The HD-Zip II Transcription Factor SlHZ07 Promotes Growth and Drought Tolerance in Tomato.

Drought is one of the major environmental constraints limiting tomato growth and productivity. Identifying regulators that enhance drought tolerance without compromising plant growth is therefore important for tomato production. Homeodomain-leucine zipper (HD-Zip) transcription factors (TFs) play essential roles in plant development and abiotic stress responses; however, the functions of most HD-Zip II members in tomato remain poorly understood. Here, we identified SlHZ07, a drought-responsive HD-Zip II TF, through transcriptome analysis and characterized its biological function in tomato. SlHZ07 was rapidly induced by drought stress and localized predominantly to the nucleus. Overexpression of SlHZ07 significantly enhanced drought tolerance, whereas RNAi-mediated suppression increased drought sensitivity. Physiological analyses showed that SlHZ07 overexpression reduced reactive oxygen species (ROS) accumulation, enhanced antioxidant enzyme activities, upregulated expression of ROS-scavenging genes, and alleviated membrane damage under drought stress. Hormone analyses revealed that SlHZ07 positively regulated jasmonic acid (JA) accumulation and the expression of JA biosynthetic genes, including OPR2, OPR3, JAR1, and AOC, but did not alter endogenous abscisic acid (ABA) levels under well-watered conditions. Furthermore, SlHZ07 promoted vegetative growth by increasing endogenous gibberellin (GA) levels and upregulating the expression of the GA biosynthetic genes GA20ox2 and GA20ox4. Together, our findings identify SlHZ07 as a previously uncharacterized positive regulator that coordinates plant growth and drought adaptation by integrating GA biosynthesis, JA homeostasis, and ROS detoxification. These results expand our understanding of HD-Zip II TFs and provide a promising genetic target for improving drought tolerance in tomato.