The role of light in shaping plant growth: mechanisms of photomorphogenesis and hormonal integration during seedling development

Light is not merely an energy source for plants but a critical environmental signal that determines early developmental outcomes. The transition from seed germination to seedling establishment represents a sensitive and tightly regulated phase during which plants continuously interpret light cues to optimize growth, survival, and resource allocation. This transition involves a fundamental shift from skotomorphogenesis to photomorphogenesis and is governed by a highly dynamic and interconnected regulatory network. At the core of this network, photoreceptors perceive distinct light wavelengths and initiate signaling cascades that converge on key transcriptional regulators to reprogram gene expression. These light-driven pathways are extensively integrated with phytohormonal networks, where crosstalk among auxin, cytokinin, gibberallins (GA), abscisic acid (ABA), ethylene, brassinosteroids (BR), and jasmonic acid (JA) acts as a central driver of developmental decisions. Rather than acting independently, these hormonal pathways interact in a context-dependent manner to fine-tune processes such as seed germination, hypocotyl elongation, apical hook formation, cotyledon opening, chloroplast development, and root architecture. Emerging evidence highlights additional layers of control and new molecular players that further refine the spatial and temporal coordination of these responses, ensuring that early seedling development remains highly adaptable to fluctuating environmental conditions. This review synthesizes how light signaling coordinates with phytohormones and molecular mechanisms to execute the various developmental stages of a germinating seedling.