A novel small cysteine‐rich protein, PbEL04, identified from Plasmodiophora brassicae, associates with AtSAMS2 to regulate Arabidopsis clubroot resistance

SUMMARY Plasmodiophora brassicae is a devastating intracellular pathogen that causes clubroot disease in Brassicaceae plants, leading to significant economic losses in agriculture. Enhancing plant resistance against P. brassicae has become a crucial global challenge. In this study, we report a new secreted protein, PbEL04, which can trigger cell death associated with H 2 O 2 accumulation and electrolyte leakage in the non‐host plant Nicotiana benthamiana but enhances the resistance to P. brassicae when overexpressed in Arabidopsis thaliana. Subsequently, AtSAMS2, which interacts with PbEL04, was identified in a screen of a Y2H library and confirmed by Co‐IP as well as BiFC, and the expression of AtSAMS2 was significantly increased during the cortical infection stage. Furthermore, overexpressing AtSAMS2 in Arabidopsis exhibited higher susceptibility to P. brassicae than the wild type, while the mutant showed significantly elevated resistance without affecting plant growth and development, suggesting that AtSAMS2 could be a negative factor in resistance to P. brassicae infection. Taken together, our results suggest that P. brassicae infection secretes an effector protein, PbEL04, which could interact with AtSAMS2 and affect the hormone signaling pathways to influence the formation of root swelling. Here, we discovered a new effector protein, PbEL04, and identified its host interactor, AtSAMS2, which holds great potential in plant breeding as a key genetic target for clubroot resistance.