The Receptor team studies how plants recognise and respond to invading plant pathogens.
Our work aims to unravel how plants resist pathogens by activating their immune response upon pathogen detection mediated by the cell-surface receptors of the plant and, conversely, how pathogens successfully elude resistance. We primarily focus on Solanaceous plants, as these represent economically important crop plants, such as tomato and potato.
Plant immune receptors
Plant immune receptors are also known as disease resistance (R) proteins. Immune receptors present at the cell surface are either receptor-like kinases (RLKs) or receptor-like proteins (RLPs), of which the latter lack a cytoplasmic kinase domain. The Cf resistance proteins of tomato are RLPs that mediate recognition of secreted effectors of the pathogenic extracellular fungus Cladosporium fulvum. These receptors initiate immune signalling, which eventually culminates in the hypersensitive response (HR). This HR is a form of programmed cell death that can contribute to the actual resistance response, but probably earlier immune responses, such as a very fast production of reactive active oxygen species (ROS), are more important for mounting resistance against the fungus. The HR is activated through a signal transduction pathway of which several signalling partners are currently known, such as the Cf co-receptors SOBIR1 and BAK1, and downstream MAP kinases. We also know that various phosphorylation events take place between the different signalling partners and that so-called cytoplasmic receptor-like cytoplasmic kinases (RLCKs) also play important roles in downstream immune signalling. However, we do not know how the various signalling steps are connected, what additional proteins do play a role in this and what the exact role is of the various RLCKs in immune signalling.
To gain more insight into the mechanisms behind the activation of plant immunity and its evasion by pathogens, we focus on the interaction between tomato and its strictly extracellular, biotrophic pathogen Cladosporium fulvum. This fungus is the causal agent of tomato leaf mould disease, a currently re-emerging disease that causes yield losses worldwide. In the intercellular space of the tomato leaf, C. fulvum secretes specific proteins, so-called effectors, which facilitate virulence of the fungus, but which, on the other hand, can also be recognised by tomato immune receptors. It becomes an avirulence (Avr) protein when such an effector is recognised. Instead of supporting virulence, the effector leads to the pathogen becoming avirulent on this host.
By studying the effector repertoire of C. fulvum, we aim to learn how pathogens can evade host recognition by, for example, mutation or even complete loss of its avirulence genes.
We also want to gain more insight into the function of specific effectors by determining their conservation in all strains of C. fulvum, their contribution to pathogen virulence, their (sub)cellular localisation, and by identifying their targets in the host.
We want to decipher how Cf resistance proteins function at the molecular level, how they get activated and how, through the co-receptors SOBIR1 and BAK1, they initiate the cytoplasmic defence signal transduction cascade leading to disease resistance. We aim to identify the interaction partners of the Cf proteins and their co-receptors study the effect of their knock-out on the resistance response. We use various molecular and biochemical techniques, like proximity-dependent labelling, co-immunoprecipitations, gene silencing and CRISPR/Cas technology. For such experiments, we use the tobacco variety Nicotiana benthamiana, as it is a very versatile model for Solanaceous plants in the lab.
Concerning tomato, we aim to identify novel immune receptors that facilitate the recognition of essential conserved effectors of C. fulvum. These findings will provide crucial fundamental knowledge on pathogen-host co-evolution. Plant breeders could and should apply this knowledge to develop novel, more durable forms of genetic resistance, contributing to world food security.