Overexpression of PtaHDG11 enhances drought tolerance and suppresses trichome formation in Populus tremula x Populus alba

Extended drought periods are increasingly impacting the growth and survival of forest trees in Central Europe, underscoring the need for innovative approaches to adapt trees to drought. Understanding the functions of genes involved in drought tolerance can contribute to the development of effective strategies to improve drought resilience. Although the homeobox-leucine zipper protein HDG11 has been identified as a promising target for enhancing drought stress tolerance in plants, the functional role of the native HDG11 gene in tree species remained uncharacterized. To address this gap, we identified the homolog of the AtHDG11 gene in the poplar hybrid Populus tremula x Populus alba, clone INRA 717-1B4, and subsequently transformed the PtaHDG11 gene into this clone for constitutive overexpression. Drought stress experiments revealed significantly enhanced drought stress tolerance in PtaHDG11-overexpressing poplars compared with the wild type. This improved tolerance was characterized by higher leaf relative water content, reduced leaf shedding, lower malondialdehyde accumulation and higher expression of antioxidant-related genes, including SOD and CAT. Improved tolerance resulted in significantly increased dry biomass after the recovery phase. Notably, the transgenic poplars exhibited altered basal expression of the cell wall-related genes PtaXTH32-like and PtaEXPA15-like under control conditions, indicating a modified cell wall-associated regulatory state before stress exposure. In addition, PtaHDG11 overexpression was associated with a glabrous phenotype lacking trichomes, pointing to functions of PtaHDG11 beyond drought stress responses in a woody perennial. Together, these findings suggest that PtaHDG11 can contribute to improving drought resilience in trees, with implications for sustainable forest management and breeding programs.