Planococcus dechangensis NEAU-ST10-9T Promotes Maize Seedling Root Development: Evidence from Effective Fluorescence Tracking

Understanding the interaction between plants and rhizosphere microorganisms is critical for the development of biofertilizers. Fluorescent labeling of rhizosphere microorganisms serves as a key strategy to track their behavior during plant–microbe coculture. However, most newly isolated strains are novel and lack available molecular tools for such studies. In this research, Planococcus dechangensis NEAU-ST10-9T (P. dechangensis NEAU-ST10-9T), a salt-tolerant strain, was obtained from the China General Microbiological Culture Collection Center (CGMCC). It significantly increased maize root length by approximately 1.56-fold. To investigate the underlying mechanism, a donor strain (Ec102) and a shuttle plasmid (pAS104) were engineered to mediate conjugation with P. dechangensis NEAU-ST10-9T and drive GFP overexpression in the bacterium, generating the genetically labeled strain Pd103. The fluorescence intensity (expressed as GFP/OD600, arbitrary units) of Pd103 increased with bacterial growth and was approximately tenfold higher than that of the wild-type strain after 16 h of culture. Following inoculation onto maize seeds, confocal microscopy analysis revealed that Pd103 colonized the epidermis and endodermis of maize roots. These results indicated that P. dechangensis NEAU-ST10-9T could invade maize roots and promote maize seedling growth. In summary, we have successfully established a robust fluorescence labeling and tracking system tailored for P. dechangensis NEAU-ST10-9T, which constitutes a valuable tool for elucidating the cellular and molecular mechanisms governing its plant–microbe interaction.