Characterizing the Effector Repertoire of Plasmodiophora brassicae: Insights into Clubroot Pathogenesis

Abstract

Plasmodiophora brassicae, the obligate parasite responsible for clubroot in Brassica crops and other crucifers, poses a major challenge to sustainable disease management due to its biotrophic lifestyle and adaptability. Recent advances in genomics, transcriptomics, and bioinformatics have accelerated the identification of its effector repertoire, which underpins host colonization and symptom development. To date, more than 100 putative effectors have been described, including several that modulate key plant defence processes such as pattern-triggered immunity, programmed cell death, phytohormone signalling, and ubiquitin-mediated protein degradation. Despite the inability to culture or genetically manipulate P. brassicae, functional studies using heterologous systems and transgenic approaches have revealed important insights into effector activity and host-pathogen interactions. Notably, conserved effectors such as PbBSMT and PbZF1 play central roles in virulence, highlighting their potential as targets for resistance breeding and effector-informed management strategies. However, the majority of candidate effectors remain uncharacterized, and inconsistent naming conventions across studies complicate cross-comparison. This review provides the first comprehensive synthesis of current knowledge on P. brassicae effectors, aiming to classify them according to their roles in host manipulation. Effectors that are consistently expressed across life cycle stages and host systems were identified and may serve as candidates for future investigation. We also discuss methodological advances and limitations in effector discovery and functional analysis, as well as opportunities to leverage effector biology in clubroot management. Ultimately, classifying conserved versus accessory effectors and understanding their interactions with host targets will be key to developing durable resistance and innovative strategies for clubroot management.