Cloning of the <italic>NtCEP7</italic> gene in tobacco and functional analysis of its encoded peptide in seedling-stage drought resistance

Although tobacco exhibits strong drought tolerance at maturity, its seedlings are particularly sensitive to water deficiency during early developmental stages. Drought stress following field transplantation significantly disrupts plant growth, ultimately reducing yield and compromising leaf quality. C-terminally encoded peptides (CEPs), a class of small peptide hormones, are known to play crucial roles in regulating plant responses to abiotic stresses. However, the drought resistance functions of CEP family members in tobacco remain largely unexplored. In this study, we cloned the NtCEP7 gene from Nicotiana tabacum cv. K326. The full-length coding sequence (CDS) of NtCEP7 is 261 bp, encoding a protein of 86 amino acids. The predicted propeptide contains a typical secretory signal peptide and a transmembrane domain. Phylogenetic analysis placed NtCEP7 in Group I, and promoter analysis revealed the presence of cis-acting elements responsive to abscisic acid (ABA) and drought stress. Quantitative real-time PCR showed that NtCEP7 expression was significantly upregulated by both drought stress and ABA treatment. To assess its function, drought stress was simulated by withholding water from potted plants. Compared to the control group (sprayed with water), plants treated with NtCEP7a maintained a better growth status under drought conditions, which was manifested by milder leaf yellowing and wilting, exhibited increased chlorophyll content, net photosynthetic rate, dry weight of shoot and proline accumulation, along with decreased electrolyte leakage and malondialdehyde (MDA) levels. Further physiological analysis revealed that NtCEP7a treatment under drought conditions reduced stomatal aperture, increased relative leaf water content, enhanced antioxidant enzyme activities, and lowered levels of superoxide anions and hydrogen peroxide. Collectively, these results indicate that NtCEP7a alleviates drought-induced damage in tobacco by regulating stomatal dynamics, promoting osmoprotectant accumulation, and activating antioxidant defenses, thereby enhancing drought tolerance.