Gene expression analysis of a giant embryo rice mutant with high GABA content

Gamma-amino butyric acid (GABA) is a natural non-protein amino acid involved in plant stress, signal transmission, carbon and nitrogen balance, and other physiological effects in plants. In the human body, it has the effects of lowering blood pressure, anti-aging, and activating the liver and kidney. However, there are few studies on the molecular regulation mechanism of genes in the metabolic pathways of GABA during grain development of giant embryo rice with high GABA content. In this study, three glant embryo (ge) mutants of different embryo sizes were obtained by CRISPR/Cas9 knockout, and it was found that GABA, protein, crude fat, and various mineral contents of the ge mutants were significantly increased. RNA-seq and qRT-PCR analysis showed that in the GABA shunt and polyamine degradation pathway, the expression levels of most of genes encoding enzymes promoting GABA accumulation were significantly upregulated in the ge-1 mutant, while the expression levels of most of genes encoding enzymes conducive to GABA degradation were significantly downregulated in the ge-1 mutant. This is most likely responsible for the significant increase in GABA content of the ge mutant. These results are helpful in revealing the molecular regulatory network of GABA metabolism in giant embryo rice and provide a theoretical basis for the study of its development mechanisms, which is conducive to the rapid cultivation of GABA-rich rice varieties, promoting human nutrition, and ensuring health.