On the origin of the seed habit
The ultimate goal of our project is to better understand the proximate mechanisms that brought about seeds during evolution. During the course of this work we want to clarify the molecular mechanisms, especially innovations in gene regulatory networks (GRN), that were involved in the origin of ovules and seeds. We will pursue our goal by studying the molecular developmental genetics of reproduction in the emerging model system Ceratopteris richardii. As a fern, C. richardii is a member of the monilophytes, which represent the closest living relatives of extant seed plants. Seed plants are comprised of angiosperms (flowering plants) and gymnosperms. We will pursue our goal in two independent ways, a ‘targeted candidate gene approach’, and an ‘unbiased transcriptomic approach’. In the candidate gene approach we will first reconstruct improved phylogenies of MIKCC-type MADS-box genes of land plants. This way we will identify the genes in ferns which are the closest relatives to the genes that control ovule and seed development in seed plants. In parallel, we will establish genome editing in C. richardii employing CRISPR-Cas9. Using this method we will knockout the closest relatives of floral organ and seed identity genes, as identified using the phylogeny reconstructions, in C. richardii. The mutant phenotypes of the knockout plants will provide insights into the function of these genes in ferns and their potential role during the origin of the seed. In the transcriptomics approach we will first provide transcriptome data of several informative developmental stages of the C. richardii sporophyte. We will compare this data with those of diverse seed plants, including gymnosperms such as Norway spruce (Picea abies) and flowering plants such as Arabidopsis, tomato and rice. To better distinguish ancestral from derived character states, we will also include suitable transcriptomes of the bryophyte models Marchantia polymorpha and Physcomitrium patens into our comparisons. The data obtained by us and several other members of the research unit ICIPS will be used to develop models of gene regulatory networks that will enable us to identify critical changes in regulatory genes during the origin of the seed in evolution.