Differential effects of Catharanthus roseus-mediated selenium nanoparticles and GABA on terpenoid indole alkaloid biosynthesis and gene expression in Catharanthus roseus

Background Catharanthus roseus is considered the primary plant source of terpenoid indole alkaloids (TIAs) including vinblastine and vincristine, whose low natural abundance motivates strategies to enhance their biosynthesis. This study evaluated the effect of biogenic selenium nanoparticles (SeNPs) synthesized using C. roseus leaf extract and γ-aminobutyric acid (GABA) as foliar elicitors of TIA production and the expression of their key biosynthetic genes. Methods SeNPs were prepared from C. roseus extract and sodium selenite and characterized by UV–Vis, X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Dynamic Light Scattering (DLS)/zeta, Transmission Electron Microscopy (TEM), and Energy-Dispersive X-ray Spectroscopy (EDX). The experiment was conducted across eight treatments, with three replicates for each (three pots, two plants per pot), in a 4 × 2 completely randomized factorial design. Foliar treatments (SeNPs; 0, 10, 30, and 50 ppm, in the presence or absence of 0.5 mM GABA) were applied three times at two-week intervals; biochemical and molecular analyses were performed on 70-day-old leaves. Results SeNP formation was preliminarily indicated by the color change from yellow to dark red and was characterized by broad UV–Vis absorbance, and XRD analysis revealed a mixed monoclinic and amorphous mixed structure of the selenium nanoparticles. FTIR revealed the role of secondary metabolites in stabilizing and capping selenium nanoparticles. While TEM revealed the semi-spherical core, EDX confirmed selenium and organic capping elements. Each treatment exhibited a distinct metabolite accumulation and gene expression modulation; individual treatment with GABA caused the highest accumulation of catharanthine and vincristine, while treatment with 30 ppm SeNPs caused the highest accumulation of vindoline and vinblastine. In the combined treatments, only the treatment with 10 ppm SeNPs and GABA succeeded in accumulating the highest vindoline concentration. All treatments modulated the transcription of deacetylvindoline 4-O-acetyltransferase (DAT) and desacetoxyvindoline 4-hydroxylase (D4H) differentially. The results showed treatment-dependent, concentration-specific redirection of metabolite accumulation pattern and transcriptional modulation. Conclusions Biogenic SeNPs synthesized with C. roseus extract, and GABA, elevated expression of TIA pathway genes and selectively enhanced accumulation of key alkaloids (vinblastine, vincristine, vindoline, catharanthine) in a concentration-dependent manner. Optimization of SeNP formulation and application regime could provide a promising laboratory-scale strategy for enhancing alkaloid accumulation in C. roseus .