Aethionema arabicum: a novel model to study light-regulated seed germination
Besides photosynthesis, light has an important role in plant development, including seed germination. Seeds are classified into three categories based on their response to white light during germination: (I) seeds that require light to germinate; (II) seeds that germinate with or without light, and (III) seeds whose germination is inhibited by light. The seeds of the widely used laboratory plant Arabidopsis thaliana belong to the first category; they need a minimum of light to germinate, and the molecular mechanism of light-induced germination was intensively studied. In contrast, we know very little about the light inhibition of germination. A remarkable natural variation observed in Aethionema arabicum (Brassicaceae), a relative of Arabidopsis, will allow filling this gap. Seeds of one accession originating from Turkey (TUR) are light-insensitive (category II), whereas seeds of another accession from Cyprus (CYP) do not germinate in the light (category III), although the two accessions are genetically very similar. Interestingly, the germination of CYP seeds is not just temporarily inhibited by the light: extended light exposure results in a “memory” effect that prevents germination for a long period even if seeds are transferred back to the favorable dark condition (secondary dormancy). We hypothesize, that the light inhibited germination is a day-length sensing mechanism to ensure the proper timing of germination in early spring.
In the frame of the NKFIH-FWF Joint Research Project, we would like to understand the photobiological aspects and the molecular mechanism of light-inhibited and light-insensitive germination. We also investigate the light-induced secondary seed dormancy and its occurrence in the Aethionemeae genus as an adaptation to the local environment.