Molecular mechanism of nanochitin whisker elicits plant resistance against Phytophthora and the receptors in plants

Rod-like nanochitin (NC) whisker with cationic nature has a strong synergistic effect with fungicides on inhibition of tobacco root rot disease. This study we explored the activity of NC against Phytophthora and the mechanism for eliciting plant defense response and the receptors in planta. P. capsici isolates, model Nicotiana benthamiana plants and Arabidopsis thaliana were treated with 0.005% of NC suspension and 1 μM of flg22. Infection control efficacy against P. capsici isolates, biosynthetic enzyme activities and the PR genes expression were determined at different hours post treatment in plant. The infection control efficacy, ROS generation, and PTI maker gene expression were re-analyzed in A. thaliana Col-0, bak1 and cerk1 mutants. The results showed that NC did not exhibit inhibitory effect on vegetative growth of P. capsici, but enhanced the resistance against P. capsici by systemically enhanced phenylalanine ammonia-lyase activity and PR gene expression. P. capsici resistance, PTI maker gene promotion, and ROS production in A. thaliana induced by NC depended not only on chitin receptor CERK1, but also BAK1. NC and flg22 induced oomycete immunity through a mechanism of a cross-microbe protection via the BAK1-CERK1 pathway in plant, pointing to the complexity of the plant immunity system.