The <scp>SCARECROW</scp>‐<scp>LIKE</scp> transcription factor from <i>Populus davidiana</i> × <i>P. bolleana</i> simultaneously improved drought tolerance and plant growth through acetylation‐dependent mechanisms

The GAI-RGA-and-SCR (GRAS) family of plant-specific transcription factors (TFs) is essential for development and stress tolerance, but their role in drought resistance and growth remains unclear. Here, we characterized the SCARECROW-LIKE (SCL) TF PdbSCL1 from Populus davidiana × P. bolleana, examining its role in drought response and growth. Overexpression of PdbSCL1 improved drought tolerance and growth, while knockout lines exhibited decreased drought tolerance and growth. Under normal conditions, overexpression lines showed a 16.7% increase in height and 14.6% in fresh weight compared with wild-type (WT). Under drought conditions, these increases reached 32.2% and 79.5%, respectively. PdbSCL1 regulates gene expression by binding to DNA motifs such as ABRE ('CACGTG'), PCF ('TGGGCC'), and NFY ('CCAAT'). Drought-induced acetylation of PdbSCL1 at key lysine residues (106 and 444) is critical for its regulatory function. Mutations at these sites impair its ability to regulate gene expression, leading to reduced drought tolerance and growth. PdbSCL1 also interacts with a histone acetyltransferase 3 (PdbHAG3), which catalyses its acetylation, further enhancing drought resilience and growth. These findings highlight the essential role of PdbSCL1 acetylation in both drought response and growth promotion, suggesting its potential application in molecular breeding to improve drought tolerance and growth in poplar.