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Specific features of RHO GTPase-dependent signaling in plants
Cell Biology International
Cell Biology International 27 (2003) 191–192
www.elsevier.com/locate/jnlabr/ycbir
Short communication
Specific features of RHO GTPase-dependent signaling in plants ¨ tvo¨s a, D. Szakonyi a, Zs. Kelemen a,b, A ´ . Lendvai a, D. Dorjgotov a, A. Szu¨cs a, K. O c c b a a,* Zs. Po´nya , B. Barnaba´s , S. Brown , D. Dudits , A. Fehe´r a
Institute of Plant Biology, Biological Research Center, HAS, Temesvari krt. 62, 6726 Szeged, Hungary b Institute des Sciences du Vegetal, CNRS, 1 av. de la Terrasse, 91198 Gif-sur-Yvette, France c Agricultural Research Institute, HAS, Brunszvik u. 2, 2462 Martonva´sa´r, Hungary Accepted 15 October 2002
Rho GTPases constitute a major branch of the Ras superfamily of small GTPases. To date, at least 18 mammalian Rho GTPases have been identified, with RHOA, RAC1, and CDC42 being the most intensely studied (Mackay and Hall, 1998). In animal cells, RHO GTPases function as regulated GDP/GTP switches that are activated by diverse extracellular stimuli that stimulate G protein-coupled receptors, receptor tyrosine kinases, integrins, and other cell surface receptors (Kjoller and Hall, 1999). Once activated, each RHO GTPase interacts with a wide spectrum of functionally diverse downstream effectors to initiate cytoplasmic signaling pathways that regulate both cytoplasmic and nuclear events (Aspenstrom, 1999). RHO family GTPases are involved in cellular processes where cell shape is changed due to division, morphogenesis or motility, and require the reorganization of the cytoskeleton (Ridley, 2001). In plants, a specific class of RHO GTPases exists forming the ROP subfamily (Valster et al., 2000). Their roles in polarized growth of pollen tubes (Fu et al., 2001) as well as polarization of Fucus embryos (Belanger and Quatrano, 2000) were hypothesized to be linked to cytoskeletal functions and polarized secretion. RAC/ ROP proteins also induce the activation of the NADPH oxidase enzyme complex leading to superoxide production in mammalian (e.g. macrophages) as well as in plant cells (e.g. Diebold and Bokoch, 2001; Park et al., 2000). However, only limited information has accumulated up to now on the signaling cascades activated by RHO-type GTPases in plants. In our laboratory, we have isolated four different cDNA clones coding for RHO-type GTPases from an alfalfa root-nodule cDNA library. Different mutant * Corresponding author. Tel.: +36-62-432-232; fax: +36-62-433-434. E-mail address: [email protected] (A. Fehe´r).
forms of these proteins have been created by site-specific in vitro mutagenesis. Yeast two-hybrid screens were performed to reveal protein–protein interactions. Screens with the dominant negative form (‘GDP-bound state’) of one of these proteins did not show any specific interaction. In contrast, using the dominant positive form (GTP-bound state) six ‘strong’ interacting partners could be identified including myosin-like proteins, a WD40 protein homologue, and two receptor-like serine/ threonin kinases (RLKs). Further, two-hybrid screens using one of the ROP-interacting RLK protein as bait revealed potential members of a receptor complex, several transcription factors, and proteins implicated in membrane trafficking (endocytosis, Golgi-functions). These results indicate that plant RHO(ROP)-related signaling can, in parallel, reach nuclear as well as cytoplasmic targets such as the cytoskeleton and membranes. Based on these and other published data, one can observe several obvious differences between animal and plant cells concerning RHO GTPase signaling. Plant ROP GTPases form a distinct class and do not belong to the CDC42/RAC/RHO subfamilies: their sequences are divergent from those of their animal counterparts in spite of the high degree of evolutionary conservation of the main functional elements. Interestingly, however, one of the alfalfa RHO proteins identified in our laboratory is distinct from plant RHO(ROP) proteins and is more closely related to animal RAC and CDC42 proteins (Fig. 1). Detailed characterization of this specific plant RHO GTPase is in progress. Concerning regulators and effectors of RHO GTPases, there are characteristic differences between plants and animals: no guanidine nucleotide exchange factors (GEFs) have been identified in plants; plant GTPase activating proteins (GAPs) carry the ‘CRIB’ interaction
1065-6995/03/$ - see front matter 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S1065-6995(02)00335-9
192
D. Dorjgotov et al. / Cell Biology International 27 (2003) 191–192
Acknowledgements The presented research has been supported by the Hungarian National Research Grant ‘OTKA’ T034818 and by a short term NATO Senior Fellowship to A.F. References
Fig. 1. Unrooted phylogenetic tree of four Medicago sativa Rac proteins and representative members of the Rho GTPase protein family. The tree has been made using the BioEdit program package (Hall, 1999). Accession numbers of the used sequences: AtRop1 (AAC78390); HsCdc42 (AAM21109); HsRac1 (P15154); HsRhoA (P06749).
motif while in animal cells this motif is used by the p21-activated kinases (PAKs) to interact with RHO GTPases; in plants small proteins with unknown functions (RICs) carry also the CRIB interaction motif; receptor-like serin/threonine kinases are ROP partners in plants (e.g. they are members of the CLAVATA receptor complex; for review see Clark, 2001) but there are no real PAK homologues (Wu et al., 2001). These observations suggest that although plants and animals use similar RHO-related signaling modules, these are organized in a different way to allow the regulation of specific cellular processes.
