Abstract: Fertilizer synergists are functional additives that enhance fertilizer efficiency, regulate nutrient transformation, and improve nutrient utilization by plants. As a result, they can increase crop productivity and quality while mitigating agricultural non-point source pollution. In this study, Arabidopsis thaliana (L.) Heynh. and Brassica napus L. were used to evaluate a newly developed Harpins recombinant signal protein, designated Ralstonia signal protein (RH1), which was incorporated into a compound fertilizer to generate an RH1-enhanced formulation. Application of the RH1 synergistic compound fertilizer markedly promoted plant growth and development. Compared to the control group, A. thaliana demonstrated substantial increases in total biomass, aboveground biomass, belowground biomass, and root length of 80.94%, 80.65%, 82.95%, and 79.80%, respectively. Corresponding increases in B. napus reached 76.57%, 74.16%, 95.78%, and 39.15%, respectively. Moreover, treatment with RH1 synergistic compound fertilizer increased inorganic phosphorus content in both aboveground and belowground tissues of the two species and upregulated expression of genes involved in phosphorus uptake and transport. Field experiments further showed that application of 600 kg of RH1 synergistic compound fertilizer per hectare achieved the most pronounced yield improvement, with increases of 58.05% in 'Kaiyu 118' and 28.66% in 'Huayouza 62', respectively. These findings indicated that RH1 functioned as an effective fertilizer synergist with substantial potential to improve phosphorus utilization and crop yield.