Thesis title: Generation of plants with high germination potential
Plants evolved several strategies to cope with the ever-changing environment. An 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 known, the ones permitting plants to germinate in the absence of light 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 levels of the pro-germination hormone Gibberellin (GA) prompts Cardamine seeds to germinate in both dark and light conditions. Via genetic and molecular biology experiments, we show that the expression levels of the Cardamine GA biosynthetic genes ChGA3OX1 and ChGA3OX2 stay high independently of light conditions. Our data support the proposal that Cardamine is a new model system suitable for light-independent germination studies. To investigate GA and ABA dynamics during seed germination, in both Arabidopsis and Cardamine, we took advantage of advanced biosensors. While waiting for Cardamine transgenic lines, our analysis on the Arabidopsis WT and dag1 mutant lines reveal that inactivation of AtDAG1 results in increased GA levels in mutant radicles and tissue-specific ABA reductions upon GA treatment and light exposure. These findings provide a detailed molecular map of hormone regulation during germination, highlighting the role of DAG1 in fine-tuning GA dynamics and the antagonistic GA-ABA relationship under various environmental conditions. Additionally, our research on light-independent germination mechanisms in Cardamine inspired us to explore practical applications of these insights. According to the SDG “zero hunger”, which aims to end all forms of hunger and malnutrition by 2030, we have assessed the germination and nutritional properties of Brassica species, focusing on the polyphenol content and ability to germinate efficiently in darkness. Our comparative analysis of these microgreens provided valuable insights into the evolutionary adaptations of plants to diverse environmental conditions, with potential applications in agriculture.
This work represents a significant step forward in resolving long-standing questions about plant germination mechanisms and provides a foundation for future studies in the field of plant developmental biology and agricultural science.