Origins of the seed: The "golden-trio hypothesis"

The seed is an evolutionary innovation in the plant kingdom. While human civilization depends heavily on seed production, how the seed trait emerged remains elusive. In this opinion article, a "golden-trio hypothesis" is proposed based on our investigations of LEC1 gene functions in Adiantum capillus-veneris. This hypothesis posits that a "seed program" arose from spatiotemporal integration of three key components: assimilate flow, ABA-mediated stress responses, and stress-induced LEC1 expression. Thus, the evolutionary innovation of seeds should be considered not a simple event resulting from new genes; rather, it represents the outcome of a series of physiological and morphological innovations that emerged prior to and regardless of the origin of the seed program. This new perspective could help us tackle some long-standing questions around the puzzling origin of seeds.