PagE2Fa1 negatively regulates drought tolerance in poplar by modulating root development and stomatal aperture

E2F/DP proteins play a critical role in plant growth by regulating the cell cycle, yet the function of E2F/DP proteins in stress responses of woody plants is poorly understood. Here, nine PagE2F/DP members were identified in 84K poplar (Populus alba × P. glandulosa), and we selected PagE2Fa1, which was highly expressed in roots and in response to drought, for functional investigation. Transgenic poplar overexpressing PagE2Fa1 (PagE2Fa1 OE) showed no obvious aboveground phenotypic differences compared with non-transgenic 84K poplar, but root growth was significantly inhibited. Following 15 days of drought treatment, PagE2Fa1 OE displayed substantially reduced plant height and aboveground biomass, along with demonstrating drought intolerance. Further analyses revealed that leaves of PagE2Fa1 OE had higher water loss rates and accumulated more reactive oxygen species after drought treatment. Moreover, the activities and transcript levels of antioxidant enzymes (SOD, CAT, APX) were significantly downregulated in PagE2Fa1 OE transgenic lines. Overall, our findings reveal that PagE2Fa1 negatively regulates drought tolerance by restricting root development, increasing stomatal aperture and suppressing the expression of antioxidant genes. This study reveals the function of PagE2Fa1 in drought response, identifying it as a promising genetic target for enhancing drought tolerance in forest trees.