Paecilomyces variotii extracts (ZNC) enhance plant immunity and promote plant growth

Background and aims The crude extract of the endophyte Paecilomyces variotii known as ZhiNengCong (ZNC) has function of promoting plant growth and enhancing disease resistance and is widely used in China. Our study aims to evaluate the molecular mechanisms of plant growth promotion and disease protection. Methods We generated transcriptome profiles from ZNC-treated seedlings using RNA sequencing. The function of salicylic acid (SA) in ZNC-mediated immunity was examined using SA biosynthesis and signaling pathway mutants. The concentrations of nitrogen (N) and phosphorus (P) in seedlings under ZNC treatment were measured. The effect of ZNC on the level of the hormone auxin in roots was tested using transgenic plants containing DR5::GFP. Results ZNC exhibited ultrahigh activity in promoting plant growth and enhancing disease resistance, even at concentrations as low as 1-10 ng/ml. ZNC induced ROS accumulation, callose deposition, and expression of PR genes. SA biosynthesis and signaling pathways were required for the ZNC-mediated defense response. Moreover, in improving plant growth, ZNC increased the level of auxin in root tips and regulated the absorption of N and P. Conclusion According to these results, ZNC is a highly effective plant elicitor that promotes plant growth by inducing auxin accumulation at the root tip at low concentrations and enhances plant disease resistance by activating the SA signaling pathway at high concentrations.