Specific projects:

RHO-like GTPase function in resistance and susceptibility to plant diseases

RHO-like GTPases of plants (RAC/ROPs) are signal transduction components involved in processing of extracellular signals in eukarytotic cells. We are interested in signalling cascades that support pathogenic entry into barley epidermal cells and might be targets of fungal virulence strategies. Starting from reverse genetic approaches and yeast two hybrid screening, we identified barley and Arabidopsis RAC/ROPs and RAC/ROP interacting proteins involved in susceptibility and resistance to powdery mildew (Hoefle et al. 2011; Schultheiss et al. 2008; Schultheiss et al. 2002). By in-planta imaging of RAC/ROP-related protein dynamics and protein-protein interaction, we display signal transduction at the authentic plant-microbe interface. This led to identification of the host cytoskeleton as a target of fungal virulence strategies. Additional plant developmental and physiological studies revealed that barley RAC/ROPs have important functions in cell polarity, epidermal cell development and abiotic stress responses. The highly conserved and essential nature of plant RAC/ROP proteins might have made them ideal targets for fungal virulence strategies (Hoefle et al. 2011; Scheler et al. 2016).

Currently we focus the mechanistic basis of RAC/ROP mediated susceptibility to powdery mildew by analysing ROP regulation and several RAC/ROP-interacting proteins, which have impact on the plant cytoskeleton, gene expression and membrane dynamics (Huesmann et al. 2012; Hoefle et al. 2011; Opalski KS et al. 2005; Reiner et al. 2016; Schnepf et al. 2018). These processes are key to accommodation of fungal infection structures in intact plant cells and may provide a target for plant breeding and biotechnology for disease resistance.

Green GFP-RACB contrasted by soluble DsRED. Confocal laser scanning microscopy.
Barley cell surface ROP signaling in susceptibility to parasitic fungal cell entry. The barley ROP protein HvRACB might be activated from the cell surface and supports fungal entry into barley epidermal cells with support from RIC and RIP scaffold proteins. The fungal effector ROPIP1 can directly bind RACB and support host cell entry. RACB activity and abundance are further controlled via MAGAP1 and RBK1, respectively. Postulated components are bordered with dashed lines. Dashed arrows show indirect, postulated or speculative interactions.Engelhardt et al. (2020) Cells 9: 2016