PmbHLH58 from Pinus massoniana Improves Drought Tolerance by Reducing Stomatal Aperture and Inducing ABA Receptor Family Genes in Transgenic Poplar Plants

The basic helix-loop-helix (bHLH) family members are involved in plant growth and development, physiological metabolism, and various stress response processes. <i>Pinus massoniana</i> is a major turpentine-producing and wood-producing tree in seasonally dry areas of southern China. Its economic and ecological values are well known. The forestry industry holds it in exceptionally high regard. Drought severely limits the growth and productivity of <i>P. massoniana</i>, and the functional role of <i>PmbHLH58</i> in drought stress is not clear. Therefore, <i>PmbHLH58</i> was cloned from <i>P. massoniana</i> and its bioinformation was analyzed. Subcellular mapping of the gene was performed. The biological function of <i>PmbHLH58</i> overexpression in <i>Populus davidiana</i> × <i>P. bolleana</i> was studied. The results show that the drought tolerance of <i>PmbHLH58</i>-overexpressed poplar was significantly improved, which may be due to the increase in water use efficiency and reactive oxygen species (ROS) accumulation under drought stress. In an ethylene-responsive manner, PmERF71 interacted with the PmbHLH58 protein, which was found by yeast two-hybridization. We further demonstrated that the drought-induced <i>PmbHLH58</i> transcription factor increased the expression of key enzyme genes in ABA receptor family genes in <i>PmbHLH58</i>-overexpressing poplar lines (OE). These findings provide new insights into transcriptional regulation mechanisms related to drought stress and will promote the progression of the genetic improvement and plantation development of <i>P. massonsiana</i>.