Volatile Compounds from <i>Vishniacozyma victoriae</i> Induce Glandular Trichome Development in <i>Humulus lupulus</i>

H. lupulus (hops) is an essential ingredient in beer brewing owing to specialized metabolites stored in glandular trichomes (GTs) within cones. While metabolic pathways in GTs have been partially elucidated, the factors that trigger the GT formation remain unclear. Here, we found that volatile compounds produced by the phyllosphere yeast Vishniacozyma victoriae (V. victoriae) induced GT formation. We also identified 2-nonanone, a methyl ketone, as the bioactive compound in the volatiles released from V. victoriae that induced GT formation. Gene expression analyses revealed that treatment with volatile compounds produced by V. victoriae activated the expression of iron uptake-related genes in plants, indicating the involvement of iron uptake pathways in volatile-induced formation of glandular and non-glandular trichomes. Furthermore, exogenous treatment with 2-nonanone increased the GT density in multiple medicinal plants. These findings indicate that volatile compounds from V. victoriaea could serve as agricultural tools for GT induction in plants.