The Bitter Gourd Transcription Factor McNAC087 Confers Cold Resistance in Transgenic Arabidopsis

Low-temperature stress severely restricts the growth, development, and yield of bitter gourd (Momordica charantia L.), a warm-loving crop with inherent low cold tolerance. NAC transcription factors (TFs) serve as crucial regulators in plant responses to abiotic stresses like cold, while their roles in coping with cold stress in bitter gourd remain unclear. This study identified cold-responsive genes in bitter gourd and characterized the candidate NAC TF McNAC087 through transcriptome analysis. Transcriptome sequencing of cold-tolerant (R) and cold-sensitive (S) bitter gourd inbred lines under 5 °C stress (0 h, 6 h, 12 h, 24 h) revealed 1157 co-expressed differentially expressed genes (DEGs), enriched via Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis in cold tolerance-related pathways (signal transduction, carbohydrate/amino acid metabolism). RT-qPCR showed higher McNAC087 expression in R than S under cold stress, and subcellular localization confirmed it as a nucleus-localized protein. McNAC087 overexpression in Arabidopsis enhanced cold tolerance after sequential stress (-14 °C for 1.5 h, 4 °C for 16 h, and 22 °C recovery for 2 days), with less damage compared to wildtype (WT). Physiologically, overexpressing lines had higher proline, elevated superoxide dismutase/peroxidase/catalase (SOD/POD/CAT) activities, lower malondialdehyde/hydrogen peroxide/superoxide anion (MDA/H₂O₂/O₂^-) accumulation under cold stress, and upregulated ICE-CBF-COR pathway marker genes (CBF1, DREB2A, RD29A, COR47). In conclusion, McNAC087 enhances Arabidopsis cold tolerance by regulating physiology and activating cold-responsive genes, providing insights for bitter gourd cold tolerance mechanisms and crop breeding.