Thyme is widely distributed in the worldwild. In China, there are 15 species, 2 varieties and 1 variant. Thymus quinquecostatus which contains abundant bioactive terpenoids is an important wild medicinal and aromatic plant in Chinese native thymes. Thymus vulgaris ‘Elsbeth’ comes from Europe and is known for its medicinal properties. The terpenoids exist in the glandular trichomes (GTs), a special epidemal structure. In Lamiaceae, glandular trichomes usually include peltate glandular trichomes (PGTs) and capitate glandular trichomes (CGTs). In previous study, we had analysed the molecular mechanisms of GTs but the formation process was not revealed. In this study, we observed the formation of PGTs and CGTs in thyme. The PGT underwent the complex process, including the basal, stalk, and head cells, there were 8-12 head cells. The CGT also had three cells, but its head cell only had one cell. Meanwhile, molecular biology research was carried out and we identified 68 HD-ZIP proteins and selected several key genes related to the formation of GTs according to the expression levels. Then, we cloned an HD-ZIP Ⅳ transcription factor TqHD1 from T. quinquecostatus and characterized it. TqHD1 not only can promote the formation of GTs but also can lead to the changes of volatile components and some relative genes levels. These findings complete the study of cell micromorphology of thyme and lay the foundation for characterization of factors in epidermis-related functions in thyme.

To protect themselves from herbivore attacks, especially during early developmental stages, plants produce volatiles possessing various ecological and physiological functions. Here, we identified three genes cloned from Lavandula angustifolia. These genes, designated as LaTPS7, LaTPS8, and LaCYP71D582, were hypothesized to be active in plant defense during early developmental stages. The in-vitro assays showed LaTPS7 produced eight compounds including camphene, myrcene, limonene etc. and LaTPS8 catalyzed nine volatiles from α-pinene, sylvestrene to fenchol etc. using geranyl diphosphate (GPP) and nerolidyl diphosphate (NPP) as substrate separately. However, LaTPS7 present in plastids only, synthesized limonene within Nicotiana benthamiana. Limonene was then converted into carveol by LaCYP71D582 present in the endoplasmic reticulum. LaTPS8, also located in plastids, synthesized α-pinene and sylvestrene. Odour response of aphids (Myzus persicae) and ladybugs (Harmonia axyridis) showed that volatiles from transgenic tobacco leaves repelled aphids and attracted ladybugs. LaTPS7 promoter GUS stain assay in Arabidopsis thaliana showed that LaTPS7 displayed a wound-induced expression in leaves. Together, our findings show that these compounds and gene-expression pattern played important roles in protecting plants during vulnerable stages. More practically, these plant tactics can be exploited in agriculture to decrease the use of insecticides, thereby contributing to improved human and environmental health.