Secretory peptide PdEPF2 enhances drought tolerance by modulating stomatal density and regulates ABA response in transgenic Arabidopsis thaliana

Water deficit limits the growth and productivity of plants worldwide. Improved water use efficiency (WUE) and drought tolerance are important adaptations to address these limitations. In this study, an epidermal patterning factor (EPF), PdEPF2, from a fast-growing poplar clone NE-19 (Populus nigra × (Populus deltoids × Populus nigra)) was isolated. Quantitative reverse transcription polymerase chain reaction showed that transcription of this gene was induced by drought and abscisic acid (ABA). To study the biological functions of PdEPF2, transgenic Arabidopsis plants harboring (35S:PdEPF2) in which PdEPF2 was constitutively expressed were generated. Compared with the wild type and epf2-3 mutant, the transgenic plants ectopically expressing PdEPF2 showed favorable osmotic parameters, such as seed germination rate, primary root length, proline and chlorophyll content, Fv/Fm, photosynthetic rate, and instantaneous leaf WUE, under drought stress. In addition, the transgenic Arabidopsis plants displayed enhanced drought tolerance as a result of decreased stomatal density, which would limit transpiration and reduce water loss. Compared with the wild-type, plants that overexpressed PdEPF2 had decreased sensitivity to exogenous ABA during germination and seedling development, whereas the epf2-3 mutant showed increased sensitivity to ABA. Furthermore, PdEPF2 positively regulated expression of two ABA signaling-related genes, ABI1 and ABI2. These findings indicate that PdEPF2 may enhance drought tolerance by regulating stomatal density and the response to the ABA signaling pathway.