Quorum-Sensing Signal Molecule C10-HSL Exhibits a Cross-Kingdom Inhibition Effect on Phytophthora sojae

AHL quorum sensing signal molecules of bacteria are involved in regulating the inhibition effect of biocontrol agents on several plant diseases. However, the direct inhibition effect of AHL on pathogens and the molecular mechanism of inhibition remain unclear. Phytophthora root rot of soybean (PRR), caused by Phytophthora sojae, is a devastating oomycete disease in soybean production. To investigate the application potential of AHL in the PRR control, zoospore chemotaxis, oospore formation, mycelial growth, and pathogenicity in P. sojae responding to AHL were determined. The transcriptome of P. sojae in response to AHL was also analyzed. The key differentially expressed genes (DEGs) were quantitatively verified by qRT-PCR. We found that C10-HSL was the most abundant AHL in the fermentation broth biocontrol strain Pseudomonas mandelii. C10-HSL repels P. sojae zoospores, inhibits P. sojae mycelial growth and oospores formation, and alleviates the pathogenicity of P. sojae. The inhibition effect was regulated mainly by nitrogen metabolism, efferocytosis, glycolysis/gluconeogenesis, carbon metabolism pathways. P. sojae cell structures could disrupt and carbohydrate utilization could interfere during the response process. This result reveals that C10-HSL acts as a cross-kingdom signaling molecule to inhibit P. sojae and control PRR.