Soybean roots recruit plant-beneficial <i>Pseudomonas</i> via secreting 3,4-dihydroxybenzaldehyde

Rhizosphere microbiota mediate plant defense against soil-borne diseases, yet the mechanisms by which resistant soybean cultivars assemble protective microbiomes remain poorly understood. Using metagenomics, metabolomics, in vitro assays, and genetic approaches, we compared near-isogenic lines (Williams82, resistant; Williams, susceptible) to dissect plant-metabolite-microbe interactions mediating Phytophthora root rot resistance. Transplanting rhizosphere soil from the resistant cultivar to susceptible plants significantly reduced Phytophthora root rot severity, correlating with Pseudomonas enrichment and accumulation of the key rhizosphere metabolite 3,4-dihydroxybenzaldehyde. We isolated a core beneficial strain, Pseudomonas parafulva ZY6, from the resistant rhizosphere. In vitro, 3,4-dihydroxybenzaldehyde treatment promoted ZY6's biofilm formation, motility, and growth, while inhibiting Phytophthora sojae at higher concentrations. Knockout and overexpression of GmTL29 via hairy root transformation altered rhizosphere levels of 3,4-dihydroxybenzaldehyde, which in turn modulated the colonization of ZY6, the abundance of P. sojae, and the relative abundance of beneficial taxa such as Pseudomonas. Exogenous 3,4-dihydroxybenzaldehyde (0.1 μmol g-1 soil) significantly reduced Phytophthora root rot disease index, increased rhizosphere bacterial diversity, and enriched Bacillus and Pseudomonas. Our study demonstrates that resistant soybeans shape a disease-suppressive rhizosphere, in which 3,4-dihydroxybenzaldehyde contributes as a prebiotic by selectively enriching beneficial microbes. These findings offer a metabolite-based strategy to engineer rhizosphere communities for sustainable soil-borne disease management.