The Lipka lab

Research in our lab is focused on the molecular dissection of Arabidopsis
nonhost resistance and compatibility to fungal pathogens.

Plants are constantly exposed to a plethora of potential pathogens with different infection strategies and lifestyles. Nevertheless, disease represents the exception in natural plant communities. The reason is that most plants are immune to the majority of would-be pathogens and susceptible to only a relatively small number of adapted microbes. The phenomenon that an entire plant species is resistant to all genetic variants of a non-adapted pathogen species is termed nonhost resistance (NHR) and defines the most robust form of plant immunity (reviewed in Lipka et al., 2008). Thus, NHR delimits the host range of phytopathogenic microorganisms and impinges on pathogen radiation and speciation.
Due to its complex nature, NHR has previously not been studied in detail. Recently, the establishment of model interaction systems utilizing Arabidopsis and non-adapted powdery mildew fungi allowed the identification of several key components and conceptual conclusions (Lipka et al., 2008).
It is generally accepted that inducible components of NHR and basal resistance (which defines the plant’s ability to reduce the severity of disease caused by adapted pathogens) both involve recognition of slowly evolving microbial- or pathogen-associated molecular patterns (MAMPS or PAMPs) by transmembrane pattern recognition receptors (PRRs) (reviewed in Schwessinger and Zipfel, 2008). We and others recently identified a LysM-domain receptor-like kinase, CERK1, which is required for perception of the fungal PAMP chitin and resistance to fungal pathogens (Miya et al., 2007; Wan et al., 2008), but also for basal resistance to bacterial pathogens (Gimenez-Ibanez et al., 2009). Structure-function and ligand-binding analyses are currently conducted to characterize CERK1 function in more detail.

MAMP-mediated recognition ultimately leads to activation of executive defense mechanisms. We recently used forward genetics to identify molecular components that are required for entry control of non-adapted fungal pathogens into epidermal leaf tissue. This approach allowed the identification of three molecular components of Arabidopsis nonhost resistance, PENETRATION (PEN) 1, 2 and 3 (Collins et al., 2003; Lipka et al., 2005; Stein et al., 2006). The plasma membrane resident Qa-SNARE PEN1 and ABC transporter PEN3, and the peroxisome associated glycosyl hydrolase PEN2 are all subject to pathogen-induced cell polarization. Mechanistically they are involved in focal vesicle transport processes and the local activation and release of small secondary metabolites at sites of attempted fungal invasion (Collins et al., 2003; Lipka et al., 2005; Stein et al., 2006; Kwon et al., 2008; Lipka et al., 2008; Bednarek et al., 2009). We currently characterize PEN protein-mediated defense mechanisms by a combination of cell & molecular biological, genetic and biochemical approaches.
Post-invasion resistance to non-adapted biotrophic fungal pathogens is associated with the execution of a local cell death response, which is restricted to epidermal cells under pathogen attack and controlled by the lipase-like proteins EDS1, PAD4 and SAG101 (Lipka et al., 2005). Systematic gene interaction analyses provided evidence for functionally redundant but operationally distinct pre- and post-invasive immune responses, which collectively explain the durable and robust nature of nonhost resistance (Lipka et al., 2005; Lipka et al., 2008).

The abilities to overcome NHR, to colonize a plant species and to reproduce represent the basic requirements for pathogen host plant adaptation and establishment of basal compatibility (reviewed in O’Connell & Panstruga, 2006). It is conceivable that adapted pathogens must have evolved mechanisms to evade or suppress the plant’s basal defense machinery and to manipulate plant cell functions for their own benefit. They do so by utilizing a repertoire of effector molecules which target a variety of distinct plant mechanisms (reviewed in Speth et al., 2007).
We are working with a collection of powdery mildew species for which Arabidopsis either represents a host or a nonhost plant. Our objective is to analyze the secretome of in planta infection structures in order to identify and characterize the function of effector proteins. In addition to genomic sequence information we currently analyze fungal cDNA libraries generated from infected Arabidopsis plants. Secreted proteins are being identified using computational signal peptide prediction. Functional classification of candidate proteins on the basis of homology searches (if applicable) and protein motif detection will be complemented by experimental functional characterization. This will include delivery of candidate effectors into Arabidopsis cells to evaluate their ability to trigger or suppress plant defense responses. In particular, we are interested to identify secreted fungal effector molecules that impinge on the membrane compartment-associated defense machineries described above.

