Phytohormones in fungi: inter-kingdom modulators or fungal self-controlling elements?

SUMMARYLeveraging data from innovative experimental approaches, omics technologies, and bioinformatics, we offer new insights into how fungi communicate with and perceive their environment to achieve ecological success. By integrating comparative data from both the fungal and plant kingdoms, we critically reassessed the evolutionary, biochemical, and functional landscape of phytohormones in fungi, challenging the conventional notion that these molecules serve exclusively as plant regulators or as means of communication with them. Our analysis demonstrates that fungi not only synthesize a diverse array of phytohormones-including auxins, cytokinins, gibberellins, abscisic acid, ethylene, brassinosteroids, salicylic acid, and oxylipins-but also possess hormone-sensing and signal transduction mechanisms architecturally distinct from those of plants. Employing genomics, phylogenetics, and structural analyses, the review uncovers that many hormone biosynthetic and sensing pathways in fungi are evolutionarily ancient, sometimes predating their roles in plant-fungus interactions, and that some pathways show convergence rather than direct gene homology. Fungal phytohormones regulate development, growth, and metabolism, thereby playing key functions in their ecological context. The review emphasizes that, while biosynthetic pathways tend to be highly conserved, perception and signaling mechanisms in fungi are more varied and often remain poorly understood. We conclude that fungi have an intrinsic and autonomous hormonal physiology that underpins their ecological adaptability and success. Collectively, this analysis reframes fungal biology, highlighting the need for deeper investigation into the signaling and regulatory roles of phytohormones in fungi beyond their interactions with plants.