GABA is a key player regulating the TCA cycle and polyamine metabolism under combined heat-drought stress in tea plants

• Heat and drought combined stresses exacerbated the stress damage to tea plants. • Metabolic analysis showed that combined HS-DS led to metabolites accumulation related to TCA cycle. • The metabolites in arginine and proline metabolism pathway were significantly changed under HS-DS. • 4. Exogenous spraying showed that GABA played a crucial part in the resistance of tea plants to combined HS-DS. Throughout their development, plants experience a range of abiotic stresses, typically not solitary occurrences. For example, drought stress (DS) and heat stress (HS) often co-occur due to a high-temperature environment being accompanied by drought. Differing from single stress, plants have unique responses to the stress combination, with secondary metabolism holding a pivotal position in the process of plant response. Under combined stresses, plants specifically induce the accumulation of secondary metabolites to resist damage. We found that the metabolic responses of tea plants ( Camellia sinensis ) to DS or HS differed from those to a combination of HS and DS (HS-DS). Metabolic analysis showed that combined HS-DS led to the up-regulation and down-regulation of abundance of key metabolites in the tricarboxylic acid (TCA) cycle and polyamine metabolism pathways. Among the metabolites accumulated under combined HS-DS was γ-aminobutyric acid (GABA). Exogenous spraying of 1 mM GABA and silencing the GABA-synthesis-related gene [glutamate decarboxylase 1 ( GAD1 )] showed that GABA played a crucial part in the resistance of tea plants to combined HS-DS. This study reveals the function of GABA in regulating the response of tea plant to HS-DS, which provides a theoretical basis for the subsequent research on heat and drought resistance for plants.