Plasmodiophora brassicae is one of the most devastating threats to Brassicaceae crops. However, the molecular mechanisms underlying clubroot disease remain unclear. Initial proteomics results led us to hypothesize that HSP70 proteins regulate host-P. brassicae interactions by modulating both plant defenses and pathogen activity. Using the Arabidopsis thaliana-P. brassicae model system, we studied the role of HSP70 proteins in detail. Through a combination of proteomics and mutant phenotype analyses, we indicate that Plasmodiophora infection induces HSP70 accumulation in Arabidopsis roots, and mutations in specific HSP70 isoforms either promote (HSP70-1, HSP70-13, HSP70-14) or suppress (HSP70-5, HSP70-12) the onset of clubroot disease. Proteomic profiling of root galls showed strong correlations between infection severity and pathogen-derived HSP70 protein CEO96729. Interactomics analyses revealed that CEO96729 interacts with host proteins involved in plant response to Plasmodiophora infection, including an extracellular GDSL esterase/lipase with a putative role in long-distance signaling, and that CEO96729 forms heterodimers with host HSP70 isoforms. These findings suggest that Plasmodiophora hijacks the host chaperone machinery to facilitate infection, offering a potential explanation for the observed modulation of disease progression in HSP70 mutants. Notably, the results also point to possible intracellular interactions with key enzymes in host physiology, including catalase 2, essential for ROS metabolism, and nitrilase, critical for auxin biosynthesis and root gall formation. Collectively, our study highlights the multifaceted roles of HSP70 proteins in Plasmodiophora pathogenicity and host-pathogen interactions, providing insights into chaperone-mediated processes in plant immunity and infection dynamics.

• Keywords
• clubroot disease, interactomics, plant immunity, plant‐pathogen interaction, proteomics,
• MeSH
• Arabidopsis * parasitology   genetics   metabolism   MeSH
• Host-Pathogen Interactions * physiology   MeSH
• Plant Roots parasitology   metabolism   genetics   MeSH
• Mutation MeSH
• Plant Diseases * parasitology   immunology   MeSH
• Plasmodiophorida * physiology   MeSH
• Arabidopsis Proteins * metabolism   genetics   MeSH
• HSP70 Heat-Shock Proteins * metabolism   genetics   MeSH
• Proteomics MeSH
• Gene Expression Regulation, Plant MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Arabidopsis Proteins * MeSH
• HSP70 Heat-Shock Proteins * MeSH

Pythium oligandrum is a unique biological control agent. This soil oomycete not only acts as a mycoparasite, but also interacts with plant roots and stimulates plant defense response via specific elicitors. In addition, P. oligandrum can synthetize auxin precursors and stimulate plant growth. We analyzed the secretomes and biochemical properties of eleven Pythium isolates to find a novel and effective strain with advantageous features for plants. Our results showed that even closely related P. oligandrum isolates significantly differ in the content of compounds secreted into the medium, and that all strains secrete proteins, amino acids, tryptamine, phenolics, and hydrolytic enzymes capable of degrading cell walls (endo-β-1,3-glucanase, chitinase, and cellulase), exoglycosidases (especially β-glucosidase), proteases, and phosphatases. The most different strain was identified as a not yet described Pythium species. The changes in metabolism of Brassica napus plants grown from seeds coated with the tested Pythium spp. were characterized. Enhanced levels of jasmonates, ethylene precursor, and salicylic acid may indicate better resistance to a wide variety of pathogens. Glucosinolates, as defense compounds against insects and herbivores, were enhanced in young plants. Altogether, P. oligandrum strains varied in their life strategies, and either they could perform equally as plant growth promoters and mycoparasites or they had developed one of these strategies better.

• Keywords
• Pythium, cultivation medium, enzyme activities, phytohormones, plant metabolism, rapeseed, secretome,
• Publication type
• Journal Article MeSH