Light and hormone interactions in the seed-to-seedling transition

•The seed-to-seedling transition is a critical stage of plant development.•Light-dependent photoreceptor activation impacts the seed-to-seedling transition.•Hormone signaling adjusts the timing and success of the seed-to-seedling transition.•Light-hormone integration tunes the seed-to-seedling transition to external cues.•Seed-to-seedling transition regulation impacts short- and long-term plant dynamics.

Plants exhibit sensitivity to dynamic or changing environments and respond to such fluctuations through short- and long-term adaptive responses. The transition from seed to established seedling is a critical phase of the plant life cycle. This brief, but highly important, phase is linked to species persistence and impacts long-term population dynamics. During the seed-to-seedling transition, key factors that modulate plant form and function are light, hormones, and integrated signaling at the light-hormone interface. During this stage of early plant development, germination, seedling development and the critical heterotrophic-to-autotrophic conversion, the latter of which includes chloroplast development and differentiation, are modulated by external light parameters and homeostasis of several plant hormones. Specific mechanisms used to mediate responses to light and/or hormones during the seed-to-seedling transition include the regulation of gene expression, protein dynamics, and metabolites (including sugars and reactive oxygen species). In this review, we highlight key mechanistic factors and components that are especially linked to integrating responses to light and hormones during germination and the post-germinative seed-to-seedling transition. These light-/hormone-dependent mechanisms have implications for short- and long-term dynamics and diversity of natural plant species and communities.