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G-protein-coupled receptors (GPCRs) are a large family of eukaryotic membrane-spanning proteins that convert signals from the outside of a cell to an appropriate response inside the cell. GPCRs typically associate with a heterotrimeric Gαβγ protein. Activated receptors propagate signals by causing the Gα subunit of the heterotrimer to release GDP and to bind GTP. GTP binding causes a conformational...
Rho GTPases play central roles in the regulation of essential cellular processes, such as directional expansion, motility, and division. RhoGEFs (Guanine Nucleotide Exchange Factors) have key functions in the stimulus-induced spatio-temporal control of Rho GTPase activity. RhoGAPs (GTPase activating proteins) and RhoGDIs (Guanine nucleotide dissociation inhibitors) have long been seen as less important...
Rho-related small guanine nucleotide binding proteins, termed ROP, are important molecular switches that cycle between a GDP-bound “off” and a GTP-loaded “on” state in order to regulate vital signaling pathways in plants. They constitute a unique class within the Rho family with distinctive features, and we are just beginning to understand the mode of action, the specificities, and molecular mechanisms...
ROP/RAC GTPases and heterotrimeric G protein are soluble proteins that function at cellular membranes, primarily the plasma membranes. Attachment to the membrane takes place by virtue of the posttranslational lipid modifications: prenylation, S-acylation, and N-myristoylation, as well as by lysine and arginine-rich positively charged domain, referred to as polybasic region. The lipid modifications...
Plant Rho-family GTPases, named ROPs (Rho-like GTPases from plants), like their counterparts in fungi and animals, have the conserved function in the regulation of the cytoskeleton, a fundamental dynamic cellular structure important for the regulation of plant growth, development, and responses to the environment. In the regulation of the cytoskeleton, ROP signaling pathways involve specific regulators...
Mounting evidence supports that RAC/ROP GTPases are central regulators for diverse signaling pathways for plant growth, development, and interactions with the environment. Their regulatory activities for key intracellular process, such as control of actin dynamics, membrane trafficking, and several hormone signal transduction pathways, suggest inevitable functional roles for RAC/ROPs in regulating...
Deficient mutants of the heterotrimeric G protein α subunit (Gα) gene in rice (d1) showed several characteristic phenotypes, such as erect and shortened leaves, shortened internodes, and shortened seeds. The characteristics of ten alleles of d1 are summarized in this chapter. Sensitivity of d1 to seven plant hormones (auxin, abscisic acid, gibberellin, cytokinin, brassinosteroid, ethylene, and jasmonate)...
Auxin is the earliest-discovered hormone in higher plants. It regulates many aspects of plant growth and development through its biosynthesis, polar transport, and signaling transduction. In the 1970s, brassinosteroids (BRs) were discovered from pollen of brassica plants and identified as functioning hormones. The function of BRs at the cellular level is mainly promoting cell elongation and differentiation...
The heterotrimeric GTP-binding protein (G-protein) complex is a conserved signaling module found in all eukaryotes. G-proteins function as molecular switches to regulate diverse signal transduction pathways. Although in contrast to its counterpart in mammals, the repertoire of G-protein complex in plants is much simpler, G-proteins play important roles in plant development, hormonal signaling, and...
Fine-tuned regulation of stomatal aperture size is key to the survival of land plants. This chapter discusses the roles of heterotrimeric G proteins in the regulation of stomatal movements and ion channel activities of guard cells. Evidence implicating heterotrimeric G protein function in light-induced stomatal opening, ABA-induced stomatal closure, and pathogen-induced stomatal movements is described...
MLO proteins are structurally reminiscent of G-protein-coupled receptors but act independently of heterotrimeric G-proteins as major susceptibility factors to powdery mildew fungi. In barley, monomeric RAC/ROPs, instead of heterotrimeric G-proteins, MLO-dependently modulate susceptibility to powdery mildew, which may involve functions in cytoskeleton remodeling. In contrast to the role of RAC/ROPs...
Under the peaceful appearance of lovely green meadow, the different plant communities are engaged in a continuous struggle for life. Plants use every imaginable mechanism to enhance their defenses in order to survive attacks from an enormous number of pathogens. Plant innate immunity strongly relies on signal transduction pathways connecting pathogen recognition with the establishment of specific...
Seven-transmembrane receptors (7TMRs; also known as G protein-coupled receptors, GPCRs) constitute the largest receptor superfamily in metazoa. In striking contrast, very few numbers of 7TMRs are reported in plants. Comparative analysis revealed that many of 7TMR proteins found in plants are in fact unique to the plant kingdom. More interestingly, some 7TMR proteins appear to have acquired GPCR functions...
G proteins, including monomeric G proteins and heterotrimeric G proteins composed of Gα, Gβ, and Gγ subunits, are molecular switches in cellular signaling. In addition to these classic G proteins, plants have several types of unconventional G proteins, such as extra-large G proteins (XLGs), developmentally regulated G proteins (DRGs), and GPCR-type G proteins (GTGs). XLGs are nuclear-localized proteins...
The core ROP GTPase module is composed of ROP along with regulators that directly influence its activity. This module plays an important role in several crucial cellular pathways in plants, such as polarized cell growth and pathogen response. ROP’s ability to influence multiple pathways likely derives from the complexity of the module components (e.g., the ROP regulators PRONE GEF, and RopGAP), which...
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