The Small Auxin Upregulated RNA PsnSAUR6 from Populus simonii × P. nigra Enhances Drought Tolerance in Transgenic Tobacco

Intensifying drought stress under global climate change poses a significant threat to woody plants, highlighting the critical need to identify key genes conferring drought tolerance. Here, we characterized PsnSAUR6, a Small Auxin Upregulated RNA (SAUR) family gene from poplar (Populus simonii × P. nigra) that is responsive to drought and abscisic acid (ABA). Overexpression of PsnSAUR6 in transgenic tobacco conferred superior drought tolerance, evidenced by increased biomass, enhanced root elongation, improved stomatal regulation, and favorable physiological responses, including higher proline content and peroxidase (POD) activity but lower malondialdehyde (MDA). Transcriptome analysis revealed that under water deficit, PsnSAUR6 suppressed the ABA negative regulator PP2C37 while upregulating key antioxidant defense-related transcription factors (ERF020, NAC83, MYB2) and the potassium transporter HAK5. Collectively, these findings establish PsnSAUR6 as a positive regulator in ABA-mediated drought adaptation, presenting it as a promising genetic target for enhancing the climate resilience of woody plants.