Overexpression of OsAGO18 Promotes Early Seedling Development and Root Elongation in Rice

Argonaute (AGO) proteins are central components of RNA silencing. While OsAGO18 is a known defense factor in antiviral immunity, its involvement in basal development and its transcriptomic behavior during fungal stress remains to be fully elucidated. In this study, based on its specific dual-localization in chloroplasts and processing bodies (P-bodies), we investigated the pleiotropic effects of OsAGO18 through transcriptomic network analysis of rice responding to the blast fungus Magnaporthe oryzae B.C. Couch. Our analysis revealed that the OsAGO18-mediated co-expression network is highly correlated with ribosome biogenesis and cell wall organization. Notably, the analyzed datasets reveal that this growth-related network is significantly suppressed upon M. oryzae challenge, highlighting a transcriptomic shift in OsAGO18 during the growth-to-defense transition. Phenotypic evaluations demonstrated that OsAGO18 overexpression accelerates early seedling growth and primary root elongation by promoting endogenous indole-3-acetic acid (IAA) accumulation, whereas ago18 mutants maintain basal growth rates without significant IAA fluctuations, reflecting robust genetic compensation within the highly redundant AGO family. Mechanistically, our integrated analysis suggests that OsAGO18 acts as a putative molecular decoy to sequester miR396d, thereby relieving the repression of the Growth-Regulating Factor OsGRF6 and triggering downstream auxin-dependent cascades. Collectively, our findings highlight OsAGO18 as a pivotal regulator of early seedling development and characterize its transcriptomic responsiveness to biotic stress, providing a plausible molecular link between post-transcriptional RNA regulation and rice growth coordination.