Zaxinone, A Potential Plant Hormone: Biosynthesis, Signaling, and Applications

Zaxinone, a carotenoid-derived metabolite, has recently emerged as a promising regulator of plant growth, signaling, and resilience. Initially discovered in 2018 as a compound that influences plant–microbe interactions, particularly with arbuscular mycorrhizal (AM) fungi, zaxinone has expanded our understanding of plant hormones. Synthesized from carotenoids via carotenoid cleavage dioxygenases (CCDs), zaxinone plays an integral role in regulating various physiological processes, including root architecture, nutrient uptake, and response to stress. Its multifaceted nature positions it at the crossroads of hormone-like behavior and regulatory metabolites, interacting with established plant hormones such as auxins, strigolactones (SLs), and abscisic acid (ABA). Zaxinone modulates gene expression patterns, enhancing plant growth under optimal conditions and fostering stress resilience in adverse environments. Notably, its ability to influence nutrient acquisition, particularly phosphorus, and improve drought tolerance highlights its agricultural potential. This chapter explores the biosynthesis, signaling mechanisms, and physiological roles of zaxinone, examining its emerging applications in crop improvement, sustainable agriculture, and stress management. Despite its promising functions, key questions remain about its homeostasis, receptor interactions, and full range of biological effects, making zaxinone an exciting subject for future research in plant biology and agriculture.