Our model plant: The moss Physcomitrella patens
Physcomitrella patens is a member of the bryophytes (mosses) and is characterized by a number of specific features that placed it into the group of model plants. Its evolutionary position at the basis of land plants allows the study of the evolution of processes in plant biology. Furthermore, multiple molecular tools were developed that enable the analysis of different processes at the molecular level. Most importantly, the function of any gene can be analysed by targeted gene deletion (knockout mutants). This technique is based on the high frequency of homologous recombination also present in bacteria yeast or eukaryotic stem cells, but that does not occur in other land plants. Such analyses are further facilitated by the predominant haploid generation of the moss: the deletion of a single gene cannot be counterbalanced by a second allele and frequently results in a deviating phenotype. Despite the simple body plan, the P. patens genomes encodes for ~32.000 proteins thereby exceeding the gene number of human (~22.000) and of the model seed plant Arabidopsis thaliana (~27.000). The generation of transgenic P. patens lines takes a few weeks and the plants can be easily cultivated at different growth conditions for subsequent analyses.
Molecular mechanisms of abiotic stress adaptation
Plants are sessile organisms that cannot escape from adverse environmental conditions. Thus, to ensure survival of plants in nature they evolved specific mechanisms that confer stress adaptation. Since mosses were the first plants that colonised the land P. patens is particularly suited to study the essential mechanisms underlying the adaptation to different abiotic stresses. We investigate these mechanisms at the molecular level to uncover the genetic, biochemical and physiological processes that underlie the high degree of tolerance of P. patens to abiotic stress. We focus on the identification of genes that encode for proteins that have an essential role in the acquisition of stress tolerance. These proteins are members of particular stress-associated signaling pathways or exert their function in the maintenance of cellular homeostasis.
Biogenesis and function of non-coding RNAs
Protein encoding genes only account for a minor portion of the genome. However, almost the complete genome is transcribed into RNA suggesting that the vast majority of transcripts belong to different classes of non-coding RNA. We focus on biogenesis pathways of different classes of small non-coding RNAs (sRNAs) and their function in the control of gene expression. They act as important regulators of gene expression in many fundamental biological processes controlling the expression of their target genes at the post-transcriptional level by binding to reverse-complementary sequences within target RNAs directing RNA cleavage or the inhibition of translation (RNA interference, RNAi). Furthermore, sRNAs were shown to induce DNA modifications at cognate genomic regions causing an epigenetic control of gene expression. We analyse essential components of the RNAi machinery by the generation of targeted knockout lines of the corresponding genes. The molecular analysis of the small RNA pools and the effects on the regulation of their targets provide insights into the divergence of RNAi pathways in plants. Applying these approaches we already identified substantial differences to known RNAi pathways of seed plants. We are also interested in the evolution of different sRNA classes and their cognate regulatory networks. By comparing the miRNA repertoire and their cognate targets in land plants we aim at the identification of essential miRNA-dependent regulatory networks in plants. By this, we also want to understand the basic principles of this type of gene regulation. The knowledge of sRNA biogenesis and function further can be exploited for biotechnological applications.