SFB796 - Sub project C7


Modulation of cellular processes and Rac/Rop (Rho) activity in Arabidopsis by Pto TTSS effector proteins


Project summary

Plants effectively repel most attacking microbial pathogens based on an elaborate double-layered immune system. They are able to perceive conserved pathogen surface epitopes, and to trigger signaling cascades in response, which induce complex changes in cellular structures and processes that enable targeted cells to fend off attackers. Pathogen induced signaling cascades and cellular changes in plant cells have generally been characterized only to a limited extent. In particular the cell biology of plant interactions with bacterial pathogens is not well understood.

Successful pathogens transfer effector proteins into plant cells, which enable infection by shutting down defense reactions and/or by manipulating host cells to promote pathogen propagation. Many bacterial pathogens use a type three secretion system (TTSS) to directly inject effector proteins into the host cell cytoplasm. Single TTSS pathogens typically employ large sets of diverse effector proteins, which collectively are essential for infection, but individually tend to have subtle functions. In part because of this, the molecular and cellular functions of most effector proteins have not been well characterized.

Rac/Rop GTPases, the plant representatives of the ubiquitous eukaryotic Rho family of small GTPases, appear to play important roles in the control of structural changes and other processes in attacked plant cells, which are induced by plants to defend themselves or by pathogens to promote infection. However, these roles have only begun to be investigated and virtually nothing is known about Rac/Rop GTPase functions in interactions between dicotyledonous plants such as Arabidopsis and bacterial pathogens. Interestingly, many TTSS effectors of mammalian bacterial pathogens act by directly targeting the activity of host cell Rho GTPases. TTSS effectors of plant bacterial pathogens with similar functions remain to be identified.

Here, we propose to enhance our understanding of cellular and molecular processes enabling plant infection by important bacterial pathogens through the detailed cell biological characterization of well-established model interactions between two fully genetically tractable organisms. More specifically, we plan to determine functions of Pseudomonas syringae pv. tomato (Pto) TTSS effector proteins in the modulation of structures, processes and Rac/Rop GTPase activity in infected Arabidopsis cells. An important aim of this project is the identification of Pto TTSS effector proteins that directly target the activity of the Rac/Rop GTPases AtROP6 or AtROP10, which we have found to modulate Pto growth rates in infected Arabidopsis leaves.


Project relevant publications

Sun J, Eklund DM, Montes-Rodriguez A, Kost B.   (2015).   In vivo Rac/Rop localization as well as interaction with RhoGAP and RhoGDI in tobacco pollen tubes: analysis by low-level expression of fluorescent fusion proteins and bimolecular fluorescence complementation.   Plant J. 84: 83-98.

Stephan O, Cottier S, Fahlen S, Montes-Rodriguez A, Sun J, Eklund DM, Klahre U, Kost B.   (2014).   RISAP is a TGN-associated RAC5 effector regulating membrane traffic during polar cell growth in tobacco.   Plant Cell. 26: 4426-4447.

Potocky M, Pleskot R, Pejchar P, Vitale N, Kost B and Zarsky V.   (2014).   Live-cell imaging of phosphatidic acid dynamics in pollen tubes visualized by Spo20p-derived biosensor.   New Phytol. 203: 483-494.

Potocky M, Pejchar P, Gutkowska M, José Jiménez Quesada M, Potocka M, de Dios Alché Ramírez J, Kost B and Zarsky V.   (2012).   NADPH oxidase activity in pollen tubes is affected by calcium ions, signaling phospholipids and Rac/Rop GTPases.   J. Plant Physiol. 169: 1654-1663.

Richter S, Muller LM, Stierhof Y-D, Mayer U, Takada N, Kost B, Vieten A, Geldner N, Koncz C and Jurgens G.   (2012).   Polarized cell growth in Arabidopsis requires endosomal recycling mediated by GBF1-related ARF exchange factors.   Nature Cell Biol. 14: 80-86.

Kost B.   (2010).   Regulatory and cellular functions of plant RhoGAPs and RhoGDIs.   In: Integrated G Proteins Signaling in Plants ;   eds: S. Yalovsk, F. Baluska and A. Jones.   Springer Verlag, Heidelberg, Germany, p 27.

Yalovsky S, Bloch D, Sorek N and Kost B.   (2008).   Regulation of membrane trafficking, cytoskeleton dynamics and cell polarity by Rop/Rac GTPases.   Plant Physiol 147: 1527.

Kost B.   (2008).   Polarization of Rho (Rac/Rop) signaling in tip-growing plant cells.   Trends Cell Biol 18: 119.

Helling D, Possart A, Cottier A, Klahre U and Kost B.   (2006).   Tobacco pollen tube tip growth depends on plasma membrane polarization mediated by Nt PLC3 activity and endocytic membrane recycling.   Plant Cell 18: 3519.

Klahre U and Kost B.   (2006).   NtRhoGAP1 spatially restricts signalling of RAC/Rop to the apex of tobacco pollen tubes.   Plant Cell 18: 3033.

Klahre U, Becker C, Schmitt AC and Kost B.   (2006).   Interaction with Nt-RhoGDI2 is essential for normal Nt-Rac5 localization and activation in tobacco pollen tubes.   Plant J 46: 1018.

Kost B, Lemichez E, Spielhofer P, Tolias K, Carpenter C and Chua NH.   (1999).   Rac homologs and compartmentalized phosphatidylinositol 4, 5-bisphosphate act in a common pathway to regulate polar pollen tube growth.   J Cell Bio 145: 317.

Kost B, Spielhofer P and Chua NH.   (1998).   A GFP-mouse talin fusion protein labels plant actin filaments in vivo and visualizes the actin cytoskeleton in pollen tubes.   Plant J 16: 393.