Strategies to Improve γ-Aminobutyric Acid Biosynthesis in Rice via Optimal Conditions

The γ-aminobutyric acid (GABA), a ubiquitous non-protein amino acid in plants and animals, exhibits diverse biological activities and holds promise in human disease prevention and treatment. Prior studies have shown that germination could substantially elevate GABA levels in rice, but these investigations typically focused on limited germplasms, hindering the generalization of their findings. This study aims to identify optimal conditions for enriching GABA in a diverse set of 225 rice germplasms by examining the effects of various germination times, temperatures, and soaking solution pH levels, while elucidating the key factors influencing GABA enrichment in germinated brown rice. The optimal GABA enrichment in germinated brown rice was achieved under the following conditions: a germination temperature of 37 °C, a germination duration of 48 h, and a soaking solution pH of 5.5. Under these conditions, we found significant differences in GABA content among different germplasms. Subsequent correlation analyses demonstrated that GABA content showed significant positive correlations with embryo weight in brown rice, relative embryo weight, relative embryo weight in germinated brown rice, as well as glutamate (Glu) and proline (Pro) concentrations. Therefore, larger brown rice embryos, higher Glu and Pro content in germinated brown rice, and external Glu application contribute to increased GABA content. Our findings provide essential materials and theoretical insights for screening and developing GABA-rich functional rice germplasms, facilitating variety selection and breeding programs.