Multi-omics and field experiments reveal the mechanism of Pseudomonas palleroniana P6 promoting the growth and polyphyllins accumulation in Paris polyphylla.

Paris polyphylla (P. polyphylla), a medicinal herb valued in traditional Chinese medicine, struggles with slow growth rate and long maturation periods, hindering sustainable cultivation and commercial production-especially for polyphyllins, its key bioactive compounds. Although plant growth-promoting rhizobacteria (PGPR) have shown potential in enhancing crop productivity and secondary metabolite accumulation, their application in slow-growing medicinal plants like P. polyphylla remains underexplored.  RESULTS: In this study, 25 strains with inorganic phosphorus-dissolving, potassium-solubilizing and nitrogen-fixing abilities were isolated from the rhizosphere soil of P. polyphylla, mainly belonging to Bacillus, Pseudomonas, and Rhizobium. Among them, the strain Pseudomonas palleroniana P6 exhibited the best growth-promoting effect on grass. The whole genome analysis demonstrated that P. palleroniana P6 could promote forage growth by secreting phosphatases, organic acids, and producing substances like IAA and siderophore. Field experiments were carried out to further validate the impact of P. palleroniana P6 on the growth of P. polyphylla. The results revealed that P. palleroniana P6 remarkably enhanced the biomass of P. polyphylla root and the content of polyphyllin I, II, and VII, and significantly increased the soil available potassium content. The transcriptome results indicated that the application of P. palleroniana P6 considerably increased the expression of genes related to the plant hormone signal transduction pathway involved in growth regulation, cholesterol synthesis, terpenoid backbone synthesis and the energy metabolism pathway associated with polyphyllins synthesis in P. polyphylla.  CONCLUSIONS: This study systematically investigated the growth-promoting effects and secondary metabolic regulation mechanisms of the bacterial inoculant P. palleroniana P6 on the endangered medicinal plant P. polyphylla. The findings highlight the potential of P. palleroniana P6 in promoting plant growth and enhancing polyphenol accumulation in P. polyphylla, providing valuable insights for the application of microbial inoculants in enhancing the growth and bioactive compound production of perennial medicinal plants.