Overexpression of NtWoolly and NtMYB GR1 induces glandular trichome development in Nicotiana tabacum

Trichomes are uni- or multicellular epidermal protuberances originating from the protoderm and located on the aerial parts of plants. Generally, they are separated into two groups: glandular and non-glandular trichomes. Depending on their nature and location, these specialized structures are involved in different plant mechanisms. Roughly, glandular trichomes store and/or secrete various chemical substances to repel or deter pathogens and insects, whereas non-glandular trichomes mainly provide plants with biophysical barriers. Moreover, due to their ability to secrete chemical substances, genetically engineered glandular trichomes are useful to produce desired molecules in large amounts or to protect crop species. However, in order to make glandular trichomes a great biotechnological tool, it is necessary to characterize and understand the mechanisms governing their development. Unlike the development of Arabidopsis thaliana non-glandular trichome which is widely characterized, information about the regulation of Nicotiana tabacum glandular trichome initiation is quite limited. Moreover, many researchers reported results indicating that the development of the two trichome types are under the control of different genetic mechanisms. In this context, the goal of this Master thesis was to overexpress two genes, NtWoolly and NtMYB GR1, encoding transcription factors putatively involved in the development of tobacco multicellular glandular trichome. To do so, NtWoolly and NtMYB GR1 were transferred through Agrobacterium-mediated transformation in expression vectors, the pH7WG2 and pH7WG2D plasmids respectively, where their expression is under the control of a constitutive promoter. Also, we generated transgenic tobacco lines transformed with pMDC7 plasmids where both genes are under the control of an inducible promoter. In addition, we performed RT-qPCR analyzes on wild-type tobacco plants to assess the expression pattern of both genes. The results indicated that both transcription factors are expressed in a constitutive manner in most tobacco organs and tissues with leaf trichomes showing the highest expression level. Qualitative screening and trichomes counting on tobacco plants overexpressing either NtWoolly or NtMYB GR1, under the controle of a constitutive promoter, exhibited a significantly higher long glandular trichome density in T0 transgenic lines than in wild-type plants without altering trichome morphology. Finally, even if the results presented in this Master thesis are still preliminary and need to be further confirmed by the analysis of the next generation of transgenic plants, NtWoolly and NtMYB GR1 seem to be two promising candidates involved in tobacco glandular trichome initiation and development.