Aspenstrom P. Effectors for the Rho GTPases. Curr Opin Cell Biol 1999;11:95–102. Belanger KD, Quatrano RS. Polarity: the role of localized secretion. Curr Opin Plant Biol 2000;3:67–72. Clark SE. Cell signalling at the shoot meristem. Nat Rev Mol Cell Biol 2001;2:276–84. Diebold BA, Bokoch GM. Molecular basis for Rac2 regulation of phagocyte NADPH oxidase. Nat Immunol 2001;2:211–5. Fu Y, Wu G, Yang Z. Rop GTPase-dependent dynamics of tiplocalized F-actin controls tip growth in pollen tubes. J Cell Biol 2001;152:1019–32. Hall TA. BioEdit: a user-friendly biological sequence alignment editor and analysis program for Windows 95/98/NT. Nucl Acids Symp Ser 1999;41:95–8. Kjoller L, Hall A. Signaling to Rho GTPases. Exp Cell Res 1999; 253:166–79. Mackay DJ, Hall A. Rho GTPases. J Biol Chem 1998;273:20685–8. Park J, Choi HJ, Lee S, Lee T, Yang Z, Lee Y. Rac-related GTP-binding protein in elicitor-induced reactive oxygen generation by suspension-cultured soybean cells. Plant Physiol 2000;124: 725–32. Ridley AJ. Rho family proteins: coordinating cell responses. Trends Cell Biol 2001;11:471–7. Valster AH, Hepler PK, Chernoff J. Plant GTPases: the Rhos in bloom. Trends Cell Biol 2000;10:141–6. Wu G, Gu Y, Li S, Yang Z. A genome-wide analysis of Arabidopsis Rop-interactive CRIB motif-containing proteins that act as Rop GTPase targets. Plant Cell 2001;13:2841–56.
Cell Biology International 27 (2003) 191–192
www.elsevier.com/locate/jnlabr/ycbir
Short communication
Specific features of RHO GTPase-dependent signaling in plants ¨ tvo¨s a, D. Szakonyi a, Zs. Kelemen a,b, A ´ . Lendvai a, D. Dorjgotov a, A. Szu¨cs a, K. O c c b a a,* Zs. Po´nya , B. Barnaba´s , S. Brown , D. Dudits , A. Fehe´r a
Institute of Plant Biology, Biological Research Center, HAS, Temesvari krt. 62, 6726 Szeged, Hungary b Institute des Sciences du Vegetal, CNRS, 1 av. de la Terrasse, 91198 Gif-sur-Yvette, France c Agricultural Research Institute, HAS, Brunszvik u. 2, 2462 Martonva´sa´r, Hungary Accepted 15 October 2002
Rho GTPases constitute a major branch of the Ras superfamily of small GTPases. To date, at least 18 mammalian Rho GTPases have been identified, with RHOA, RAC1, and CDC42 being the most intensely studied (Mackay and Hall, 1998). In animal cells, RHO GTPases function as regulated GDP/GTP switches that are activated by diverse extracellular stimuli that stimulate G protein-coupled receptors, receptor tyrosine kinases, integrins, and other cell surface receptors (Kjoller and Hall, 1999). Once activated, each RHO GTPase interacts with a wide spectrum of functionally diverse downstream effectors to initiate cytoplasmic signaling pathways that regulate both cytoplasmic and nuclear events (Aspenstrom, 1999). RHO family GTPases are involved in cellular processes where cell shape is changed due to division, morphogenesis or motility, and require the reorganization of the cytoskeleton (Ridley, 2001). In plants, a specific class of RHO GTPases exists forming the ROP subfamily (Valster et al., 2000). Their roles in polarized growth of pollen tubes (Fu et al., 2001) as well as polarization of Fucus embryos (Belanger and Quatrano, 2000) were hypothesized to be linked to cytoskeletal functions and polarized secretion. RAC/ ROP proteins also induce the activation of the NADPH oxidase enzyme complex leading to superoxide production in mammalian (e.g. macrophages) as well as in plant cells (e.g. Diebold and Bokoch, 2001; Park et al., 2000). However, only limited information has accumulated up to now on the signaling cascades activated by RHO-type GTPases in plants. In our laboratory, we have isolated four different cDNA clones coding for RHO-type GTPases from an alfalfa root-nodule cDNA library. Different mutant * Corresponding author. Tel.: +36-62-432-232; fax: +36-62-433-434. E-mail address: [email protected] (A. Fehe´r).
