Plants have 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. While the molecular mechanisms underlying light-induced seed germination are well understood, those governing germination in the dark are still vague, mostly due to the lack of suitable model systems. Here, we employ Cardamine hirsuta, a close relative of Arabidopsis, as a powerful model system to uncover the molecular mechanisms underlying light-independent germination. By comparing Cardamine and Arabidopsis, we show that maintenance of the pro-germination hormone gibberellin (GA) levels prompt Cardamine seeds to germinate under both dark and light conditions. Using genetic and molecular biology experiments, we show that the Cardamine DOF transcriptional repressor DOF AFFECTING GERMINATION 1 (ChDAG1), homologous to the Arabidopsis transcription factor DAG1, is involved in this process functioning to mitigate GA levels by negatively regulating GA biosynthetic genes ChGA3OX1 and ChGA3OX2, independently of light conditions. We also demonstrate that this mechanism is likely conserved in other Brassicaceae species capable of germinating in dark conditions, such as Lepidium sativum and Camelina sativa. Our data support Cardamine as a new model system suitable for studying light-independent germination studies. Exploiting this system, we have also resolved a long-standing question about the mechanisms controlling light-independent germination in plants, opening new frontiers for future research.

• Keywords
• Cardamine hirsuta, DOF AFFECTING GERMINATION1, gibberellins, light, seed germination,
• MeSH
• Arabidopsis genetics   metabolism   MeSH
• Cardamine * genetics   metabolism   physiology   radiation effects   growth & development   MeSH
• Gibberellins * metabolism   MeSH
• Germination * radiation effects   genetics   physiology   MeSH
• Arabidopsis Proteins metabolism   genetics   MeSH
• Gene Expression Regulation, Plant MeSH
• Seeds * growth & development   genetics   radiation effects   metabolism   MeSH
• Light MeSH
• Transcription Factors metabolism   genetics   MeSH
• Feedback, Physiological MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Gibberellins * MeSH
• Arabidopsis Proteins MeSH
• Transcription Factors MeSH

Plants in habitats with unpredictable conditions often have diversified bet-hedging strategies that ensure fitness over a wider range of variable environmental factors. A striking example is the diaspore (seed and fruit) heteromorphism that evolved to maximize species survival in Aethionema arabicum (Brassicaceae) in which external and endogenous triggers allow the production of two distinct diaspores on the same plant. Using this dimorphic diaspore model, we identified contrasting molecular, biophysical, and ecophysiological mechanisms in the germination responses to different temperatures of the mucilaginous seeds (M+ seed morphs), the dispersed indehiscent fruits (IND fruit morphs), and the bare non-mucilaginous M- seeds obtained by pericarp (fruit coat) removal from IND fruits. Large-scale comparative transcriptome and hormone analyses of M+ seeds, IND fruits, and M- seeds provided comprehensive datasets for their distinct thermal responses. Morph-specific differences in co-expressed gene modules in seeds, as well as in seed and pericarp hormone contents, identified a role of the IND pericarp in imposing coat dormancy by generating hypoxia affecting abscisic acid (ABA) sensitivity. This involved expression of morph-specific transcription factors, hypoxia response, and cell wall remodeling genes, as well as altered ABA metabolism, transport, and signaling. Parental temperature affected ABA contents and ABA-related gene expression and altered IND pericarp biomechanical properties. Elucidating the molecular framework underlying the diaspore heteromorphism can provide insight into developmental responses to globally changing temperatures.

• MeSH
• Brassicaceae * genetics   physiology   metabolism   MeSH
• Germination * genetics   physiology   MeSH
• Abscisic Acid metabolism   MeSH
• Fruit * genetics   physiology   growth & development   metabolism   MeSH
• Gene Expression Regulation, Plant * MeSH
• Plant Growth Regulators metabolism   MeSH
• Seeds * genetics   physiology   growth & development   metabolism   MeSH
• Temperature * MeSH
• Transcriptome genetics   MeSH
• Plant Dormancy genetics   physiology   MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Abscisic Acid MeSH
• Plant Growth Regulators MeSH