Gene expression underlying floral epidermal specialization in Aristolochia fimbriata (Aristolochiaceae).

Background and aims The epidermis constitutes the outermost tissue of the plant body. Although it plays major structural, physiological, and ecological roles in embryophytes, the molecular mechanisms controlling epidermal cell fate, differentiation, and trichome development is scarce across angiosperms, and almost unexplored in floral organs. Methods In this study, we assess the spatio-temporal expression patterns of GL2, GL3, TTG1, TRY, MYB5, MYB6, HDG2, MYB106-like, WIN1, and RAV1-like homologs in the magnoliid Aristolochia fimbriata (Aristolochiaceae) by using comparative RNA-seq and in situ hybridization assays. Key results Genes involved in A. fimbriata trichome development vary depending on the organ where they are formed. Stem, leaf and pedicel trichomes recruit most of the transcription factors (TFs) described above. Conversely, floral trichomes only use a small subset of genes including AfimGL2, AfimRAV1-like, AfimWIN1, AfimMYB106-like, and AfimHDG2. The remaining TFs AfimTTG1, AfimGL3, AfimTRY, AfimMYB5, and AfimMYB6 are restricted to the abaxial (outer) and the adaxial (inner) pavement epidermal cells. Conclusions We re-evaluate the core genetic network shaping trichome fate in flowers of an early-divergent angiosperm lineage and show a morphologically diverse output with a simpler genetic mechanism in place when compared to the models Arabidopsis thaliana and Cucumis sativus. In turn, our results strongly suggest that the canonical trichome gene expression appears to be more conserved in vegetative than in floral tissues accross angiosperms.