Genome-wide identification and expression profiling of the ERF subfamily in Polygala tenuifolia seedlings under drought stress

BACKGROUND: Polygala tenuifolia Willd. (P. tenuifolia) is one of the source plants of the traditional Chinese medicine 'Yuanzhi' and is widely used in clinical practice. As a meso-xerophytic medicinal plant with strong environmental adaptability, it is listed as a nationally protected wild medicinal species in China. However, the molecular mechanisms underlying its drought tolerance remain unclear. Therefore, a genome-wide identification of the ERF subfamily in P. tenuifolia was conducted to provide candidate genes for drought adaptation research and functional validation. RESULTS: Ethylene-responsive factors (ERFs) play important roles in plant responses to drought stress. In this study, 78 PtERF genes were systematically identified for the first time in P. tenuifolia. Phylogenetic analysis classified these genes into five subgroups (B1-B5), with members within the same subgroup exhibiting similar gene structures and conserved motifs. Collinearity analysis revealed that segmental duplication was the primary driving force underlying PtERF family evolution. Cis-acting element analysis revealed that PtERF promoter regions were enriched with drought-responsive cis-elements, including abscisic acid and methyl jasmonate (MeJA)-responsive elements. Transcriptome analysis combined with RT-qPCR verification identified five core drought-responsive genes, among which PtERF33 expression exhibited the highest level of upregulation. Further investigation showed that PtERF33 produced two alternatively spliced transcripts: the full-length PtERF33.1 transcript and the intron-retained PtERF33.2 transcript. These two transcripts exhibited opposite expression patterns under drought stress, suggesting that they may regulate drought responses through functional antagonism. CONCLUSIONS: These findings provide a systematic basis for identifying drought-resistant ERF genes in P. tenuifolia and establish a foundation for clarifying the role of alternative splicing in drought adaptation in this species.