Sleeping but not defenseless: seed dormancy and protection.

To ensure their vital role in disseminating the species, dormant seeds have developed adaptive strategies to protect themselves against pathogens and predators. This is orchestrated through the synthesis of an array of constitutive defenses that are put in place in a developmentally regulated manner, which are the focus of this review. We summarize the defense activity and the nature of the molecules coming from the exudate of imbibing seeds that leak into its vicinity, also referred to as the spermosphere. As a second layer of protection, the dual role of the seed coat will be discussed; as a physical barrier and a multi-layered reservoir of defense compounds that are synthesized during seed development. Since imbibed dormant seeds can persist in the soil for extended times, we address the question if during this period, a constitutively regulated defense program is switched on to provide further protection, using the well-defined pathogenesis-related (PR) protein family. In addition, we review the hormonal and signaling pathways that might be involved in the interplay between dormancy and defense and point out questions that need further attention.