Genome-Wide Identification and Expression Analysis of the Dirigent Gene Family in Dendrobium lindleyi

Dendrobium lindleyi is an orchid species valued for both ornamental and medicinal purposes; its secondary metabolites possess heat-clearing and fluid-generating properties. Dirigent (DIR) proteins play a key regulatory role in plant lignin polymerization and responses to abiotic and biotic stresses; however, systematic studies of DIR family genes in D. lindleyi are lacking. The objective of this study was to systematically characterize the DIR gene family in D. lindleyi. To achieve this, bioinformatics methods were used to identify DIR genes genome-wide, followed by analyses of their post-translational modifications, gene and protein structures, phylogeny, promoter cis-regulatory elements, expression patterns, and subcellular localization. The results show that 15 DIR family genes were identified in the D. lindleyi genome. The DIR family is divided into five subfamilies: DIR-a, DIR-b/d, DIR-c, DIR-e, and DIR-g, among which DIR-b/d has the most members (9), and DlDIR2 and DlDIR4 exhibit a fragment duplication event. The promoter regions are rich in light-responsive, ABA, MeJA, MYB, MYC, WRKY, and oxidative stress-related elements, suggesting that DIR genes in D. lindleyi may be involved in multiple signaling pathways. Transcriptomic and qRT-PCR analyses revealed that DlDIR8 exhibits a strong response to ABA treatment, with ABA inducing its downregulation. Subcellular localization studies revealed that the DlDIR8 protein is localized to the nucleus. These findings provide a foundation for the functional characterization of the DIR gene family in D. lindleyi and highlight DlDIR8 as a candidate in the ABA-mediated stress response, offering a theoretical basis for the potential genetic improvement of this species.