A DOF transcriptional repressor-gibberellin feedback loop plays a crucial role in modulating light-independent seed germination.

Abstract

Plants evolved several strategies to cope with the ever-changing environment. One example of this is given by seed germination, which must occur when environmental conditions are suitable for plant life. In the model system Arabidopsis thaliana seed germination is induced by light; however in nature, seeds of several plant species can germinate regardless of this stimulus. Whereas the molecular mechanisms triggered by light for seed germination are well understood, the ones permitting plants to germinate in the dark are still vague mostly due to the lack of suitable model systems. Here we employ Cardamine hirsuta, a close Arabidopsis relative, as a powerful model system to uncover the molecular mechanisms underlying light-independent germination. Comparing Cardamine and Arabidopsis we show that the maintenance of the pro-germination hormone Gibberellin (GA) levels prompt Cardamine seeds to germinate in dark and light conditions. Via genetic and molecular biology experiments, we show that the Cardamine DOF transcriptional repressor DOF AFFECTING GERMINATION 1 (ChDAG1), homologous to the Arabidopsis DAG1 transcription factor, is involved in this process functioning to mitigate GA levels via negative regulation of ChGA3OX1 and ChGA3OX2 gibberellin biosynthetic genes, independently of light conditions. We also demonstrate that this mechanism is likely to be conserved in other Brassica species capable of germinating in dark conditions, such as Lepidium sativum and Camelina sativa. Our data support the proposal that Cardamine is a new model system suitable for light-independent germination studies. Exploiting this system we also resolved a long-time question about the mechanisms controlling the light-independent germination in plants, opening new frontiers for future studies.