Pick a pattern: transcriptional regulator allelic diversity synergistically drives trichome pattern diversity

Trichomes, commonly referred to as plant hairs, are highly specialized from aerial epidermal cells. These structures can be morphologically very diverse: uni- or multicellular, branched or not branched, and glandular or nonglandular. Their ecological functions are also diverse, with predominant roles in plant defense against biotic and abiotic stresses. For example, trichomes can provide a physical and chemical barrier to herbivores, protect against UV damage by absorbing harmful radiation, and buffer against drought stress (Fürstenberg-Hägg et al. 2013; Bickford 2016).

In the model species Arabidopsis thaliana, an intricate network of transcriptional regulators controlling trichome development has been elucidated (Yang and Ye 2013). A trimeric MYB/bHLH/WD-repeat complex, composed of GLABRA1 (GL1), GLABRA3/ENHANCER OF GLABRA2 (GL3/EGL3), and TRANSPARENT TESTA GLABRA1 (TTG1), activates the expression of the homeodomain transcription factor GLABRA2 (GL2), which triggers trichome fate in epidermal cells (Fig.). In addition, another 7 MYB transcription factors act as negative regulators by interfering with the trimeric activation complex.