Genome-Wide Identification and Characterization of the Dehydrin Gene Family in Sesame (Sesamum indicum): Structural Divergence and Differential Expression Under Drought Stress.

Background/Objectives: Dehydrins (DHNs) are late embryogenesis abundant proteins that play protective roles under water-deficit conditions; however, their organization and function remain unexplored in sesame (Sesamum indicum), an important oilseed crop frequently cultivated in arid and semi-arid regions. This study aimed to identify and characterize the DHN gene family in sesame and evaluate the expression of its members under drought stress. Methods: Genome-wide identification was performed using the Dehydrin domain HMM profile, followed by phylogenetic analysis, conserved motif and gene structure characterization, synteny analysis, promoter cis-element profiling, and secondary/tertiary structure prediction. Transcriptional responses were profiled by qPCR in two sesame cultivars (drought-sensitive and drought-tolerant) under PEG-induced osmotic stress at germination and seedling stages. Results: Four DHN genes were identified, spanning three phylogenetic subfamilies (I-III) and three DHN subclasses: SKn (SiDHN1/2), YnKn (SiDHN3), and YnSKn (SiDHN4). SiDHN1 and SiDHN2 likely arose from a segmental duplication, and a single conserved syntenic pair was found between SiDHN4 and olive (Olea europaea). Secondary structure predictions uncovered contrasting structural propensities: SiDHN1/2 are predicted to be α-helix-rich, partially ordered proteins (41-44% predicted α-helix), whereas SiDHN3/4 are predicted to be predominantly intrinsically disordered (~75-80% random coil). SiDHN3 was consistently upregulated across all conditions (1.84-9.12-fold), while SiDHN4 exhibited strong genotype-specific induction of 9.39-fold exclusively in the drought-tolerant cultivar during germination. Conclusions: The sesame DHN family achieves functional breadth through structural diversification-an ordered-disordered continuum mirrored by divergent expression programming-rather than through numerical expansion. SiDHN3 and SiDHN4 are identified as primary candidates for drought tolerance improvement in sesame.