Regulation of plant immunity and disease susceptibility by endogenous peptides

Dr. Martin Stegmann

Plants possess a sophisticated innate immune system consisting of different layers of constitutive and induced defence mechanisms. The first induced immune response of plants against attacking pathogens is called pattern-triggered immunity and characterized by the perception of highly conserved microbe- or pathogen derived molecular signatures (so-called microbe- or pathogen-associated molecular patterns, MAMPs/PAMPs) by plasma membrane localized pattern recognition receptors (PRRs), which belong to the family of receptor kinases (RKs) or receptor-like proteins (RLPs). The on and offset of PRR signalling in response to PAMP perception is tightly regulated at different levels to avoid unwanted or excessive activation of immune responses. Interestingly, despite perceiving a multitude of different PAMPs or endogenous damage-associated molecular patterns (DAMPs), receptor kinases also play crucial functions in perceiving cues involved in growth and development. An important class of these growth-regulating signalling molecules are endogenous plant peptides. To increase complexity, there is emerging evidence that RKs involved in growth and development, together with their respective ligands, can regulate signalling by PRRs. Therefore, we are interested to identify plant signalling peptides with an influence on PAMP-triggered immune signalling, also calledphytocytokines, to unravel the underlying molecular mechanisms. Furthermore, we are studying the influence of specific plant peptides on the interaction between the host plant and adapted powdery mildew fungi to close gaps in our understanding of the molecular mechanisms regulating disease susceptibility. For this purpose, we are performing a combination of genetic, biochemical and plant phenotypic approaches using the model dicot species Arabidopsis thaliana and the monocot crop plant barley (Hordeum vulgare).

In Arabidopsis, an important RK regulating both immunity and growth is the Catharanthus roseus receptor-like kinase 1-like (CrRLK1L) FERONIA (FER), which perceives endogenous rapid alkalinisation factor (RALF) peptides and controls a multitude of processes, including pollen perception, cell elongation and root hair growth. Importantly, recent work has shown that FER serves as a RALF-regulated scaffold protein to facilitate the assembly of signalling-competent immune receptor complexes at the plasma membrane (Stegmann et al., Science 2017, Xiao et al., Nature 2019). How FER regulates and orchestrates these different phenotypic responses is still poorly understood. Despite serving as a crucial positive regulator of plant immunity, some adapted pathogens have evolved mechanisms to exploit the endogenous function of FER to cause disease. Therefore, another major interest of our research is to study the molecular mechanisms governing the regulatory function of FER in growth, immunity and disease susceptibility.

Another class of signaling peptides are called GOLVEN. We recently showed that GLV2 supports immune signaling in Arabidopsis via its RGI LRR-RLK receptors. GLV2 stimulates immune receptor complex formation and supports protein abundance of PRRs. GLV2 acts hence as a phytocytokine which regulates immune receptor abundance and thereby supports disease resistance (Stegmann et al. 2022, EMBO Rep.).