How Does Plasmodiophora brassicae Manipulate Its Host Development and Metabolism?

Plasmodiophora brassicae (Clubroot) is an intracellular biotrophic pathogen responsible for clubroot disease in Brassicaceae plants, such as Brussels sprouts and oilseed rape, which significantly impact crop production. However, the interactions between the pathogen and its host remain poorly understood. Little is known about the chemical nature of the nutrient compounds and the pathogen transporters involved in their uptake from host plants. While P.brassicae is believed to produce cytokinins (CK) during disease development, studies on phytohormone levels in infected plants have yielded mixed results.
In this thesis, I utilised bioinformatics approaches to identify potential P.brassicae transporters involved in nutrient acquisition from the host. I show that most existing P.brassicae gene models are inaccurate and require experimental validation before genomic data can be used for functional studies. I also demonstrate that a large portion of the P.brassicae genome is dedicated to encoding transporters belonging to various transport systems and families, particularly when compared to other obligate biotrophic pathogens. Moreover, I identify a novel class of transporters that is not common in eukaryotes, including two transporters in the SWEET family. These transporters are expressed at different stages of P.brassicae development and may provide the pathogen with a competitive advantage over its host.
Lastly, I employ genetic approaches to explore the role of P.brassicae IPT genes during disease development. I reveal that these IPT genes belong to the tRNA-IPT class and that both P.brassicae infection and the overexpression of IPT genes in Arabidopsis lead to CK-specific phenotypes. Together, these findings and the P.brassicae genome annotation resource developed in this thesis provide a solid foundation for future research on the role of P.brassicae nutrient transporters, the CK produced by the pathogen, and the broader function of IPT genes in the development of clubroot disease.