Genome- and Transcriptome-Wide Characterization of AP2/ERF Transcription Factor Superfamily Reveals Their Relevance in Stylosanthes scabra Vogel Under Water Deficit Stress

<i>Stylosanthes scabra</i>, a legume native to the Brazilian semiarid region, exhibits remarkable drought tolerance and represents a valuable model for studying molecular adaptation in legumes. Transcription factors of the AP2/ERF superfamily play central roles in plant development and stress response. This study aimed to identify and characterize AP2/ERF genes in <i>Stylosanthes scabra</i> and to analyze their transcriptional response to root dehydration. Candidate genes were identified through a Hidden Markov Model (HMM) search using the AP2 domain profile (PF00847), followed by validation of conserved domains, physicochemical characterization, prediction of subcellular localization, phylogenetic and structural analyses, and functional annotation. A total of 295 AP2/ERF proteins were identified and designated as <i>Ssc</i>AP2/ERF, most of which were predicted to be localized in the nucleus. These proteins exhibited a wide range of molecular weights and isoelectric points, reflecting structural diversity, and were classified into four subfamilies: AP2, ERF, DREB, and RAV. Functional annotation revealed predominant roles in DNA binding and transcriptional regulation, while promoter analysis identified numerous stress-related cis-elements. A total of 32 transcripts were differentially expressed under 24 h of water deficit, and four selected genes had their expression patterns validated by qPCR. These findings provide new insights into the AP2/ERF gene subfamily in <i>Stylosanthes scabra</i> and lay the groundwork for future biotechnological approaches to enhance stress tolerance in legumes.