A natural cyclic peptide valinomycin enhances plant resistance by immune-priming

The intensive research has led to the identification of various natural compounds as alternative and/or complementary agents for the chemical management of plant diseases.Here, we propose that valinomycin, a cyclic peptide produced by Streptomyces bacillaris S8, is a putative multifunctional biocontrol agent against various plant pathogens.The compound acts as an antifungal agent against several plant pathogenic fungi, including Botrytis cinerea (B.cinerea), a necrotrophic pathogen that causes gray mold.Intriguingly, valinomycin can also boost plant immunity with priming activity in response to pathogen infection.Valinomycin-treated plants demonstrated increased flg22-mediated ROS burst, MAPK phosphorylation, and callose deposition, which are hallmarks of PAMPs-triggered immunity (PTI).Regarding effector-triggered immunity (ETI), valinomycin potentiated hypersensitive response (HR), a representative phenotype of the ETI responses.Furthermore, ROS burst assay revealed that valinomycin simultaneously facilitated PTI and ETI that mutually strengthen each other.Both locally and systemically, treatment of valinomycin enhanced the resistance against Pseudomonas syringae pv.tomato DC3000 (Pto DC3000), without direct antibacterial activity.Transcriptional analysis shows that valinomycin treatment upregulated salicylic acid-related genes, while downregulating jasmonic acid-related genes.Therefore, our study demonstrates that valinomycin harbors potential as a biocontrol agent suppressing complex pathogen infections with versatile functions.