Comparative analysis of NAC genes and their expression patterns under various treatments in Dendrobium huoshanense.

Extreme environmental conditions have significantly affected the natural habitats of Dendrobium huoshanense, a valuable medicinal orchid highly sensitive to abiotic stress. NAC transcription factors are key plants regulators, contributing to growth, development, and responses to environmental stresses. Despite their importance, information on the NAC gene family in D. huoshanense remains limited. In this study, a genome-wide analysis was conducted to identify and characterize D. huoshanense NAC genes, using integrated bioinformatics, phylogenetic, and expression profiles. A total of 77 DhNAC genes were identified, unevenly distributed across 19 chromosomes, with chromosome 4 containing the highest number of 16 genes. Phylogenetic and structural analysis grouped the DhNAC genes into 20 groups, with conserved NAM domains and diverse exon-intron structures, indicating both evolutionary conservation and functional specialization. Promoter region analysis identified the presence of diverse stress-responsive cis-regulatory elements, such as drought, cold, abscisic acid, methyl jasmonate, and salicylic acid signaling pathways, indicating their roles in stress adaptation. Comparative genomic studies with Arabidopsis thaliana, Dendrobium nobile, Oryza sativa, and Zea mays highlighted evolutionary relationships and revealed significant gene duplication, including tandem and segmental events. Finally, expression analysis of selected DhNAC gene using qRT-PCR showed differential expression under cold stress, methyl jasmonate, abscisic acid, and salicylic acid treatment. Under stress treatments, DhNAC genes showed distinct temporal expression patterns, with ABA inducing early, intermediate, and late responders, MeJA driving strong early-to-mid responses, and SA promoting sustained late responses. Key genes including DhNAC9, DhNAC19, DhNAC48, DhNAC51, DhNAC53, DhNAC55, DhNAC58, and DhNAC73 were consistently responsive, highlighting their central roles in stress adaptation. These findings provide valuable insights into the role of NAC genes in D. huoshanense in response to environmental stresses.