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1. Joint effects of demography and natural selection on the molecular evolution of wild tomatoes: In collaboration with Dirk Metzler at the LMU-Munich, we seek to understand the population genetic history of wild tomatoes. We have developed evolutionary genetic models to account for the population substructure and speciation history of this group of closely related tomato species. These models have helped to define the appropriate null model against which to examine patterns of molecular evolution for a suite of candidate genes in stress response pathways. An ultimate goal is to determine the role of natural selection in shaping sequence and functional diversity for this and other gene classes in tomato and other species. This work has been funded by the DFG since 2008.

2. The interplay of pathogens, microRNAs, and regulation of resistance gene transcript abundance for rapid evolutionary responses in plants: We are currently investigating the co-evolution between the miR482 gene family and the resistance gene targets within the Solanaceae. Seven miR482 genes are expressed in wild tomatoes and are predicted to negatively regulate approximately 20% of the R-genes in tomato. During infection by Phytophthora infestans, we observe a down-regulation of these miR482 genes in tomato and could document a corresponding up-regulation of their predicted R-gene targets. Since most R-genes are predicted to be targeted by multiple miR482 paralogs, this may result in a degree of redundancy. To what degree the multiple layers of negative control have facilitated the rapid evolution of R-genes in wild plant species is the focus of a DFG funded project on rapid evolution.

3. Biocontrol of Phytophthora infestans on tomato: We are investigating the efficacy of biocontrol measures to restrict the plant pathogen, P. infestans, on tomato. We have identified bacterial and fungal species that limit the spread of P. infestans on plates and in planta. Furthermore we are investigating whether combination treatments are more effective than single isolate treatments. Ultimately we seek to identify the mechanistic basis of effective pathogen control.

4. Biodiversity of protists living in close association with Arabidopsis sp.: Like humans, plants live in close association with microbes. Some of these are pathogens or opportunists, whereas others are proven to be beneficial to their hosts. In collaboration with Prof. Michael Bonkowski at the University of Cologne, we are investigating the biodiversity of the underexplored lineages of protists living in close association with species of Brassicaceae. To this end, metabarcoding methods for major groups of protists have been tested and improved in our labs. We are currently analyzing how the community composition of oomycetes and protists is differentiated across different plant tissues and the soil substrate. The ultimate goal is to discover novel microbes that are beneficial to their hosts and provide new insights that can be translated into effective crop protection. This work has been supported by Ceplas, the Cluster of Excellence on Plant Science (EXC 1028) since 2012.

5. Evolution of symbiosis genes in Lotus species: In a collaboration with Martin Parniske at the LMU-Munich we are studying a suite of symbiosis genes in European and Asian species of Lotus. In this project, we combine population genetic studies, phylogenetic studies and functional work to determine the types of selection that have operated on these loci and to understand how natural variation at particular candidate loci affects the interspecific interaction between host and symbiont. This work has been funded by the DFG since 2008.

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