TRANSPARENT TESTA GLABRA1 (TTG1) regulates leaf trichome density in tea (Camellia sinensis)

Plant leaf trichomes not only are an essential trait for taxonomy but also
participate in the resistance to biotic and abiotic stress. Leaf trichomes
vary significantly among different tea varieties, ranging from leaves with
high trichome density to relatively glabrous leaves. Leaf trichomes are a
crucial diagnostic characteristic in tea identification and taxonomy. In
addition, trichomes are also a valued trait in tea production; leaf
trichomes are generally considered to be associated with improved taste.
However, the molecular mechanisms of trichome formation and the genetic
control of trichome density in tea plants remain unknown. In this study,
we identified a gene named TRANSPARENT TESTA GLABRA1 (CsTTG1), which
encodes a WD-repeat protein and is associated with trichome
formation in tea. The results also showed that CsTTG1 is highly expressed
in the top bud of tea, which is consistent with trichome formation in this
tissue. CsTTG1 encodes a protein localized in both the nucleus and
cytoplasm. In addition, the transcription level of CsTTG1 was related to
the length and/or density of the trichomes in different tea cultivars with
diverse leaf trichome densities. Moreover, overexpressing CsTTG1 increased
the number of trichomes in Arabidopsis thaliana. Collectively, our results
indicated that CsTTG1 is involved in regulating trichome formation and
that the expression level of CsTTG1 may be related to trichome density in
tea plants. Our results may facilitate research on tea taxonomy and the
adaptation of tea to its habitats.