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.

Insights into dynamic regulatory factors in various stages of growth and development can guide strategies for precision and targeted breeding. Bitter gourd, as a vegetable product with medicinal value, plays a role in both agricultural and medical fields. In this study, phenotypic observations, metabolomic and transcriptomic analyses, and differential gene expression patterns, along with a correlation analysis, were conducted in different stages of fruit growth and development. The results revealed that the growth rate of fruit’s fresh weight, length, diameter, and flesh thickness during the first seven days was slow, and that it then rapidly increased after the seventh day, and finally slowed once more after 17 days, indicating that the overall process followed a “slow–fast–slow” pattern. Transcriptomic and metabolomic analyses identified several differentially expressed genes and metabolites, and joint analyses revealed that each of the glycolysis/gluconeogenesis, fructose and mannose metabolism and flavonoid biosynthesis pathways individually play significant roles in the dynamic regulation of fruit growth and development during the early, middle, and late stages. Among these, 53 differentially expressed genes (DEGs) and 12 differentially expressed metabolites (DEMs) were found in these pathways. A total of 12 randomly selected DEGs were analyzed using quantitative PCR, and the results showed that gene expression levels were generally consistent with transcriptomic sequencing results, exhibiting dynamic changes with varying expression levels. Correlation analysis revealed that 11 DEMs were positively correlated with four traits except for arbutin, while eight DEGs were related to all traits, including six significantly positive and two significantly negative correlations. These findings enhance our understanding of the regulatory network governing yield and quality and provide substantial evidence to support improvements in breeding programs.

Fruit flesh thickness is one of the key factors affecting the yield and quality of bitter melon, and its regulatory mechanisms remain unclear. One thick-flesh germplasm (KF) and one thin-flesh germplasm (NF) with significantly different flesh thicknesses were screened from 70 bitter melon germplasms. Through phenotypic surveys, combined metabolomic and transcriptomic analyses, and exogenous sugar treatments, the regulatory mechanisms on flesh thickness were preliminary investigated. The results showed that flesh thickness of the two germplasms remained stable during different years and seasons. Metabolomic and transcriptomic analyses revealed that fructose and mannose metabolism pathway significantly enriched in both omics datasets. The expression of key enzyme encoding genes from this pathway exhibited various expression patterns. In KF, most genes showed significantly higher expression levels than NF, with synergistic expression predominating among genes. Soluble sugar content was positively correlated with gene expression, while HXK, SDH, and TPI activities were negatively correlated with most genes, and FBP activity was positively correlated with most genes. Genes affect carbon source metabolic flux distribution by promoting sugar synthesis and inhibiting sugar respiration consumption. Exogenous sugar treatment exhibited germplasm-specific and concentration-dependent influence of gene expression, with KF primarily showing negative feedback and NF predominantly activating expression. Fruit flesh thickness was significantly positively correlated with the synergistic high expression of sugar metabolism genes and soluble sugar accumulation. This study provides a theoretical basis for molecular improvement of bitter melon fruit flesh thickness.

Herbivore-induced plant volatiles (HIPVs) are well recognized for their ability to recruit natural enemies of insect herbivores; however, their function in priming plant anti-herbivore defenses remains poorly elucidated. Here, we demonstrate that volatile exposure to a commercial β-ocimene isomer mixture (hereinafter referred to as β-ocimene) enhances anti-herbivore defense responses in tomato (Solanum lycopersicum) against the polyphagous lepidopteran pest Spodoptera litura (Fabricius). Larval infestation by S. litura significantly upregulated the expression of ten terpene synthase (TPS) genes that govern the biosynthesis of four dominant monoterpene HIPVs: β-ocimene, (-)-α-phellandrene, myrcene, and limonene. Preliminary bioassays revealed that pre-exposure to these four monoterpenes significantly enhances tomato resistance to S. litura larvae, with β-ocimene exhibiting the most pronounced effect. A 24 h pre-exposure to β-ocimene substantially augmented tomato antiherbivore resistance, and this protective response persisted for up to 10 days. Biochemical and molecular analyses revealed that pre-exposure to β-ocimene elevated the endogenous accumulation of jasmonic acid (JA) and jasmonoyl-isoleucine, along with increased transcript levels of the JA biosynthetic genes LOXD and AOS. Consistently, the JA biosynthesis-deficient mutant spr8 failed to exhibit strengthened antiherbivore resistance upon β-ocimene pre-exposure. Collectively, our results demonstrate that β-ocimene pre-exposure enhances tomato antiherbivore resistance via activating JA biosynthesis, highlighting the potential ecological function of HIPVs in priming plant defense against insect pests.