Gamma-ray sensitivity and gene expression responses to methyl jasmonate treatment for the radiation breeding of the Hyangcho and KB113LC tobacco cultivars (Nicotiana tabacum L.) at different stages

Gamma-ray mutagenesis is a widely used technique in plant breeding, but its efficiency depends on the developmental stage, genotype, and timing of irradiation after pretreatment. The aim of this study was to determine the radiosensitivity of two Korean tobacco cultivars, Hyangcho and KB113LC, across developmental stages and to explore whether methyl jasmonate (MeJA) treatment can modulate the expression of target gene sets to enhance mutation induction. Tobacco seeds (ranging from 0 to 1000 with 100 Gy steps) and plants at the vegetative and reproductive stages (ranging from 0 to 200 with 25 Gy steps) were irradiated with γ-rays, and growth parameter data were collected to determine 50% reduction dose (RD50) values. The non-irradiated control plants at vegetative and reproductive stages were treated with 500 µM MeJA by foliar spraying, and temporal expression of MeJA-responsive and nicotine biosynthesis-related genes was assessed using qRT-PCR over a 0–48 h period. The RD50 mean values of each parameter varied by cultivar and stage, with Hyangcho (mean 66 Gy) showing greater radiosensitivity than KB113LC (mean 79 Gy) at both the vegetative and reproductive stages but greater resistance at the seed stage (mean 405 vs. 312 Gy, Hyangcho vs. KB113LC). MeJA treatment induced no obvious physiological alterations; however, the expression of early-response genes (e.g., NtJAZ1, NtMYC2a) peaked at 0.5–1 h post-MeJA treatment, while late-response genes (e.g., NtERF189, NtQPT2) peaked at 16–32 h, with NtODC showing particularly strong activation in KB113LC. The study findings support the introduction of a practical framework for stage- and genotype-specific γ-ray mutagenesis in tobacco, guided by the timing of MeJA-responsive gene activations. Based on the literature, MeJA pretreatment is assumed to potentially increase mutagenesis efficiency; our data define optimal conditions for testing this hypothesis, supporting the development of tobacco mutant populations, including low-nicotine tobacco lines aligned with evolving public health guidelines.