<scp>HSP70</scp> as a Mediator of Host–Pathogen Interaction in <scp><i>Arabidopsis thaliana</i></scp> During <scp><i>Plasmodiophora brassicae</i></scp> Infection

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.