Identification of AP2/ERF Transcription Factors and Characterization of AP2/ERF Genes Related to Low-Temperature Stress Response and Fruit Development in Luffa

Plant-specific APETALA2/Ethylene-Responsive Factor (AP2/ERF) transcription factors are involved in the regulation of genes associated with the growth and developmental processes of numerous plants. Although AP2/ERF proteins from other species have been intensively studied, no studies have been reported on the AP2/ERF family of Luffa cylindrica, an important vegetable of the cucurbit family, and one of the most popular vegetables in the world. In this study, 133 genes (315–6696 bp) encoding LcAP2/ERF proteins with complete AP2/ERF domains were identified according to the luffa P93075 genome. These LcAP2/ERF genes were subsequently classified and analyzed for their gene structures, chromosomal distribution locations, promoter cis-acting elements, conserved structural domains of encoded proteins, and responses to abiotic stresses. The LcAP2/ERF genes were identified and divided into five phylogenetic groups (AP2, DREBs, ERFs, RAV, and soloists). These genes were unevenly distributed across 13 chromosomes. An analysis of gene structures indicated the LcAP2/ERF genes contained 0–11 introns (average of 4.4). Additionally, 16 motifs were identified in the LcAP2/ERF proteins that were conserved across different phylogenetic groups. Moreover, 11 cis-acting elements associated with response to the environment were analyzed in a 2000 bp region upstream of the LcAP2/ERF gene promoters. A transcriptome analysis involving RNA-seq data revealed tissue-specific LcAP2/ERF expression profiles and the diversity in LcAP2/ERF expression. The effects of low-temperature stress on LcAP2/ERF expression were determined. Furthermore, fruit-development-related and low-temperature-induced expressional changes were verified by RT-qPCR analyses of 14 differentially expressed LcAP2/ERF genes in luffa. Our findings will help clarify the evolution of the luffa AP2/ERF family, while also providing valuable insights for future studies on AP2/ERF functions.