Principal investigator:

Weigel, Detlef, Prof. Dr. Dr. h. c.,

Max-Planck-Institut für Entwicklungsbiologie

Abt. Molekularbiologie

Spemannstraße 35

72076 Tübingen

Phone: 49 7071 601 1411

E-mail: weigelspam prevention@tue.mpg.de

Summary:

Plants employ sophisticated mechanisms to recognize pathogen molecules and mount immune responses. Sometimes, however, plants mistakenly identify their own molecules as foreign and induce autoimmunity. Because pathogen detection is uncoupled from downstream signalling events, genetically conditioned autoimmunity offers unique inroads into understanding the plant immune system. A particularly interesting example is autoimmunity triggered by interactions between the A. thaliana RPW8 and RPP7 loci. In this case, specific pairs of alleles from different wild strains interact in F₁ hybrids to cause autoimmunity. The complex RPP7 locus encodes several NLR immune receptors, and several of these confer resistance against oomycetes. Although NLR receptors as a class were discovered over two decades ago, we still have only limited knowledge of how they are activated and what their direct signalling partners are. Similar to NLR loci, the RPW8 locus is also complex, with ample copy number and sequence variation between wild strains. The biochemical function of the RPW8 atypical resistance proteins, some of which confer resistance against fungi, is unclear, but they appear to function at the extrahaustorial membrane that encases haustoria, the structures formed at the interface of plant and invading oomycete or fungal hyphae. Our preliminary data suggest that RPW8 and RPP7 proteins can directly interact with each other, but that interaction is not sufficient for autoimmunity. Our aims in this project are: (1) Compare signalling specificity of RPW8 and RPP7, by studying how mutations known to alter either RPP7- or RPW8-dependent disease resistance affect RPW8/RPP7-triggered autoimmunity, and determining whether there is evidence for RPW8-RPP7 interaction during pathogen-induced immunity. (2) Elucidate subcellular specificity of RPW8-RPP7 interaction, by studying the subcellular localisation of both proteins, the requirement of trafficking components for RPW8/RPP7-triggered autoimmunity, and testing mutations predicted to alter localisation or activity of the two proteins. (3) Elucidate structural specificity of RPW8-RPP7 interaction, by identifying sequences that functionally distinguish autoimmune risk and non-risk alleles, by dissecting the RPW8 coiled-coil domains, and by determining the size and composition of protein complexes in which RPW8 and RPP7 proteins reside. The proposed work will reveal commonalities with or differences to other NLR signalling complexes, and form the basis for understanding the interaction of RPP7 and RPW8 proteins not only in the special autoimmunity situation, but also in regular plant immunity.