The extrahaustorial membrane of barley powdery mildew – new insights into transport mechanisms and membrane characteristics

Research output: Book/ReportPh.D. thesisResearch

Plant pathogens are a feared threat in agriculture and lead to immense yield losses every year. This does not only translate to financial losses, but also to people starving. Additionally, more and more pesticides are taken from the market due to health concerns, leaving farmers with fewer and fewer options to protect their plants. The changing climate is another challenge, as plant pathogens that were limited to an area before, are now able to spread due to expanding favourable conditions. Therefore, the demand is high for stable, efficient and durable resistances in plants. In order to identify possible targets and mechanisms that translates into resistant plants, knowledge about internal processes and mechanisms in plant-pathogen interaction is crucial. In this PhD thesis, I focused on Blumeria graminis f. sp. hordei, a powdery mildew fungus, infecting barley (Hordeum vulgare). This pathogen not only leads to yield losses, but is also a well-studied biotroph fungus, being used as a model organism in the last few decades. After successful penetration of an epidermal leaf cell, the fungus develops a structure, the so-called haustorium, inside the host plant. This haustorium is surrounded by a host-derived membrane, the extrahaustorial membrane (EHM), enclosing the extrahaustorial matrix (EHMx). The powdery mildew EHM is unique and enigmatic, and the purpose of this thesis is to identify mechanisms of transport across the EHM and to learn more about the composition of it. I was able to show that the isoelectric point (pI) of proteins influences their translocation across the EHM, with a pI between 6.0 – 8.4 favouring a translocation to the EHMx. These findings are based on previous results showing a selective translocation of proteins to the EHMx. In order to identify how this transport across the membrane is possible, I investigated if there are similarities to the nuclear import/export complex and the peroxisomal import. Our working hypothesis isthat fully functional and folded proteins are transported across the membrane. The investigation of a nuclear export signal however, did not result in any conclusive results. The peroxisome translocon, however, might be connected to the haustorium. The three RING domains involved in receptor recycling at the peroxisomal membrane are accumulating at the EHM of the powdery mildew. However, the exact function of these RING domains and how they attach to this membrane remains elusive. Lastly, I investigated the phosphatidylinositol phosphate (PIP) distribution in infected barley cells, to see if this distribution changes over time and if there are specific PIPs binding to the EHM. In this case, I was only able to confirm the differences between the plasma membrane, the tonoplast and the EHM, but none of the tested PIPs could be localized at the EHM. Summarizing, this work shows that transport across the EHM is influenced by protein properties and suggests a connection between the powdery mildew haustoria and the peroxisomes. How this connection is made and to what purpose and extent remains elusive.
Original languageEnglish
PublisherDepartment of Plant and Environmental Sciences, Faculty of Science, University of Copenhagen
Publication statusPublished - 2020

ID: 243863532