The two-spotted spider mite, Tetranychus urticae Koch, is one of the most harmful pests in many agroecosystems worldwide.  To effectively manage this pest, there is an urgent need to develop novel bio-active acaricides that support integrated pest management strategies targeting T. urticae.  In this study, we explored the acaricidal effects of xenocoumacin 1 (Xcn1) on T. urticae and its predator Neoseiulus californicus using the highly purified compound.  Xcn1 was extracted and purified from the cell-free supernatant of the Xenorhabdus nematophila CB6 mutant constructed by the easy promoter activated compound identification (easyPACId) method.  When the concentration of Xcn1 exceeded 100 μg mL^–1, the survival rate of spider mite adults declined to below 40% and the fecundity was decreased by 80% at six days post-application.  At concentrations of 25 and 50 μg mL^–1, Xcn1 significantly impeded spider mite development by inhibiting the molt.  However, neither concentration had any adverse effects on the survival or reproduction of the predatory mite N. californicus.  The results from laboratory and semi-field experiments consistently demonstrated the effectiveness of the antimicrobial metabolite Xcn1 in controlling pest mites at both the molecular and physiological levels.  Our study offers a promising possibility that combines the compatible biocontrol agents of Xcn1 and predatory mites for integrated pest mite control.

Fusarium graminearum, the primary pathogenic fungus responsible for Fusarium head blight (FHB) in wheat, secretes abundant chemical compounds that interact with host plants.  In this study, a secreted protein FgHrip1, isolated from the culture filtrate of F. graminearum, was found to induce typical cell death in tobacco.  The FgHrip1 gene was then cloned and expressed in Escherichia coli.  Further bioassay analysis showed that the recombinant FgHrip1 induced early defense induction events, such as reactive oxygen species (ROS) production, callose deposition, and up-regulation of defense-related genes in tobacco.  Furthermore, FgHrip1 significantly enhanced immunity in tobacco seedlings against Pseudomonas syringae pv. tabaci 6605 (Pst. 6605) and tobacco mosaic virus (TMV).  FgHrip1-treated wheat spikes also exhibited defense-related transcript accumulation and developed immunity against FHB infection.  Whereas the expression of FgHrip1 was induced during the infection process, the deletion of the gene impaired the virulence of F. graminearum.  Our results suggest that FgHrip1 triggers immunity and induces disease resistance in tobacco and wheat, thereby providing new insight into strategy for biocontrol of FHB.

Xenocoumacins （Xcns）, the major antimicrobial natural products produced by Xenorhabdus nematophila, have gained widespread attention for their potential application in crop protection. However, the regulatory mechanisms involved in the biosynthesis of Xcns remain poorly understood. In this study, we identified 21 potential two-component systems (TCSs) in X. nematophila CB6 by bioinformatic analysis. Among them, the response regulators (RRs) GlrR and ArcA were proven to positively regulate the production of Xcns based on gene deletion and complementation experiments. In addition, our results showed that GlrR played an important role in cell growth, while ArcA was involved in both cell morphology and growth. Using a variety of molecular biological and biochemical techniques, we found that GlrR controlled the Xcns biosynthesis by indirectly regulating the expression levels of the biosynthetic gene cluster (BGC). ArcA directly binded to the promoter regions of xcnA and xcnB to regulate the transcription of the Xcns BGC, and the binding sites were also identified. This study provides valuable insights into the regulatory network of Xcns biosynthesis, which will contribute to the construction of a high-yielding strain.