Bacterial effectors that manipulate the plant phosphate starvation response - understanding how they promote disease and activate plant immunity.

• Applicant: Professor Dr. Thomas Lahaye
• Subject Area: Organismic Interactions, Chemical Ecology and Microbiomes of Plant Systems
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 549250172

Plant pathogenic microorganisms such as bacteria, fungi and oomycetes alter the course of infection in their favor by introducing numerous effector proteins (effectors) into the host cells. These microbial effectors increase the susceptibility of the host (effector-triggered susceptibility [ETS]) by manipulating many different processes in the host cell. For example, many effectors suppress the basal plant immune system (PAMP-triggered immunity [PTI]) to favor infection. In the course of plant-parasite co-evolution, some plants have developed resistance proteins (R) that are able to recognize the structure or biological activity of microbial effectors and trigger an immune response (effector-triggered immunity [ETI]). The elucidation of the molecular mechanisms by which effectors increase the resistance of plants to pests and how plant proteins realize the recognition of effectors is a central topic of basic research, but also of applied plant research, since a sound understanding of these mechanisms is an essential prerequisite for the breeding of pest-resistant crops. In this context, we are analyzing the function of XopH, an effector protein of Xanthomonas euvesicatoria, a bacterial pathogen that infects tomato and bell pepper plants. Previous work has shown that XopH suppresses plant PTI. In addition, XopH has been shown to act as an enzyme in host cells that dephosphorylates plant inositol phosphates (InsPs). InsP derivatives have a phosphate storage function in plants, but are also important messengers in phosphate homeostasis. XopH also induces ETI, a reaction mediated by the pepper R protein Bs7. The aim of the present project proposal is to elucidate the molecular basis of how XopH suppresses PTI and how the R-protein Bs7 mediates the recognition of XopH. In preliminary work, we were able to show that XopH-like proteins are present in various plant-associated bacterial parasites and symbionts and that these, like XopH, trigger a Bs7-mediated immune response. We were also able to show that XopH triggers a phosphate starvation program in plants. Furthermore, we were able to clone the pepper R gene Bs7 in preliminary work and validate its functionality in complementation analyses. As part of the project proposal, we now want to clarify how XopH and XopH-like proteins suppress plant PTI by dephosphorylation of InsP derivatives. On the other hand, we want to clarify how the pepper Bs7 protein detects the presence of XopH and XopH-like proteins and subsequently triggers an immune response.

• DFG Programme: Research Grants