Collaborators


Ten Feizi, Imperial College London, UK


Sophien Kamoun, Sainsbury Lab, Norwich, UK


Eric Kemen, Sainsbury Lab, Norwich, UK


Marcus Koch, University of Heidelberg, Germany


Richard O’Connell, MPIZ Cologne, Germany


Martin Parniske, LMU Munich, Germany


Paul Schulze-Lefert, MPIZ Cologne, Germany


Shauna Somerville, Stanford University, USA


Richard Strasser, BOKU Vienna, Austria

References:

Bednarek, P., Pislewska-Bednarek, M., Svatos, A., Schneider, B., Doubsky, J., Mansurova, M., Humphry, M., Consonni, C., Panstruga, R., Sanchez-Vallet, A., Molina, A., and Schulze-Lefert, P., 2009. A glucosinolate metabolism pathway in living plant cells mediates broad-spectrum antifungal defense. Science 323, 101–106.

Collins, N.C., Thordal-Christensen, H., Lipka, V., Bau, S., Kombrink, E., Qiu, J.L., Hueckelhoven, R., Stein, M., Freialdenhoven, A., Somerville, S.C., Schulze-Lefert, P., 2003.: SNARE-protein-mediated disease resistance at the plant cell wall. Nature, 425, 973-977.

Gimenez-Ibanez, S., Hann, D.R., Ntoukakis, V., Petutschnig, E., Lipka, V., Rathjen, J.P., 2009. AvrPtoB targets the LysM receptor kinase CERK1 to promote bacterial virulence on plants, Current Biology 19, 423-429.

Kwon, C., Neu, C., Pajonk, S., Yun, H.S., Lipka, U., Humphry, M., Bau, S., Straus, M., Kwaaitaal, M., Rampelt, H., Kasmi, F., Juergens, G., Parker, J., Panstruga, R., Lipka, V., Schulze-Lefert, P., 2008a. Co-option of a default secretory pathway for plant immune responses. Nature, 451, 835-840.

Lipka, U., Fuchs, R., Lipka, V. (2008) Arabidopsis non-host resistance to powdery mildews, Current Opinion in Plant Biology 11: 404-411

Lipka, V., Dittgen, J., Bednarek, P., Bhat, R., Wiermer, M., Stein, M., Landtag, J., Brandt, W., Rosahl, S., Scheel, D., Llorente, F., Molina, A., Parker, J., Sommerville, S., Schulze-Lefert, P., 2005. Pre- and postinvasion defences both contribute to nonhost resistance in Arabidopsis. Science, 310, 1180-1183.

Miya, A., Albert, P., Shiny, T., Desaki, Y., Ichimura, K., Shirasu, K., Narusaka, Y., Kawakami, N., Kaku, H., Shibuya, N., 2007. CERK1, a LysM receptor kinase, is essential for chitin elicitor signaling in Arabidopsis. Proc Natl Acad Sci U S A 104, 19613–19618.

O´Connell, R.J., Panstruga, R., 2006. Téte-a-téte inside a plant cell: Establishing compatibility between plants and biotrophic fungi and oomycetes. New Phytol., 171, 699-718.

Schwessinger, B., Zipfel, C., 2008. Curr. Opin. Plant Biol., 11, 389-395.

Speth, E.B., Lee, Y.N., He, S.Y., 2007. Pathogen virulence factors as molecular probes of basic plant cellular functions. Curr. Opin. Plant Biol., 10, 580-586.

Stein, M., Dittgen, J., Sanchez-Rodriguez, C., Hou, B.H., Molina, A., Schulze-Lefert, P., Lipka, V., Somerville, S., 2006. Arabidopsis PEN3/PDR8, an ATP cassette transporter, contributes to nonhost resistance to inappropriate pathogens that enter by direct penetration. Plant Cell, 18, 1-16.

Wan, J., Zhang, X.C., Neece, D., Ramonell, K.M., Clough, S., Kim, S.Y., Stacey, M.G., Stacey, G. 2008. A LysM receptor-like kinase plays a critical role in chitin signaling and fungal resistance in Arabidopsis. Plant Cell 20: 471–481.: