Transcriptomic and metabonomic analysis of quorum sensing signal (N-octanoyl-DL-homoserine lactone) on regulating poplar fine roots growth

Root-microbe transboundary communication is important to dominate the interaction between plant and microorganism. However, the influence of quorum sensing signals among bacteria community on the root growth and development is still obscure. The study focused on one quorum sensing signal isolated from poplar rhizosphere, N -octanoyl-DL-homoserine lactone (C8-HSL), and examined its influence on the morphological structure, ultrastructure, and subcellular structure of poplar roots. Transcriptome and metabolome sequencing were further performed to reveal the potential mechanisms of C8-HSL regulating the root morphological development. The results showed C8-HSL demonstrated dual regulatory effects on the growth of poplar fine roots. At high concentrations (more than 100 μM), root growth of poplar seedlings was suppressed by C8-HSL, and the primary and lateral roots appeared short and thick. Conversely, at low concentrations (10 nM), root growth was promoted by C8-HSL, and the primary and lateral roots were elongated. Fluorescent probes indicated that Ca 2+ , reactive oxygen species (ROS), and nitric oxide (NO) in root tip cells were significantly up-regulated at concentrations more than 1 μM of C8-HSL, while only Ca 2+ and NO concentration were significantly up-regulated at concentrations less than 1 μM of C8-HSL. Transcriptome and metabolome analysis further revealed that high concentration C8-HSL significantly upregulated the expression of poplar genes related to secondary wall biogenesis (e.g., MYB46 , MYB83 , CESA ) and auxin transport (e.g., PIN6 , AUX22B , GH3.6 ). In contrast, low concentration C8-HSL upregulated calmodulin expression and increased indoleacrylic acid and 3-indolebutyric acid content. Taken together, these findings provide a deeper insight to the interaction between root and microbes, and imply the potential utilization of quorum sensing signals in regulating root growth. • C8-HSL exhibits dual regulation of poplar fine root growth. • High C8-HSL suppresses root growth and triggers secondary wall deposition. • High C8-HSL increases Ca 2+ , ROS, NO; low increases only Ca 2+ , NO in root tip cells. • Low C8-HSL promotes root growth by involving indoleacrylic acid, 3-indolebutyric acid.