OsBRP1 acts as a regulator of rice development and salt stress response rather than canonical general transcription factor

• OsBRP1, a rice-specific TFIIB-related protein, localizes to the ER and lacks interaction with OsTBPs, suggesting it no longer functions as a canonical general transcription factor. • Functional analyses show OsBRP1 enhances grain productivity and salt tolerance by regulating proline biosynthesis, ROS scavenging, and Na⁺ homeostasis. • Transcriptomic profiling reveals OsBRP1 coordinates gene networks involved in growth, DNA repair, auxin signaling, and stress responses, highlighting its neofunctionalization in plant adaptation. Transcriptional initiation in eukaryotes depends on general transcription factor (GTFs), among which TFIIB serving as a core component of the Pol II pre-initiation complex (PIC) assembly. While most eukaryotes possess only two conserved TFIIB paralogs, plants exhibit remarkable expansion of TFIIB-related proteins, indicating functional divergence. Here, we characterize OsBRP1, a plant-specific TFIIB-related protein in rice, and reveal its critical function in coordinating reproductive development and salt stress tolerance. Expression profiling and GUS staining showed that OsBRP1 is preferentially expressed in reproductive tissues. Subcellular localization analysis revealed a unique Endoplasmic Reticulum (ER) retention mechanism via its N-terminal domain. Yeast two-hybrid (Y2H) and bimolecular fluorescence complementation (BiFC) indicate that OsBRP1 is not involved in the formation of PIC. CRISPR/Cas9-generated mutants exhibited reduced plant height, grain size, and salt tolerance, while OsBRP1-overexpressing (OE) lines showed enhanced agronomic traits and significant resistance to salt stress. Physiological analyses demonstrated that OsBRP1 modulates proline biosynthesis, suppresses oxidative damage, and maintains Na + homeostasis under salinity. RNA-seq analysis revealed that under normal conditions, OsBRP1 could influence DNA repair, detoxification, and auxin signaling. Salt stress amplifies these effects, upregulating stress-responsive genes while downregulating genes related to photosynthesis and ROS scavenging. KEGG enrichment highlighted roles in phenylpropanoid biosynthesis, plant-pathogen interaction, and photosynthesis. Together, our results support that OsBRP1 acts as a regulator of reproductive development and salt stress response rather than canonical general transcription factor, offering new insights into plant gene evolution.