forms of these proteins have been created by site-specific in vitro mutagenesis. Yeast two-hybrid screens were performed to reveal protein–protein interactions. Screens with the dominant negative form (‘GDP-bound state’) of one of these proteins did not show any specific interaction. In contrast, using the dominant positive form (GTP-bound state) six ‘strong’ interacting partners could be identified including myosin-like proteins, a WD40 protein homologue, and two receptor-like serine/ threonin kinases (RLKs). Further, two-hybrid screens using one of the ROP-interacting RLK protein as bait revealed potential members of a receptor complex, several transcription factors, and proteins implicated in membrane trafficking (endocytosis, Golgi-functions). These results indicate that plant RHO(ROP)-related signaling can, in parallel, reach nuclear as well as cytoplasmic targets such as the cytoskeleton and membranes. Based on these and other published data, one can observe several obvious differences between animal and plant cells concerning RHO GTPase signaling. Plant ROP GTPases form a distinct class and do not belong to the CDC42/RAC/RHO subfamilies: their sequences are divergent from those of their animal counterparts in spite of the high degree of evolutionary conservation of the main functional elements. Interestingly, however, one of the alfalfa RHO proteins identified in our laboratory is distinct from plant RHO(ROP) proteins and is more closely related to animal RAC and CDC42 proteins (Fig. 1). Detailed characterization of this specific plant RHO GTPase is in progress. Concerning regulators and effectors of RHO GTPases, there are characteristic differences between plants and animals: no guanidine nucleotide exchange factors (GEFs) have been identified in plants; plant GTPase activating proteins (GAPs) carry the ‘CRIB’ interaction
1065-6995/03/$ - see front matter 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S1065-6995(02)00335-9
192
D. Dorjgotov et al. / Cell Biology International 27 (2003) 191–192
Acknowledgements The presented research has been supported by the Hungarian National Research Grant ‘OTKA’ T034818 and by a short term NATO Senior Fellowship to A.F. References
Fig. 1. Unrooted phylogenetic tree of four Medicago sativa Rac proteins and representative members of the Rho GTPase protein family. The tree has been made using the BioEdit program package (Hall, 1999). Accession numbers of the used sequences: AtRop1 (AAC78390); HsCdc42 (AAM21109); HsRac1 (P15154); HsRhoA (P06749).
motif while in animal cells this motif is used by the p21-activated kinases (PAKs) to interact with RHO GTPases; in plants small proteins with unknown functions (RICs) carry also the CRIB interaction motif; receptor-like serin/threonine kinases are ROP partners in plants (e.g. they are members of the CLAVATA receptor complex; for review see Clark, 2001) but there are no real PAK homologues (Wu et al., 2001). These observations suggest that although plants and animals use similar RHO-related signaling modules, these are organized in a different way to allow the regulation of specific cellular processes.
Aspenstrom P. Effectors for the Rho GTPases. Curr Opin Cell Biol 1999;11:95–102. Belanger KD, Quatrano RS. Polarity: the role of localized secretion. Curr Opin Plant Biol 2000;3:67–72. Clark SE. Cell signalling at the shoot meristem. Nat Rev Mol Cell Biol 2001;2:276–84. Diebold BA, Bokoch GM. Molecular basis for Rac2 regulation of phagocyte NADPH oxidase. Nat Immunol 2001;2:211–5. Fu Y, Wu G, Yang Z. Rop GTPase-dependent dynamics of tiplocalized F-actin controls tip growth in pollen tubes. J Cell Biol 2001;152:1019–32. Hall TA. BioEdit: a user-friendly biological sequence alignment editor and analysis program for Windows 95/98/NT. Nucl Acids Symp Ser 1999;41:95–8. Kjoller L, Hall A. Signaling to Rho GTPases. Exp Cell Res 1999; 253:166–79. Mackay DJ, Hall A. Rho GTPases. J Biol Chem 1998;273:20685–8. Park J, Choi HJ, Lee S, Lee T, Yang Z, Lee Y. Rac-related GTP-binding protein in elicitor-induced reactive oxygen generation by suspension-cultured soybean cells. Plant Physiol 2000;124: 725–32. Ridley AJ. Rho family proteins: coordinating cell responses. Trends Cell Biol 2001;11:471–7. Valster AH, Hepler PK, Chernoff J. Plant GTPases: the Rhos in bloom. Trends Cell Biol 2000;10:141–6. Wu G, Gu Y, Li S, Yang Z. A genome-wide analysis of Arabidopsis Rop-interactive CRIB motif-containing proteins that act as Rop GTPase targets. Plant Cell 2001;13:2841–56.