Reduction of Plasmodiophora brassicae infection on Brassica rapa through host-induced gene silencing of two secreted genes

Clubroot disease caused by the biotrophic pathogen Plasmodiophora brassicae, is one of the most serious threats to cruciferous crops production worldwide. P. brassicae is known for rapid adaptive evolution to overcome resistance in varieties. It is urgent to establish alternative management to control P. brassicae. In this study, we identified two P. brassicae secretory proteins that were up-regulated during infection and effected plant defense. We established a method for transient expression in the roots of seedlings and demonstrated that P. brassicae could take up substances from the environment of root cells. Using a RNA interference (RNAi)-based host-induced gene silencing (HIGS) by expression of hairpin RNAi constructs with sequence homology to P. brassicae effector Pb48 or Pb52 in susceptible Brassica rapa plants enhanced host disease resistance. After silencing these two effectors, the transcription levels of cytokinin biosynthesis gene IPT1 and the regulation gene of auxin homeostasis GH3.5 were down-regulated. These results suggested that RNAi-based HIGS of effectors has a great practical application of improving crop resistance against P. brassicae and can contribute to environmentally sustainable agriculture.