Research group Group Pawlowski
Our research is focussed on actinorhizal nitrogen-fixing root nodule symbiosis, a topic relevant for the understanding of root nodule symbioses in general as well as for the role of actinorhizal plants in soil restoration, shelter belts and erosion control.
In the context of actinorhizal symbioses, we focus on different questions:
1. All root nodule symbioses, rhizobia/legume and actinorhizal symbioses – which are entered by plants of the Fabales, Fagales, Rosales and Cucurbitales – go back to a common ancestor, which according to the newest phylogenomic analyses had evolved a complete symbiosis. Since the oxygen protection system for nitrogenase, required in symbioses with rhizobia as microsymbionts, is polyphyletic, the ancestral microsymbiont should have been a Frankia strain. This suggests that the earliest diverging Frankia clade (“cluster-2”) is closest to the ancestral microsymbiont. We analyse the symbioses of this clade regarding nutrient and signal exchange with the aim to use our results to transfer the symbiotic capability to a non-symbiotic, agriculturally relevant relative of hosts of cluster-2, namely, a cucurbit.
2. We also analyse the evolution of specific features in the actinorhizal microsymbiont Frankia in order to understand the differences between the symbioses of cluster-2 and the later diverging symbiotic clades.
3. The actinorhizal species with the greatest ecological relevance are members of the Casuarinaceae, in particular members of the genera Casuarina and Allocasuarina. Based on the genome sequences of Frankia strains isolated from their nodules, their microsymbionts seem to have low diversity, and their stress tolerance ex planta – which can be high – does not reflect their stress tolerance in planta. Given that there are several cases where strains ostensibly isolated from actinorhizal nodules were actually living on the nodule surface, this asks for a re-evaluation. We are following an approach of direct sequencing of nodule DNA to analyse the in planta diversity of the microsymbionts, with the aim of improving inocula for (Allo-)Casuarina.
Group members
Group managers
Katharina Pawlowski
Professor
Members
Nadia Binte Obaid
PhD student
Marios Kontogiannis
MSc student
