Micromorphology and Molecular Insights Into Glandular Trichomes in Two
Different Thymes: Glandular Trichomes Formation Process and the Function
of the Main Regulator TqHD1
Abstract
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.