Gamma-aminobutyric acid (
GABA) is a four-
carbon non-
protein amino acid conserved from bacteria to plants and vertebrates. Increasing evidence supports a regulatory role for
GABA in plant development and the plant's response to environmental stress. The biosynthesis of
nicotine, the main economically important metabolite in tobacco, is tightly regulated.
GABA has not hitherto been reported to function in
nicotine biosynthesis. Here we report that water flooding treatment (
hypoxia) markedly induced the accumulation of
GABA and stimulated
nicotine biosynthesis. Suppressing
GABA accumulation by treatment with
glutamate decarboxylase inhibitor impaired flooding-induced
nicotine biosynthesis, while exogenous
GABA application directly induced
nicotine biosynthesis. Based on these results, we propose that
GABA triggers
nicotine biosynthesis in tobacco seedlings subjected to flooding. Our results provide insight into the molecular mechanism of
nicotine biosynthesis in tobacco plants exposed to environmental stress.