Crosstalk Between the SlNAC48/SlNAC89– SlXTH23 Module and ABA Signalling Enhances Drought Tolerance in Tomato by Regulating Stomatal Closure

Drought is a major environmental constraint on crop growth, development, and yield. Xyloglucan endotransglucosylase/hydrolases (XTHs) have been reported to play important roles in plant drought tolerance. We previously identified the cold-responsive tomato gene SlXTH23 as a positive regulator of cold tolerance; however, its function and underlying mechanism in drought tolerance remain unclear. Here, drought stress suppressed SlXTH23 expression. Drought tolerance was reduced in SlXTH23-overexpression lines but enhanced in SlXTH23-knockout lines. Under drought stress, stomatal aperture increased in the overexpression lines. Protein-DNA interaction assays demonstrated that the transcription factors SlNAC48 and SlNAC89 bind directly to the SlXTH23 promoter and repress its transcription. Silencing SlNAC48 or SlNAC89 reduced SlNCED3 expression and abscisic acid (ABA) content but increased stomatal aperture under drought stress. Moreover, ABA deficiency reduced tomato drought tolerance and increased both stomatal aperture and SlXTH23 expression. Collectively, drought stress induces SlNAC48 and SlNAC89, which repress SlXTH23 transcription and thereby restrict stomatal aperture. The SlNAC48/SlNAC89-SlXTH23 module also interacts with ABA signalling, and ABA may act synergistically with this module to enhance drought tolerance in tomato seedlings.