Tomato SlERF26 enhances drought tolerance by regulating SlPIP2;4-mediated ROS homeostasis

Adverse environmental conditions severely limit plant growth and productivity, especially under an increasingly frequent and severe drought. Cultivated tomato is highly sensitive to drought, while wild tomato species exhibit remarkable drought tolerance. In this study, we identified SlERF26 as a drought-responsive gene that was differentially expressed between drought-tolerant Solanum pennellii introgression lines and the cultivated tomato background through combined introgression-line and transcriptomic analyses. SlERF26 encodes an AP2/ERF (APETALA2/Ethylene Response Factor) transcription factor. Under drought stress, overexpression of SlERF26 reduced the accumulation of reactive oxygen species (ROS), including H₂O₂ and O₂^-, which is consistent with its positive role in regulating drought tolerance. Transcriptome profiling further indicated that SlERF26 regulated a series of drought-responsive genes involved in membrane transport and ROS scavenging, such as aquaporin and peroxidases. Specifically, SlERF26 directly bound to the promoter of SlPIP2;4, an aquaporin gene, and activated its transcription. The slpip2;4 mutant accumulated higher ROS levels and exhibited significantly reduced drought tolerance. Moreover, analysis of SlERF26 OE × slpip2;4 hybrid plants confirms that SlERF26 acts upstream of SlPIP2;4 in drought tolerance. Consistent with this genetic relationship, biochemical quantification and histochemical staining demonstrated that SlERF26 and SlPIP2;4 act together to maintain ROS homeostasis during drought stress. Collectively, our findings define a SlERF26-SlPIP2;4 regulatory module that enhances drought tolerance in tomato by modulating aquaporin expression and ROS homeostasis.