Genome-Wide Identification and Expression of the ERF Gene Family in Populus trichocarpa and Their Responses to Nitrogen and Abiotic Stresses

The ethylene response factor (ERF) family is a prominent plant-specific transcription factor family, which plays a crucial role in modulating plant growth and stress tolerance. In this study, a total of 210 <i>ERFs</i> were identified in <i>Populus trichocarpa</i>, comprising 29 AP2 (APETALA2) subfamily members, 176 ERF subfamily members, and 5 RAV (related to ABI3/VP1) subfamily members. The duplication events of the <i>PtERF</i> family members exclusively occurred within the subfamilies. A total of 168 duplication pairs were found among 161 <i>PtERF</i> genes, and all of them were fragment duplications. Gene structure analysis revealed that most ERF subfamily members only had one exon without introns, the AP2 subfamily members had six or more introns and exons, and RAV subfamily members lacked introns except for <i>PtERF102</i>. Considerable cis-acting elements associated with plant growth and development, stress response, hormone response, and light response were detected in the promoters of <i>PtERF</i> genes. The expression levels of <i>PtERFs</i> were highest in roots across tissues and in winter among seasons. Furthermore, the nitrate and urea stimulated the expression of <i>PtERF</i> genes. The co-expression network analysis based on <i>PtERFs</i> indicated their potential roles in hormone signaling, acyltransferase activity, and response to chemicals. This study provides novel insights into investigating the role of <i>PtERFs</i> in environmental stress in poplar species.