Fathoming the mechanistic details of ShRK signaling in the interaction of Arabidopsis thaliana and the obligate biotrophic oomycete Hyaloperonospora arabidopsidis

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Plants are in continuous exchange with their environment, yet they are unable to move in case they face adverse conditions. Receptor kinases (RKs) consist of an extracytoplasmic sensor domain that is connected to a cytoplasmic kinase domain, and link the outside of a cell with the inside. Thereby RKs enable plants to translate extracellular cues across the plasma membrane and to initiate specific signaling cascades in response to exogenous and endogenous stimuli. Consequently, this results in the adaption of the plant to its’ environment to overcome unfavorable situations like pathogen attack or nutrient scarcities. Members of the LRR-I family of RKs possess an extracytoplasmic proportion composed of leucine-rich repeats (LRRs) followed by a N-terminal malectin-like domain (MLD) comprising one or two complete or truncated malectin motifs (MLD-LRR-RKs). Previously, we identified two MLD-LRR-RKs, ShRK1 and ShRK2, which are implicated in the accommodation of the obligate biotrophic oomycete and causing agent of downy mildew disease Hyaloperonospora arabidopsidis (Hpa) in Arabidopsis thaliana leaves. We could demonstrate that ShRK1 and ShRK2 are involved in the reproductive success of the pathogen and contribute to the formation of pyriform haustoria. To this day, the precise signaling mechanisms of MLD-LRR-RKs in general and ShRKs in particular are, however, still obscure. It is completely elusive how ShRKs impact oomycete development and cellular signaling. To shed light on MLD-LRR-RK signaling and regulation, we will employ biochemical, genetic, and cell biology approaches and focus on the role of ShRKs in the Arabidopsis-Hpa interaction. We will investigate the involvement of the different ShRK modules in signal transduction and their contribution to protein regulation, study the spatio-temporal regulation of ShRKs, identify and characterize direct ShRK interactors, and inspect ShRK-mediated changes in gene expression during Hpa infection. With this we will on the one hand shed light on the molecular aspects of the Arabidopsis-Hpa association, which will help to understand and manipulate this noxious plant-microbe interaction. As agriculturally relevant crops suffer from oomycete infection that causes yield loss as well, this research – in the long run - might constitute an important aspect in the development of a sustainable and future-oriented agriculture. On the other hand, we will provide insight into MLD-LRR-RK signaling and regulation in general, which will pave the way for future research focusing on the diverse processes this highly interesting and under-studied protein family is involved in.