Abstract

Brassinosteroids (BRs) are crucial plant hormones that influence growth and stress adaptation. However, the specific function of the BR receptor BRL3 under osmotic stress remains largely unexplored outside Arabidopsis thaliana. In this study, we used a CRISPR/dCas9-based transcriptional activation (CRISPRa) system to upregulate the Nicotiana tabacum BRASSINOSTEROID INSENSITIVE-LIKE 3 receptor (NtBRL3) and assessed its impact on osmotic stress tolerance. Synthetic activation vectors were constructed using Loop Assembly, featuring dCas9-6TAL-VP128 modules driven by either a constitutive (CaMV35S) or ABA-inducible (SlAREB) promoter, paired with dual sgRNAs targeting the NtBRL3 promoter. Transient Agrobacterium-mediated transformation followed by PEG treatment was used to impose osmotic stress. RT-qPCR confirmed a 3- to 4-fold activation of NtBRL3 transcripts in CRISPRa-infiltrated leaves. The stress-inducible SlAREB promoter produced the strongest improvements, yielding nearly four-fold higher leaf biomass and a five-fold increase in root biomass relative to PEG-stressed controls. Both constructs reduced malondialdehyde (MDA) accumulation, indicating diminished oxidative damage, and modulated osmoprotectant balance, including reduced root proline and increased total soluble solids, particularly under SlAREB-driven activation. Histological segmentation revealed promoter-dependent anatomical remodeling, with NtBRL3-activated plants exhibiting a higher frequency of enlarged leaf cells and expanded tissue domains, consistent with brassinosteroid-mediated structural plasticity. Collectively, these findings demonstrate that CRISPR/dCas9-mediated transcriptional activation of NtBRL3 enhances osmotic stress resilience in tobacco through coordinated biomass recovery, oxidative stress mitigation, osmolyte homeostasis, and tissue remodeling. This transient, non-integrative CRISPRa approach provides a robust synthetic biology framework for dissecting BR signaling and engineering stress-tolerant crops.