Molecular Mechanisms of Hormonal Regulation of Plant Immunity

The phytohormones salicylic acid (SA), jasmonic acid (JA), and ethylene (ET) play a central role in the regulation of plant immune responses. This review summarizes current knowledge on the molecular mechanisms underlying the biosynthesis, perception, and transcriptional, and post-translational regulation of SA, JA, and ET signaling cascades. The complex networks of interactions between these pathways are examined in detail, extending beyond the classical paradigm of SA–JA/ET antagonism. It has been shown that the nature of the interaction (antagonism or synergism) depends on a number of factors, including the type of pathogen, the plant species, and the spatiotemporal organization of the signal. Special attention is given to recently uncovered details, including the refinement of the steps in the phenylpropanoid pathway for SA biosynthesis, the functional divergence of NPR1/2 and COI1/2 homologs across different plant species, and novel regulatory mechanisms. The studies presented provide a deeper understanding of how hormonal signals interact during the establishment of plant defense responses and may serve as a foundation for developing new strategies to enhance crop resistance to biotic stresses.