Nucleotides and nucleotide derivatives as signal molecules in plants.

The article focuses on the roles of nucleotides and nucleotide derivatives as signaling molecules in plants, highlighting their biosynthesis, perception, and degradation, particularly in stress and immune responses. It details classical nucleotide signals such as cytokinins and novel extracellular nucleotides like extracellular ATP (eATP) and NAD⁺ (eNAD⁺), describing their receptors, signaling pathways, and involvement in pathogen defense. The review also covers NAD⁺-derived signaling nucleotides produced by Toll/Interleukin-1 receptor–Resistance (TIR) domain enzymes, cyclic nucleotides including 2′,3′- and 3′,5′-cyclic nucleoside monophosphates, and “magic spot nucleotides” (MSNs) like guanosine tetraphosphate (ppGpp) in chloroplasts. While some nucleotide signals have well-characterized receptors and functions, others, such as certain cyclic nucleotides and deoxynucleosides, remain candidates requiring further research. The article underscores the complexity and versatility of nucleotide signaling in plants and the importance of understanding these pathways for advancing crop resilience and adaptation.