Comparative morphoanatomy and transcriptomic analyses reveal key factors controlling floral trichome development in Aristolochia (Aristolochiaceae)

Trichomes are specialized epidermal cells in aerial plant parts. Trichome development proceeds in three stages, determination of cell fate, specification, and morphogenesis. Most genes responsible for these processes have been identified in the unicellular branched leaf trichomes from the model Arabidopsis thaliana. Less is known about the molecular basis of multicellular trichome formation across flowering plants, especially those formed in floral organs of early diverging angiosperms. Here, we aim to identify the genetic regulatory network (GRN) underlying multicellular trichome development in the kettle-shaped trap flowers of Aristolochia (Aristolochiaceae). We selected two taxa for comparison, A. fimbriata, with trichomes inside the perianth, which play critical roles in pollination, and A. macrophylla, lacking specialized trichomes in the perianth. A detailed morphoanatomical characterization of floral epidermis is presented for the two species. We compared transcriptomic profiling at two different developmental stages in the different perianth portions (limb, tube, and utricle) of the two species. Moreover, we present a comprehensive expression map for positive regulators and repressors of trichome development, as well as cell cycle regulators. Our data point to extensive modifications in gene composition, expression, and putative roles in all functional categories when compared with model species. We also record novel differentially expressed genes (DEGs) linked to epidermis patterning and trichome development. We thus propose the first hypothetical genetic regulatory network (GRN) underlying floral multicellular trichome development in Aristolochia, and pinpoint key factors responsible for the presence and specialization of floral trichomes in phylogenetically distant species of the genus.