Heterologous Expression of Sorghum bicolor PIP1-3 Gene Improves Drought Tolerance in Arabidopsis and Rapeseed

Aquaporins are key membrane proteins that mediate water transport in plants and are indispensable for maintaining cellular water homeostasis and normal physiological processes. This study investigated the function of <i>SbPIP1-3</i>, an aquaporin gene isolated from drought-tolerant Sorghum bicolor. Bioinformatics analysis, subcellular localization, and heterologous expression of <i>SbPIP1-3</i> were performed in <i>Saccharomyces cerevisiae</i>, <i>Arabidopsis thaliana</i>, and rapeseed. Sequence analysis revealed that SbPIP1-3 encodes a basic hydrophobic protein targeted to the plasma membrane, a finding further corroborated by subcellular localization assays. In yeast expression assays, <i>SbPIP1-3</i>-transformed strains retained viability under osmotic stress induced by 1.2 M mannitol, whereas non-transgenic control strains failed to survive. In <i>Arabidopsis</i> and rapeseed experiments, the <i>SbPIP1-3</i> overexpression enhanced drought tolerance (improved germination, root growth, antioxidant enzyme activity, proline content, PSII repair capacity, and survival after drought-rewatering) and reduced intracellular H₂O₂ accumulation. Transcriptome profiling of drought-stressed transgenic <i>Arabidopsis</i> and control plants demonstrated significant upregulation of mostly stress-responsive pathways (e.g., MAPK signaling pathway and hormone signaling pathways) and key drought-tolerance genes (e.g., <i>SNRK2-2</i>, <i>SOD1</i>, <i>APX3</i>, <i>GPX3</i>, <i>P5CS1</i>). Collectively, these findings suggest that <i>SbPIP1-3</i> enhances plant drought tolerance through the following mechanisms: improving transmembrane water transport efficiency to sustain cellular osmotic balance; activating the antioxidant defense system to increase enzyme activity and mitigate reactive oxygen species (ROS) accumulation; optimizing photosynthetic protection mechanisms to preserve the structural and functional integrity of PSII; and regulating the expression of stress-responsive signaling pathways and associated functional genes.