Light interacts with mechanical stress to regulate the seed-to-seedling transition.

The transition from seed to seedling represents a critical developmental phase that determines seedling survival, crop establishment, and yield potential. This intricate developmental process encompasses multiple stages: seed germination beneath the soil surface, the upward growth of etiolated seedlings through the soil environment to reach the soil surface, and subsequent greening to support photoautotrophic growth. The key environmental factors influencing the transition of buried seed to seedling establishment are light, mechanical resistance imposed by soil cover, and the intricate interplay between these factors. Recent studies have significantly enhanced our comprehension of the dynamic and complex nature of this transition: as a seedling pushes upward through the soil, light exposure steadily increases while mechanical resistance gradually decreases. In response, seedlings must orchestrate the initiation of light-regulated developmental processes with adjustments to mechanical stress. This review summarizes the molecular mechanism through which light and mechanical stress interact to facilitate and optimize the transition from seed to seedling in Arabidopsis, with a particular emphasis on deep sowing conditions in rice and maize. Insights into these molecular mechanisms can advance our understanding of the seed-to-seedling biology and contribute to the genetic improvement of crops.