop more than a thousand-fold and forms a tight complex with nucleotide-free Rop. RopGEFs may represent the missing link in signal transduction from receptor kinases to Rops and their identification has implications for the evolution of the Rho molecular switch.

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Figure 1: Identification of RopGEFs from Arabidopsis thaliana.
Figure 2: The plant RopGEF family.
Figure 3: Functional characterization of PRONE as genuine GEF domain.
Figure 4: RopGEF1 expression and specificity for Rops.


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We thank C. Koerner, T. Mitroshina and D. Kuehlmann for technical assistance; R. Ahmadian for purified Rac1, Cdc42, RhoA, Anti-GST antibodies and for helpful discussions; The Arabidopsis Biological Resource Center for the two-hybrid cDNA library (CD4-30) and pAS2; E. W. Weiler for plant material; K. Unfried and J. Abel for providing the LightCycler, and K. Bierhals for critical reading of the manuscript. This work was supported by the Deutsche Forschungsgemeinschaft. C.T. thanks the Boehringer Ingelheim Fonds for support.

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Correspondence to Antje Berken.

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Competing interests

Accession numbers for the plant RopGEF proteins in Arabidopsis thaliana, Oryza sativa, Medicago truncatula and Lycopersicon esculentum are listed in Fig. 2. Reprints and permissions information is available at The authors declare no competing financial interests.

Supplementary information

Supplementary Figure S1

This figure displays a western blot showing the expression of the bait protein Rop4(D121N) and the prey proteins RopGEF1, RopGEF2 and SpkDHR2 in yeast cells that were tested for two-hybrid interactions. (PDF 85 kb)

Supplementary Figure S2

This figure shows a multiple sequence alignment of RopGEF representatives from different plant species and highlights the central part composed of three highly conserved regions C1, C2 and C3. (PDF 1871 kb)

Supplementary Figure Legends

Full text descriptions to accompany the above Supplementary Figures. (DOC 24 kb)

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Berken, A., Thomas, C. & Wittinghofer, A. A new family of RhoGEFs activates the Rop molecular switch in plants. Nature 436, 1176–1180 (2005).

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