Construction of a high-density genetic map, QTL detection, and functional validation of the major regulator Ovh1HD1 for glandular secretory trichome density in oregano

The genus Origanum comprises important aromatic and medicinal plants. Oregano essential oil, which contains bioactive components, has emerged as one of the most promising alternatives to antibiotics in the livestock industry. These components are produced by glandular secretory trichomes (GSTs). Therefore, increasing GST density is a key approach in molecular breeding to enhance essential oil yield. In this study, we developed an F 2 breeding population of 232 individuals derived from a cross between O. vulgare ‘Hot & Spicy’ (high GST density) and O. vulgare (low GST density). The GST densities on the leaf adaxial surface (GADS), abaxial surface (GABS), and total surfaces (GSTS) in the F 2 population showed significant variation and exhibited obvious superparental dominance. The genetic linkage map comprised 15 linkage groups (LGs) and spanned 2,279.28 centimorgans (cM), with an average interval of 0.48 cM. In 2024, we identified 3, 11, and 5 QTLs associated with GADS, GABS, and GSTS, respectively. In 2025, we identified 4, 6, and 5 QTLs for the same traits, respectively. Finally, a HD-ZIP IV transcription factor, designated Ovh1HD1 , was identified within the GSTS-2024 QTLs. Overexpression in tobacco revealed that higher expression levels of this gene led to a corresponding increase in trichome density. Therefore, it is hypothesized that Ovh1HD1 indirectly promotes glandular trichome formation in tobacco by repressing NbCycB2 , which in turn leads to the upregulation of Nbwolly .