Unveiling the dual role of <i>Priestia megaterium</i> VIT-2021 membrane vesicles as an antimicrobial and immunomodulator in supporting the growth of <i>Oryza sativa</i> ADT38

To increase yield and productivity, plants are treated with chemicals; however, these interventions have inadvertently contributed to a decline in food security. To mitigate these challenges, plant growth-promoting rhizobacteria (PGPRs), which increase yield, have been widely used to modulate plant immunity. Some PGPRs have recently been reported to exhibit opportunistic pathogenicity in humans, raising safety concerns regarding their widespread application. Membrane vesicles (MVs) derived from PGPR may retain similar plant growth-promoting (PGP) traits and thus could aid in plant protection. This research tests the hypothesis that MVs derived from the PGPR <i>Priestia megaterium</i> VIT-2021 as an effective and sustainable alternative for combating bacterial infection. MVs were successfully isolated and characterized, and the results ensured that these MVs are efficient antimicrobial agents against <i>Pseudomonas syringae</i>. Proteomic analysis of the MVs revealed the presence of four antimicrobial peptides AMP underlying their antimicrobial effects. Furthermore, <i>in vitro</i> treatment with these MVs downregulated <i>P. syringae</i> virulence genes, including <i>avrE</i>, <i>hrpS</i>, and <i>mgrA</i>. <i>In planta</i> experiments conducted on <i>Oryza sativa</i> demonstrated that <i>P. megaterium</i> MVs effectively reduced <i>P. syringae</i> pathogenicity through immune modulation, as evidenced by the upregulation of <i>WRKY13</i>, <i>IPA1, WKRY45, NPR1</i> and <i>PR1</i>, with fold increase of approximately 2.98, 3.55, 1.73, 2.44, and 5.51, respectively, at 4.2 × 10⁸ particle concentration. <i>WRKY13</i> is involved in SA-mediated secondary cell wall synthesis, which resists pathogen ingress. Increased <i>IPA1</i> promoted the upregulation of <i>WRKY45</i>, which could contribute to SA-mediated antimicrobial secondary metabolite synthesis. Increased expression of <i>NPR1</i> and <i>PR1</i> mediate cell wall rigidification and antimicrobial activity, ultimately contribute to robust immunity. Additionally, increased <i>IPA1</i> is associated with multiple tiller outgrowths, panicle branching, and grain size development. Thus, <i>P. megaterium</i> MVs demonstrated dual functionality of immunomodulation and growth promotion in <i>O. sativa</i>. Therefore, the current research highlights a pioneering strategy for sustainable crop protection and yield enhancement.