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Plant Physiol, December 2000, Vol. 124, pp. 1625-1636
Arabidopsis RopGAPs Are a Novel Family of Rho GTPase-Activating
Proteins that Require the Cdc42/Rac-Interactive Binding Motif for
Rop-Specific GTPase Stimulation1
Guang
Wu,
Hai
Li, and
Zhenbiao
Yang*
Department of Botany and Plant Sciences, University of California,
Riverside, California 92521 (G.W., Z.Y.); Department of Plant Biology,
Ohio State University, Columbus, Ohio 43210 (G.W.); and Plant Molecular
Biology Laboratory, Salk Institute, San Diego, California 92186 (H.L.)
The plant-specific Rop subfamily of Rho GTPases, most closely
related to the mammalian Cdc42 and Rac GTPases, plays an important role
in the regulation of calcium-dependent pollen tube growth, H2O2-mediated cell death, and many other
processes in plants. In a search for Rop interactors using the
two-hybrid method, we identified a family of Rho GTPase-activating
proteins (GAP) from Arabidopsis, termed RopGAPs. In addition to a GAP
catalytic domain, RopGAPs contain a Cdc42/Rac-interactive binding
(CRIB) motif known to allow Cdc42/Rac effector proteins to bind
activated Cdc42/Rac. This novel combination of a GAP domain with a CRIB
motif is widespread in higher plants and is unique to the regulation of
the Rop GTPase. A critical role for CRIB in the regulation of in vitro
RopGAP activity was demonstrated using point and deletion mutations. Both types of mutants have drastically reduced capacities to stimulate the intrinsic Rop GTPase activity and to bind Rop. Furthermore, RopGAPs
preferentially stimulate the GTPase activity of Rop, but not Cdc42 in a
CRIB-dependent manner. In vitro binding assays show that the RopGAP
CRIB domain interacts with GTP- and GDP-bound forms of Rop, as well as
the transitional state of Rop mimicked by aluminum fluoride. The CRIB
domain also promotes the association of the GAP domain with the
GDP-bound Rop, as does aluminum fluoride. These results reveal a novel
CRIB-dependent mechanism for the regulation of the plant-specific
family of Rho GAPs. We propose that the CRIB domain facilitates the
formation of or enhanced GAP-mediated stabilization of the transitional
state of the Rop GTPase.
1
This work was supported by the National Science
Foundation (grant no. MCB-S9724047 to Z.Y.).
*
Corresponding author; e-mail zhenbiao.yang{at}ucr.edu; fax
909-787-4437.
© 2000 American Society of Plant Physiologists
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