Pear Stigmatic Exudate microRNAs as Next-Generation Anti–Fire Blight Biocontrols: Cross-Kingdom Mechanisms Targeting Erwinia amylovora, Technical Barriers, and Translational Pathways for IPM

Fire blight, caused by the gram-negative bacterium Erwinia amylovora, represents a devastating pathogen affecting pome fruit production globally, with limited efficacy of conventional control strategies and the emergence of antibiotic-resistant strains necessitating alternative management approaches. Recent investigations into plant-derived antimicrobial factors have revealed the presence of microRNAs (miRNAs) within reproductive tissue exudates, opening novel avenues for understanding pathogen-host interactions and developing bio-inspired antimicrobial agents. The stigmatic exudates of pear (Pyrus spp.), the primary infection site for E. amylovora, constitute a biochemically complex milieu enriched in miRNAs with potential bacteriostatic or bactericidal properties. This review summary synthesizes emerging evidence regarding the identity, abundance, and functional characterization of stigma-derived miRNAs and their hypothetical mechanisms of action against fire blight pathogenesis. MicroRNAs recovered from pear stigmatic secretions exhibit sequence homology with endogenous plant regulatory molecules implicated in defense and stress response pathways, suggesting conserved antimicrobial functions. In vitro bioassays indicate that certain miRNA species directly suppress virulence gene expression in E. amylovora or compromise bacterial membrane integrity through cross-kingdom regulatory mechanisms. The temporal dynamics of miRNA accumulation in stigmatic exudates coincide with periods of heightened pathogenic susceptibility, proposing a natural correlation between reproductive phenology and chemical defense architecture. Extraction and stabilization protocols for stigma-derived miRNAs present considerable technical challenges, encompassing RNA degradation kinetics and maintenance of biological activity under variable environmental conditions. Comparative analysis of miRNA profiles across pear cultivars with differential fire blight susceptibility may elucidate genotype-specific exudate chemistry and inform breeding strategies. Current limitations impede the transition from fundamental characterization to practical biocontrol formulation, including incomplete understanding of miRNA bioavailability, persistence in phyllosphere environments, and potential phytotoxic effects on non-target organisms. Regulatory frameworks governing biological agents derived from plant exudates remain underdeveloped within most jurisdictions. This abstract examines the molecular mechanisms underlying potential antimicrobial efficacy, synthesizes methodological advances in miRNA isolation and characterization, and identifies critical knowledge gaps. Integration of stigma-derived miRNAs into integrated pest management systems could provide sustainable alternatives to chemical fungicides whilst leveraging innate plant defense chemistry, contingent upon rigorous field-level validation and standardized production methodologies