An emerging signaling hub: KAI2 at the nexus of phytohormone networks

The KARRIKIN INSENSITIVE 2 (KAI2) receptor, originally characterized for its role in seed germination and light-responsive development, is now recognized as an important signaling component with broad physiological relevance across plant species. While KAI2 is perhaps best known for perceiving exogenous smoked-derived karrikins, recent discoveries have revealed extensive crosstalk between KAI2-mediated signaling and multiple phytohormone pathways. We synthesize the current knowledge of KAI2 crosstalk with core plant hormones like strigolactones, auxin, ethylene, gibberellins, abscisic acid, cytokinins, and salicylic acid. We highlight shared signaling components, transcriptional regulation, and physiological outcomes. We examine how KAI2 signaling modulates hormone signaling and discuss the emerging view of KAI2 as an integrator of environmental and hormonal cues, particularly in stress adaptation and developmental plasticity. Finally, we propose new approaches, including proximity-labeling screens to dissect KAI2's full signaling potential and to explore open questions surrounding the identity and regulation of the endogenous putative KAI2 ligand. These insights position KAI2 as an evolving hub in the plant-signaling network, with implications for both fundamental research and crop improvement.