Spatiotemporal Metabolic Reprogramming of Casuarina equisetifolia in Response to an Interaction-Conditioned Filtrate of the Plant Growth-Promoting Bacterium LB46

Plant growth-promoting bacteria can influence host metabolism, but live-inoculation systems confound chemical signaling with colonization, nutrient exchange, and continuous metabolite release. Here, Paenibacillus cellulositrophicus LB46 was co-cultured with sterile Casuarina equisetifolia seedlings for 5 d. After 0.22 μm filtration, the interaction-conditioned filtrate was applied to new sterile seedlings; no culturable LB46 was detected in the filtrate under the plating conditions used. Untargeted LC–QTOF-MS profiled roots after 3 and 5 d and shoots after 5 d. The filtrate induced broad metabolic remodeling, with stronger responses in roots than in shoots. A total of 473, 437, and 125 metabolites met the differential-abundance criterion (BH-FDR < 0.05) in 3 d roots, 5 d roots, and 5 d shoots, respectively; 273 root metabolites showed a significant treatment × time interaction (BH-FDR < 0.05). Temporal classification revealed pronounced turnover among early-transient, late-induced, and sustained responses. At 5 d, only 11 metabolites met the differential-abundance criterion in both roots and shoots, indicating predominantly tissue-differentiated remodeling. These results define temporally and spatially differentiated metabolic responses to the interaction-conditioned environment. Because bulk physicochemical properties of the filtrates were not characterized, the observed responses cannot be attributed exclusively to specific chemical signals.