Reduction of Plasmodiophora brassicae Infection on Brassica rapa Through Host-Induced Gene Silencing of Two Secreted Genes

Abstract Clubroot disease, caused by the biotrophic pathogen Plasmodiophora brassicae, poses a significant threat to global cruciferous crops production. Current prevention and control strategies are ineffective against P. brassicae. Therefore, new control approach is needed. We have identified two putative effectors, Pb48 and Pb52, which possess secretory functions and exert influence on plant defense. Instantaneous expression of hairpin RNAi constructs with sequence homology to P. brassicae effector Pb48 or Pb52 was performed in Brassica rapa. The successful expression in host and their uptake by P. brassicae were confirmed through observation of green fluorescence in root hair and root epidermal cells as well as within P. brassicae zoosporangia. Successful silencing of either Pb48 or Pb52 resulted in reduced root gall size and enhanced resistance of the host to P. brassicae infection. Especially, silencing of Pb48 led to a decrease in zoosporangia numbers within root hair and epidermal cells. Silencing either Pb48 or Pb52 also resulted in decreased expressions of cytokinin biosynthesis gene IPT1 and auxin homeostasis GH3.5 associated with hormone regulation pathways involved in clubroot development. The transient expression of short interfering RNAs from P. brassicae demonstrates its potential as an effective strategy against this pathogen, thereby paving the way for future developments that confer disease resistance to susceptible host.