Identification and expression of the Glycyrrhiza uralensis GABA shunt gene family under drought and salt stress with exogenous GABA.

Glycyrrhiza sp. (licorice) is a high-value medicinal plant, which is primarily distributed in drought and salt environments. However, wild licorice resources are dwindling, and salt and drought stresses reduce biomass, hampering the licorice industry. As a signalling molecule, γ-Aminobutyric acid (GABA) regulates tolerance to various abiotic stresses. Therefore, we studied biochemical indicators and GABA shunt gene expression in G. uralensis under abiotic stress. For the first time, six GABA shunt genes were identified in G. uralensis genome, including three GuGADs, one GuGABP, one GuGABA-T, and one GuSSADH. Their cis-acting elements were related to hormone and environmental responses, revealed that they played a role in G. uralensis growth and development. Under drought and salt stress and stresses combined with exogenous GABA, the genes of GuSSADH, GuGABP, and GuGADs were all significantly upregulated. Moreover, exogenous GABA could promote plant growth, regulate endogenous GABA levels and improve the activity of superoxide dismutase (SOD), catalase (CAT), malondialdehyde (MDA), and the content of soluble sugar and soluble protein. Our findings confirm that exogenous GABA alleviates the damage caused by salt and drought stress by simultaneously boosting the antioxidant system to combat oxidative damage and enhancing osmotic adjustment to maintain cellular water relations. The observed stress-intensity specific optimisation points are noteworthy for understanding how GABA and GABA shunt modulate these protective responses.