Response of the Larix olgensis NAC transcription factor LoNAC2 to drought stress

Larch is an important afforestation tree species in China, valued for their fast growth and high-quality timber. However, progress in traditional resistance breeding has been slow, making gene functional analysis and transgenic breeding research essential. NAC transcription factors play key roles in plant stress responses and growth development; however, functional studies on larch NAC genes remain limited. This study focused on the LoNAC2 gene from Larix olgensis. We constructed an overexpression vector to generate stable transgenic larch callus and tobacco lines, which were then used to investigate the responses of LoNAC2-overexpressing materials to drought stress. Under drought stress, LoNAC2 overexpression significantly increased callus fresh weight and growth rate, enhanced tobacco seed germination, seedling growth, and whole-plant survival rate, and maintained higher relative water content through stomatal regulation. Both callus and plant tissues exhibited significantly higher SOD and POD activities than wild-type controls. Histochemical staining revealed reduced H₂O₂ and O₂^- accumulation, indicating enhanced ROS-scavenging capacity. This enhanced antioxidant capacity maintained stable chlorophyll content and reduced malondialdehyde (MDA) accumulation. Transcriptome analysis showed significant upregulation of multiple key antioxidant and stress-response-related genes in transgenic plants, including NtSOD, NtPOD, Nt- GST, NtAPX, NtNCED1, and NtDREB1A. These genes synergistically promote stomatal closure via hormonal signaling pathways, such as abscisic acid (ABA), to reduce water loss, while simultaneously enhancing enzymatic and non-enzymatic antioxidant capacities to effectively scavenge reactive oxygen species and mitigate oxidative damage. In summary, this study reveals the important role of LoNAC2 in regulating stomatal function and antioxidant defense, providing a valuable candidate gene for molecular breeding of drought tolerance in larch and other coniferous species.