Characterization of two “RAX2-like” genes, potentially involved in the development of Nicotiana tabacum glandular trichomes

Details

Supervisors

Hachez, Charles ; Ramirez, Aldana Mariel

Faculty

Faculté des bioingénieurs

Degree label

Master [120] : bioingénieur en chimie et bioindustries

Abstract

Trichomes are uni- or multicellular outgrowths on the epidermis of the aerial parts of the plants. Trichomes are very diverse in term of structures and morphology and can be either non-glandular or glandular structures. Typically, glandular trichomes store and/or secrete compounds, forming a chemical barrier on the epidermis, repelling pathogens and insects while non-glandular trichomes act more like a physical barrier. While Arabidopsis thaliana is the classical model for the study of non-glandular trichome development, a process which is currently rather well characterized, the development of glandular trichome in other species is not well understood. Nicotiana tabacum could be an interesting model to study the mechanisms of glandular trichomes initiation and regulation since it belongs to the Solanaceae family, which includes several species having a commercial interest (Solanum lycopersicum, Solanum tuberosum,…). To identify and characterize genes involved in the mechanisms of glandular trichomes development in Nicotiana tabacum, transcriptome analysis was performed on transgenic tobacco plants showing a higher trichome density as phenotype. Two RAX2-like genes (NtRAX2.1-2 and NtRAX2.3-2) emerged from this study. They are transcription factors belonging to the MYB family. RAX2-like genes are known to be involved in cell differentiation and developmental processes. The goal of this Master thesis is to characterise these genes. To do so, the study was split in three work phases. First, RT-qPCR of each gene was performed on several plant tissues to determine the gene expression level in these specific tissues. Then, transgenic plants overexpressing these RAX2-like genes were generated to establish a link between gene overexpression and trichome density. Finally, the endogenous transcriptional promoters were cloned and transcriptional reporter lines (nlsGFP-GUS reporter) were created to see where the gene are expressed at the cellular level. The results showed that NtRAX2.3-2, unlike NtRAX2.1-2, is constitutively expressed in all tissues (except the stem) and that its expression is higher in roots and trichomes. Trichome counting on T0 transgenic lines overexpressing either NtRAX2.1-2 or NtRAX2.3-2 indicated that there is a potential increase in trichome density for the transgenic lines that however needs to be further confirmed. No results for the transcriptional reporter lines were recorded. Therefore, further studies are required to further characterize the involvement of both RAX2-like genes in glandular trichome development in Nicotiana tabacum.