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

The consequences of climate change threaten the long-term sustainability of forests in Central Europe. In particular, extended drought periods are increasingly impacting the growth and survival of forest trees, underscoring the need for innovative approaches to adapt trees to drought. A deeper understanding of the functions of genes involved in drought tolerance can contribute to the development of effective strategies to address drought-related challenges. The homeobox-leucine zipper protein HDG11 has been identified as a promising target for enhancing drought stress tolerance in plants; however, the functional role of the native HDG11 gene in tree species remains uncharacterized. To address this, we identified the homolog of the AtHDG11 gene in the poplar hybrid Populus tremula x Populus alba and subsequently transformed the PtaHDG11 gene into the poplar hybrid clone INRA 717-1B4 for constitutive overexpression. Drought stress experiments revealed significantly enhanced drought stress tolerance in PtaHDG11-overexpressing poplars compared to the wildtype. This improved tolerance was characterized by reduced proline and malondialdehyde accumulation, increased relative leaf water content, decreased leaf shedding rates, and elevated expression of antioxidant-related genes, including SOD and CAT. Increased tolerance resulted in significantly increased dry biomass after the recovery phase. Notably, the PtaHDG11-overexpressing poplars presented a glabrous phenotype and lacked trichomes. Our study demonstrated the potential of PtaHDG11 to increase drought stress tolerance in trees by enhancing ROS detoxification and improving leaf water retention. These findings suggest that HDG11 is a promising candidate for improving drought resilience in trees, with implications for sustainable forest management and breeding programs. Main ConclusionPtaHDG11 overexpression enhanced drought tolerance in a transgenic poplar hybrid by attenuating the stress response, characterized by increased leaf RWC, increased expression of antioxidant genes, and reduced oxidative damage.