Genome-Wide Identification of the ERF Transcription Factor Family for Structure Analysis, Expression Pattern, and Response to Drought Stress in Populus alba x Populus glandulosa

The Ethylene Responsive Factor (ERF) transcription factor family is important for regulating plant growth and stress responses. Although the expression patterns of ERF family members have been reported in many plant species, their role in Populus alba x Populus glandulosa, an important model plant for forest research, remains unclear. In this study, we identified 209 PagERF transcription factors by analyzing the P. alba x P. glandulosa genome. We analyzed their amino acid sequences, molecular weight, theoretical pI (Isoelectric point), instability index, aliphatic index, grand average of hydropathicity, and subcellular localization. Most PagERFs were predicted to localize in the nucleus, with only a few PagERFs localized in the cytoplasm and nucleus. Phylogenetic analysis divided the PagERF proteins into ten groups, Class I to X, with those belonging to the same group containing similar motifs. Cis-acting elements associated with plant hormones, abiotic stress responses, and MYB binding sites were analyzed in the promoters of PagERF genes. We used transcriptome data to analyze the expression patterns of PagERF genes in different tissues of P. alba x P. glandulosa, including axillary buds, young leaves, functional leaves, cambium, xylem, and roots, and the results indicated that PagERF genes are expressed in all tissues of P. alba x P. glandulosa, especially in roots. Quantitative verification results were consistent with transcriptome data. When P. alba x P. glandulosa seedlings were treated with 6% polyethylene glycol 6000 (PEG6000), the results of RT-qRCR showed that nine PagERF genes responded to drought stress in various tissues. This study provides a new perspective on the roles of PagERF family members in regulating plant growth and development, and responses to stress in P. alba x P. glandulosa. Our study provides a theoretical basis for ERF family research in the future.