Genome-Wide Identification of GRAS Gene Family and Drought Response Analysis of DELLA Proteins in Populus deltoides

The GRAS transcription factor family plays a pivotal role in plant stress adaptation, yet its systematic characterization and the underlying drought-responsive mechanisms remain poorly elucidated in Populus deltoides. Here, a genome-wide identification and analysis of GRAS genes in P. deltoides was performed, and a total of 92 family members were identified and classified into 12 distinct subfamilies through phylogenetic analysis. Evolutionary analysis revealed a high degree of conservation between the GRAS proteins of P. deltoides and those of Arabidopsis thaliana, Oryza sativa, and Solanum lycopersicum. Genomic duplication events, including 90 segmental and 11 tandem duplications, were identified as the primary drivers of GRAS family expansion. Promoter cis-element analysis uncovered an enrichment of stress-responsive elements (MBS, ABRE) and phytohormone-related motifs (e.g., TATC-box). Transcriptomic profiling further revealed distinct drought-inducible expression patterns of GRAS genes: PdeGRAS49 exhibited rapid upregulation at the early stage of drought exposure (1–3 h), whereas DELLA subfamily members PdeGRAS51 and PdeGRAS59 reached their expression peaks at 6–9 h, and PdeGRAS34 and PdeGRAS77 maintained sustained activation throughout 12–24 h. Moreover, the drought-inducible expression patterns of five DELLA genes were confirmed by qRT-PCR validation. Collectively, this study provides crucial genomic insights into the GRAS family and valuable candidate gene resources, which lay a foundation for molecular breeding of drought-tolerant P. deltoides cultivars via manipulating GRAS-mediated regulatory mechanisms.