Abstract
Heterotrimeric G-proteins regulate multiple aspects of plant growth, development, and response to biotic and abiotic stresses. While the core components of heterotrimeric G-proteins and their basic biochemistry are similar in plants and metazoans, key differences exist in their regulatory mechanisms. In particular, the activation mechanisms of plant G-proteins appear diverse and may include both canonical and novel modes. Classical G-protein-coupled receptor-like proteins exist in plants and interact with Gα proteins, but their ability to activate Gα by facilitating GDP to GTP exchange has not been demonstrated. Conversely, there is genetic and functional evidence that plant G-proteins interact with the highly prevalent receptor-like kinases (RLKs) and are phosphorylated by them. This suggests the exciting scenario that in plants the G-proteins integrate RLK-dependent signal perception at the plasma membrane with downstream effectors. Because RLKs are active kinases, it is also likely that the activity of plant G-proteins is regulated via phosphorylation/dephosphorylation rather than GTP–GDP exchange as in metazoans. This review discusses our current knowledge of the possible RLK-dependent regulatory mechanisms of plant G-protein signaling in the context of several biological systems and outlines the diversity that might exist in such regulation.
Highlights
Heterotrimeric G-proteins are signal transducers present at the plasma membrane of eukaryotic cells.The core heterotrimeric G-protein complex (G-proteins, hereafter) comprises three dissimilar subunits, Gα, Gβ, and Gγ
While the core components of heterotrimeric G-proteins and their basic biochemistry are similar in plants and metazoans, key differences exist in their regulatory mechanisms
Classical G-protein-coupled receptorlike proteins exist in plants and interact with Gα proteins, but their ability to activate Gα by facilitating GDP to GTP exchange has not been demonstrated
Summary
Heterotrimeric G-proteins are signal transducers present at the plasma membrane of eukaryotic cells.The core heterotrimeric G-protein complex (G-proteins, hereafter) comprises three dissimilar subunits, Gα, Gβ, and Gγ. The expression of a phosphomimic version of RGS protein in nod mutant background restores nodule formation, at least partially (Roy Choudhury and Pandey, 2015).This supports the notion that at least one role of NFR1 is to phosphorylate RGS proteins, which allow successful nodulation by deactivating the Gα proteins (Fig. 1B) While this model explained how the Gα proteins are maintained in their inactive conformation during nodulation, the RLK-dependent regulation was indirect. Such a scenario would allow for the inactivation of the negative regulator (Gα) and signaling by the positive regulators (Gβγ), resulting in successful nodulation While this mechanism does not exactly address the ‘activation’ of G proteins, it certainly uncovers a yet-unexplored signaling scheme via plant G-proteins and RLKs in which the trimer is dissociated as a result of receptor activation.The roles of XLGs have not been examined in nodule signaling and development to date. XLG proteins interact with RLKs and are known phosphoproteins.it may represent an additional regulatory mechanism for plant G-protein signaling and warrants further exploration
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