Small GTPase Signaling in Plant Defense Responses

Small guanosine triphosphatases (GTPases) act as molecular switches that orchestrate the rapid assembly of defence machinery in plants. Members of the Rho, Rac/ROP and Rab families cycle between an inactive GDP-bound state and an active GTP-bound state under the control of guanine-nucleotide exchange factors and GTPase-activating proteins. Once activated by cell‐surface pattern recognition receptors or intracellular nucleotide-binding leucine-rich repeat receptors, these GTPases regulate the production of reactive oxygen species via NADPH oxidases, reorganise the actin cytoskeleton, modulate vesicular trafficking of defence compounds and integrate phytohormone signalling pathways such as salicylic acid and jasmonic acid. Pathogens may subvert GTPase signalling to promote colonisation, while plants evolve scaffold and effector proteins that stabilise GTPase activity at sites of attempted invasion. Advances in structural biology have illuminated the conformational switches that determine GTPase–effector specificity, offering routes to engineer enhanced disease resistance in crops. Collectively, small GTPase signalling constitutes a central hub linking receptor activation to cell-wall reinforcement, antimicrobial metabolite deployment and systemic resistance, with profound implications for sustainable agriculture and food security.

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Small GTPase Signaling in Plant Defense Responses publication trend

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Technical terms

Small GTPase: A monomeric guanine-nucleotide-binding protein that cycles between inactive (GDP-bound) and active (GTP-bound) states to transduce signals.

NADPH oxidase: A membrane-associated enzyme complex that generates reactive oxygen species as part of the oxidative burst in defence.

Reactive oxygen species (ROS): Highly reactive molecules derived from oxygen that function as signalling messengers and antimicrobial agents in plant immunity.

Guanine-nucleotide exchange factor (GEF): A protein that promotes the exchange of GDP for GTP on small GTPases, thereby activating them.

Nucleotide-binding leucine-rich repeat receptor (NLR): An intracellular immune receptor that detects pathogen effectors and initiates downstream defence signalling.

Vesicular trafficking: The intracellular transport of vesicles carrying proteins and metabolites, essential for delivering defence compounds to sites of infection.

References

1. AtRAC7/ROP9 Small GTPase Regulates A. thaliana Immune Systems in Response to B. cinerea Infection. International Journal of Molecular Sciences (2024).
2. Small G Protein StRab5b positively regulates potato resistance to Phytophthora infestans. Frontiers in Plant Science (2023).
3. Cloning and Functional Analysis of CsROP5 and CsROP10 Genes Involved in Cucumber Resistance to Corynespora cassiicola. Biology (2024).
4. Regulation and Functions of ROP GTPases in Plant–Microbe Interactions. Cells (2020).
5. The Crystal Structure of the Plant Small GTPase OsRac1 Reveals Its Mode of Binding to NADPH Oxidase*. Journal of Biological Chemistry (2014).