Pst DC3000 volatiles reprogram Arabidopsis root architecture through ion/redox signaling, plasmodesmal gating and PIN auxin transporters

Microbial volatile organic compounds (mVOCs) provide early chemical cues of microbial activity in the rhizosphere, yet how plants translate these signals into coordinated intracellular responses and developmental outcomes remains poorly understood. Here we show that mVOCs from Pseudomonas syringae pv. tomato DC3000 (Pst DC3000) remodel Arabidopsis thaliana root system architecture (RSA) by inhibiting primary root elongation, reducing lateral root formation, and altering the lateral root gravitropic setpoint angle. Live-cell imaging revealed that Pst DC3000 mVOCs trigger rapid Ca²⁺ and K⁺ fluxes accompanied by reactive oxygen species (ROS) and nitric oxide (NO) accumulation, followed by callose deposition at plasmodesmata. Genetic and pharmacological dissection uncoupled distinct signaling modules: fls2 mutants lost the early H2O2 burst and showed delayed NO production yet retained wild-type levels of plasmodesmatal callose. This demonstrates that FLS2 functions as a genetic coordinator of early redox timing rather than a mediator of symplastic gating. In contrast, the pdko3 mutant (pdlp1/2/3) suppressed Ca²⁺, ROS and early NO responses, indicating that plasmodesmal components are essential for early signal propagation. Pharmacological inhibition of K⁺ channels eliminated callose deposition in Col-0 roots, placing K⁺ influx upstream of PDLP–PMR4-dependent plasmodesmal regulation. At the developmental level, Pst DC3000 mVOCs induced expression of PDLP2, PDLP3 and PDLP4 and reconfigured auxin signaling and PIN auxin transporter expression, including AXR1-dependent DR5 activation, transient PIN1 induction and sustained PIN3 repression, ultimately driving root architectural remodeling. Finally, the bacterial volatile 2-methylbutanoic acid partially recapitulated these effects, indicating that full RSA reprogramming depends on the combined action of multiple mVOCs.