This volume focuses on the structure, function and regulation of plant signaling G proteins and their function in hormonal pathways, polarity, differentiation, morphogenesis and responses to biotic and abiotic stresses.

Plants are sessile organisms that need to continuously coordinate between external and internal cues. This coordination requires the existence of hubs to allow cross-talk between different signaling pathways. A single family of Rho GTPases, termed either ROPS or RACs, and heterotrimeric G proteins have emerged as the major molecular switches in a multitude of signal transduction pathway in plants.

1;Preface;4 2;Contents;8 3;Plant Ga Structure and Properties;10 3.1;1 Introduction: Structure-function Relationships in G Protein Signaling;11 3.2;2 Comparison of Plant Ga Proteins to Mammalian Ga Proteins;12 3.3;2.1 Switch Regions and the Gbg Interacting Interface;12 3.4;2.2 Guanine Nucleotide-Binding Pocket;16 3.5;2.3 Loop Insertions;17 3.6;2.4 The a5 Helix;17 3.7;2.5 RGS Interacting Interface;18 3.8;2.6 Receptor and Effector Coupling;18 3.9;2.7 Cholera Toxin and Pertussis Toxin;19 3.10;2.8 Contacts Between Ras-like and Helical Domains ( Linkers 1 and 2);19 3.11;2.9 Other Residues of Interest: Tools for Studying G Protein Signaling;19 3.12;2.10 Summary of Structural Comparison Between Plant and Mammalian Ga Proteins;20 3.13;3 Properties of Plant Ga Proteins;20 3.14;3.1 Kinetic Properties of the Arabidopsis Ga Protein;20 3.15;3.2 Kinetic Properties of Other Plant Ga Proteins;21 3.16;3.3 Possible Structural Determinants of Rapid Nucleotide Exchange;22 3.17;3.4 Plant Ga Lipid Modification and Subcellular Localization;22 3.18;3.5 Candidate Plant GPCRs;23 3.19;3.6 Candidate Plant Ga Effectors;25 3.20;3.7 Candidate Effectors in Plants Identified by Homology to Animal Effectors;27 3.21;4 Conclusions: Plant Ga Proteins are like Animal Ga Proteins, but Different;28 3.22;References;29 4;Regulatory and Cellular Functions of Plant RhoGAPs and RhoGDIs;35 4.1;1 Introduction;35 4.2;2 RhoGAP Protein Families;37 4.3;2.1 Plant RhoGAP SubFamily I: CRIB domain proteins;40 4.4;2.2 Plant RhoGAP Subfamily II: PH Domain Proteins;45 4.5;3 RhoGDI Protein Families;47 4.6;3.1 AtROPGDI1: Maintenance of Cellular Polarity Required for Root Hair Initiation and Growth;49 4.7;3.2 NtRhoGDI2: Maintenance of Polarized Rho GTPase Activation at the Tip of Tobacco Pollen Tubes;50 4.8;4 Conclusions;52 4.9;References;53 5;Structure and Function of ROPs and their GEFs;57 5.1;1 Introduction;57 5.2;2 Structure and Function of ROPs;59 5.3;2.1 Structural Characteristics of ROP Proteins;59 5.4;2.2 Nucleotide Binding, GTPase Activity, and Commonly Used Mutants;62 5.5;<;62 5.6;2.3 Plant- and Isoform-Specific Structural Features;63 5.7;3 RopGEFs: Novel Activators for Rho Proteins in Plants;65 5.8;3.1 Identification of RopGEFs;65 5.9;3.2 Architecture of RopGEFs and Mode of Substrate Binding;66 5.10;3.3 Insights into the Catalytic Mechanism of RopGEFs;67 5.11;3.4 Substrate Specificity of RopGEFs;71 5.12;3.5 RopGEFs in the Physiological Context;72 5.13;4 Conclusions;73 5.14;References;73 6;Protein-Lipid Modifications and Targeting of ROP/ RAC and Heterotrimeric G Proteins;78 6.1;1 Introduction;78 6.2;2 The Lipid Modifications 2.1 Prenylation and CaaX Processing;80 6.3;2.2 S-Acylation;82 6.4;2.3 N-Myristoylation;84 6.5;3 Lipid Modifications and Subcellular Targeting of ROPs 3.1 Subcellular Distribution and Function of ROPs;84 6.6;<;84 6.7;3.2 Prenylation of Type-I ROPs;85 6.8;3.3 Transient S-Acylation of Type-I ROPs;86 6.9;3.4 Stable S-Acylation of Type-II ROPs;87 6.10;3.5 Role of the Polybasic Domain for Plasma Membrane Targeting;88 6.11;4 Plasma Membrane Microdomains 4.1 The Lipid Raft Hypothesis;90 6.12;4.2 Accumulation of ROPs in Membrane Microdomains;90 6.13;5 Lipid Modifications and RhoGDI;91 6.14;6 Lipid Modifications and Targeting of Heterotrimeric G Proteins 6.1 Modification of the Ga and Function of Hetertrimeric G Protein in Plants;91 6.15;6.2 Prenylation and S-Acylation of Gg Subunits;92 6.16;7 Conclusions;93 6.17;References;93 7;ROP GTPases and the Cytoskeleton;98 7.1;1 Introduction;98 7.2;2 Regulation of AFs;99 7.3;2.1 Conserved Rho GTPase Downstream Pathways in the Regulation of AFs;100 7.4;2.2 Plant-Specific Players in the ROP-Dependent Regulation of AFs;102 7.5;3 Regulation of Microtubules;104 7.6;4 Crosstalk Between AFs, MTs, and ROPs;105 7.7;5 Conclusion and Perspectives;106 7.8;References;107 8;RAC/ROP GTPases in the Regulation of Polarity and Polar Cell Growth*;112 8.1;1 Introduction;113 8.2;2 RAC/ROP, a Tip-Localized Regulator for the Polarized Pollen Tube