Signal perception at the plasma membrane
The plant Symbiosis Receptor Kinase (SYMRK) is required at the early stages of symbiosis between plants and arbuscular mycorrhiza fungi, between actinorhiza hosts and Frankia bacteria and between legumes and rhizobia (Stracke et al., 2002; Markmann et al., 2008). SYMRK is essential for a plant cell reprogrammation that allows the entry of microsymbionts. SYMRK is a membrane bound receptor-like kinase (RLK) containing a signal peptide, an extracellular domain with three leucine rich repeat motifs, a transmembrane segment and a functional protein-kinase domain. We use several approaches to understand SYMRK mediated signalling. Tagged versions of SYMRK have been introduced into Lotus japonicus plants in order to study the spatiotemporal dynamics of SYMRK during the symbiotic response and the potential SYMRK interactome. An antibody raised against the extracellular domain of SYMRK shows excellent potential to study the native protein. To further unravel the mechanism of action of this RLK, the SYMRK interactome is under investigation. A yeast two-hybrid screening with the SYMRK kinase domain as bait led to the identification of four Ubiquitin E3-ligase proteins called SINA (Seven In Absentia). Several SYMRK interactors were isolated through a yeast split-ubiquitin screen. The interactors are tested in planta using the split YFP (BIFC) system. To investigate the role of the resulting interactors in symbiosis, RNAi constructs targeting the corresponding genes are introduced into Lotus japonicus by hairy root transformation or stable transformation and the symbiotic phenotypes are analysed after challenging with symbiotic inducers. The analysis of the SYMRK complex and SYMRK dynamics will provide insight into symbiotic signal transduction and plant receptor function.
Markmann, K., Giczey, G., and Parniske, M. (2008). Functional adaptation of a plant receptor-kinase paved the way for the evolution of intracellular root symbioses with bacteria. PLoS Biol. 6, e68.
Stracke, S., Kistner, C., Yoshida, S., Mulder, L., Sato, S., Kaneko, T., Tabata, S., Sandal, N., Stougaard, J., Szczyglowski, K., and Parniske, M. (2002). A plant receptor-like kinase required for both bacterial and fungal symbiosis. Nature 417, 959-962.