The basic helix-loop-helix (bHLH) family of transcription factors (TFs) plays a critical role in regulating plant resistance to various abiotic stresses, including drought, low temperature, high salinity, and iron deficiency, as well as in overseeing key processes in plant growth and development. Despite the well-documented functions of bHLH TFs in many plant species, their roles in Populus davidiana × P. bolleana under abiotic stress conditions remain largely unexplored. This study identified a bHLH gene, designated as PdbbHLH1, whose expression is markedly upregulated in response to PEG₆₀₀₀ treatment. To investigate its function, the research generated transgenic Populus plants overexpressing (OE) PdbbHLH1 through Agrobacterium tumefaciens-mediated transformation. Stress experiments demonstrated that OE PdbbHLH1 significantly enhanced the drought resistance of these transgenic plants, as evidenced by increased fresh weight and chlorophyll content compared to wild-type (WT) plants under drought conditions. Physiological analyses further revealed that PdbbHLH1-OE plants exhibited lower levels of hydrogen peroxide (H₂O₂) and malondialdehyde (MDA), indicating reduced cellular damage and a more robust reactive oxygen species (ROS) scavenging capability than WT plants. Furthermore, the expression of drought resistance-related genes, such as PdbAAO, PdbGST, and PdbPOD, was significantly upregulated in OE plants post-drought stress. Notably, PdbbHLH1 was shown to directly bind to the promoters of PdbPOD1 and PdbPOD4, activating their expression and thereby enhancing the drought resistance of transgenic Populus davidiana × P. bolleana. Collectively, these results suggest that PdbbHLH1 is a key regulator of drought tolerance in Populus, modulating this response through the enhancement of antioxidant enzyme activities at the physiological level.

转录因子 (TF) 的基本螺旋-环-螺旋 (bHLH) 家族在调节植物对各种非生物胁迫（包括干旱、低温、高盐度和缺铁）的抗性以及监督关键过程方面发挥着关键作用在植物生长和发育中。尽管 bHLH TF 在许多植物物种中的功能已有充分记录，但它们在非生物胁迫条件下的山杨×波里纳中的作用仍然很大程度上未被探索。这项研究鉴定了一个 bHLH 基因，命名为PdbbHLH1 ，其表达在 PEG ₆₀₀₀处理后显着上调。为了研究其功能，该研究通过根癌农杆菌介导的转化产生了过表达（OE） PdbbHLH1的转基因杨树植物。胁迫实验表明，OE PdbbHLH1显着增强了这些转基因植物的抗旱性，与干旱条件下野生型 (WT) 植物相比，鲜重和叶绿素含量增加就证明了这一点。生理分析进一步表明， PdbbHLH1 -OE植物表现出较低水平的过氧化氢（H ₂ O ₂ ）和丙二醛（MDA），表明细胞损伤减少，并且比WT植物具有更强的活性氧（ROS）清除能力。此外，干旱胁迫后OE植物中抗旱相关基因的表达显着上调，例如PdbAAO 、 PdbGST和PdbPOD 。 值得注意的是， PdbbHLH1被证明可以直接结合PdbPOD1和PdbPOD4的启动子，激活它们的表达，从而增强转基因山杨×大花杨的抗旱性。总的来说，这些结果表明PdbbHLH1是杨树耐旱性的关键调节因子，通过在生理水平上增强抗氧化酶活性来调节这种反应.