Host organelles and transporters in underground plant-pathogen interactions

Abstract

This thesis covers studies of three different soilborne plant pathogens, the two fungi, Rhizoctonia solani and Verticillium longisporum, and the protist Plasmodiophora brassicae, as well as their host responses. Based on genome sequence analysis of the pathogens and their plant hosts, different effectors and plant defence factors were predicted. Follow-up molecular studies revealed the following: In sugar beets, two genes encoding major latex protein-like (MLP) family members, MLP1 and MLP3, contribute to the defence against R. solani. The small cysteine-rich effector RsRCP1 was highly induced in the fungus upon infection. RsRCP1 was localized to chloroplasts and mitochondria in the leaves of Nicotiana benthamiana. An additional MLP gene in oilseed rape, MLP6, was found to provide elevated levels of defence to V. longisporum together with a nitrate/peptide transporter family protein (NPF5.12). Recognition of the fungus triggered nitrate starvation and MLP-mediated defence, together reducing the lipophilic suberin barrier in the endodermal cell walls. In the genome of the clubroot pathogen P. brassicae, a consensus sequence led to the identification of peroxisomal targeting effectors. Arabidopsis mutants with impaired peroxisomal biogenesis demonstrated the importance of the plant peroxisomal transport proteins for P. brassicae establishment in the root. Host peroxisomal proteins embodied in the resting spores were also identified using a transgenic peroxisomal marker line of Arabidopsis. New technological advances and possibilities for genetic engineering of these three pathogens would greatly contribute to a deeper understanding of these different pathological systems.