Emerging Paradigms in Strigolactone Biosynthesis, Signaling, and Evolutionary Dynamics

Originally identified as root-derived exudates that trigger the germination of parasitic weed seeds, strigolactones (SLs) were later discovered to be crucial facilitators of plant symbiotic associations with arbuscular mycorrhizal fungi and then found to be a bona fide plant hormone class in 2008. Thereafter, SLs have been revealed as versatile regulators of plant development, regulating processes as diverse as shoot branching, root architecture, leaf senescence, vasculature formation, and stem secondary growth. Beyond these developmental roles, they function as signaling molecules, enabling plants to adapt to and withstand environmental stresses. This review focuses on the evolutionary diversification of SL biosynthesis and perception, emphasizing how pathway specialization, receptor remodeling, hydrolysis, and downstream signaling generate distinct endogenous and interorganismal functions. It details the complex biosynthetic pathway of SLs, highlighting key enzymes that work together to convert carotenoid precursors into the diverse SLs. The review then explores SL signaling mechanisms, emphasizing the receptor DWARF14 and its interactions with downstream components, such as DWARF53 proteins, which influence how plants perceive and respond to SLs. It also examines the evolutionary aspects of SL biosynthesis and signaling, especially their dual roles in promoting plant-microbe symbiosis and regulating hormone activity. This comprehensive update enhances our understanding of SL functions at the molecular and ecological levels. Moreover, the review discusses the relationship between SLs and karrikins, focusing on DWARF14 and the KARRIKIN INSENSITIVE 2 receptor, and explores potential applications of SLs in agriculture to improve crop resilience and yields. This in-depth account of how SLs operate as master regulators in plant life provides insights into both their evolutionary significance and their potential utility in agriculture.