The plasma membrane (PM) represents a boundary of plants to sense changes in their biotic and abiotic environment. The PM is therefore the place of plants to recognise stress or potentially harmful conditions. Plant colonising microbes are recognised by pattern recognition receptors (PRRs) at the PM. These PRRs perceive, in a highly specific manner, microbial molecules such as bacterial flagellin or fungal chitin, which are defined as microbe-associated molecular patterns (MAMPs). Upon recognition, PRRs apparently share various signalling pathways to trigger plant immune responses resulting in biotic stress adaptation (Fig. 3). Research in my lab revealed that plants do not necessarily distinguish between microbial life styles and besides pathogens, beneficial microbes depend on immunosuppressive strategies to colonise plants. In deed, we observed a broad immunosuppressive activity exerted by the mutualist Piriformospora indica to colonise plant roots. Our aim is to understand the strategies applied by the fungus to manipulate immune signalling and whether these strategies differ from respective pathogenic activities.
By studying the mutualistic interaction of plants with Piriformospora indica, we identified Tubby-like proteins (TLPs) as being responsive to oxidative stress (e.g. H2O2, salt, drought stress) in plants. TLPs are conserved in eukaryotes and their dysfunction causes neurodegenrative diseases and obesity in mammals. In mammals, some Tubby (founding member of the TLP family) and TLPs are considered as PM-tethered transcription factors that are released under certain physiological adverse conditions by phospholipase C (PLC) to enter the nucleus. In plants, this PLC-driven PM dislodgement of TLPs is conserved and occurs upon oxidative stress (Fig. 3). However, in contrast to mammals, certain plant TLPs translocate to plastids (and possibly the nucleus). We currently aim at understanding the site and consequence of TLP action in/at plastids and whether TLPs are part of a receptor complex involved in oxidative stress perception and abiotic stress adaptation.
Our studies indicate commonalities and pecularities of stress adaptation on a tissue level. It is our clear focus to understand tissue-specificity (e.g. leaf vs. root) of pathways directing and conducting abiotic and biotic stress adaptation and to use this knowledge in sustainably improve crop productivity.
Figure 3 Simplistic view of abiotic and biotic stress signalling in plants mediated by Tubby-like proteins (TLPs) and pattern recognition receptors upon oxidative stress and microbial attack, respectively. TLPs may act as part of a plasma membrane-localised receptor complex (RC) and apparently translocate to yet to be identified plastid sites. MAPK, Map kinase; PLC, phospholipase C (see text for more details).
Reitz, M.U., Bissue, J.K., Zocher, K., Attard, A., Hückelhoven, R., Becker, K., Imani, J., Eichmann, R., Schäfer, P. (2012) The subcellular localization of Tubby-like proteins and participation in stress signaling and root colonization by the mutualist Piriformospora indica. Plant Physiology, 160, 349-64
Jacobs, S., Zechmann, B., Molitor, A., Trujillo, M., Petutschnig, E., Lipka, V., Kogel, K.H., Schäfer, P. (2011) Broad spectrum suppression of innate immunity is required for colonization of Arabidopsis roots by the beneficial fungus Piriformospora indica. Plant Physiology, 156, 726 - 740