An ABA-inducible gene IbTSJT1 positively regulates drought tolerance in transgenic sweetpotato

The TSJT1 protein belongs to the superfamily of class-II glutamine amidotransferases (GATase). There is little research on the functions and underlying mechanisms of TSJT1 in plants. In this study, an abscisic acid (ABA)-inducible gene IbTSJT1 was isolated from drought-tolerant sweetpotato line ‘Xushu55-2’. Its expression was strongly induced by PEG6000 and ABA. The IbTSJT1 protein was localized in the nucleus and cell membrane. The IbTSJT1-overexpressing sweetpotato plants exhibited significantly enhanced drought tolerance. Their ABA and proline contents and superoxide dismutase (SOD) and peroxidase (POD) activities were increased and reactive oxygen species (ROS) scavenging-related genes were upregulated under drought stress. The stomatal aperture assay confirmed that the IbTSJT1-overexpressing plants increased the sensitivity to ABA. Yeast one-hybrid (Y1H) assay, electrophoretic mobility shift assay (EMSA), luciferase reporter assay and ChIP-qPCR assay indicated that IbABF2 could directly bind to the cis-acting ABA-responsive element (ABRE) in the IbTSJT1 promoter to activate the expression of IbTSJT1. These findings suggest that IbTSJT1 mediates ABA-dependent drought stress responses and enhances drought tolerance by inducing stomatal closure and activating ROS scavenging system in transgenic sweetpotato. Our study provides a novel gene for improving drought tolerance of sweetpotato and other plants.