Abstract
BACKGROUND: The HD-Zip family of plant-specific transcription factors coordinates developmental processes and abiotic stress adaptation, including drought tolerance in bioenergy crops such as physic nut. Although HD-Zip proteins are known regulators of stress responses, the functional roles of physic nut HD-Zip genes in drought adaptation remain uncharacterized. RESULTS: In this study, we functionally characterized JcHDZ25, a drought-inducible HD-Zip I gene from physic nut, which is predominantly expressed in roots and upregulated by ABA and drought. Subcellular localization and transcriptional activity assays confirmed that JcHDZ25 localized to the nucleus and exhibited intrinsic transcriptional activation. Transgenic rice overexpressing JcHDZ25 displayed enhanced drought tolerance and ABA sensitivity compared to wild-type plants. Under drought stress, JcHDZ25-overexpressing lines showed significantly higher proline content, elevated SOD and CAT activities, and reduced electrolyte leakage and MDA accumulation relative to wild-type controls. Furthermore, transgenic plants showed higher expression of abiotic stress-responsive genes (OsAPX2, OsCATA, OsLEA3, OsP5 CS, OsDREB2 A, OsADC1) and ABA pathway-related genes (OsNCED3, OsRD29 A) under drought stress compared to wild-type plants. CONCLUSIONS: JcHDZ25 positively regulates drought tolerance in rice possibly through an ABA-dependent transcriptional regulation, providing mechanistic insights into physic nut's drought adaptation and highlighting its potential as a genetic resource for engineering stress-resilient crops.