Biological function analysis of stress response factor <italic>NcMYC2</italic> gene in <italic>Neolamarckia cadamba</italic>

Neolamarckia cadamba is an evergreen fast-growing tree rich in medicinally active ingredients, which is widely used in traditional medicine, timber production and afforestation. MYC transcription factors, belonging to the bHLH transcription factor family, play significant roles in plant stress responses, hormone signaling transduction, and the regulation of plant secondary metabolite biosynthesis. In order to explore the function of NcMYC2 in N. cadamba, the study cloned the NcMYC2 gene, analyzed its expression patterns under different physiological ages, abiotic stresses and hormone treatments and preliminarily explored its biological role. The results showed that the full-length cDNA sequence of NcMYC2 was 2 297 bp, containing an open reading frame (ORF) of 1 578 bp that encodes 526 amino acids. This gene contains two conserved domains, bHLH_AtAIB_like and bHLH-MYC_N, and shares the closest phylogenetic relationship with HbMYC2 of Hevea brasiliensis. The NcMYC2 protein was localized in the nucleus and exhibited transcriptional activity in yeast. The NcMYC2 promoter contained multiple cis-acting elements involved in light, hormonal, and stress responses. The results of expression analysis revealed that NcMYC2 was expressed in all organs across different developmental stages, with the highest transcript level in leaves. Under 1 mmol·L−1 methyl jasmonate (MeJA) treatment, NcMYC2 expression was predominantly induced in leaves and peaked at 24 h. Treatment with 10 mg·L−1 abscisic acid (ABA) promoted the expression of NcMYC2 in leaves, whereas 100 mg·L−1 ABA suppressed it. Under 100 mmol·L−1 NaCl salt stress, NcMYC2 responded mainly in roots, exhibiting an expression pattern that initially increased and then decreased overexpression of NcMYC2 in Arabidopsis thaliana significantly improved seed germination rates under salt stress and enhanced the salt tolerance of seedlings. These results demonstrated that NcMYC2 played a crucial role in the salt stress response of N. cadamba.