Regulatory Networks Participating in Trichome Development

Position-dependent cell fate determination and pattern formation are unique aspects of the development of plant structures. The establishment of single-celled leaf hairs (trichomes) from pluripotent epidermal (protodermal) cells in Arabidopsis thaliana provides a powerful system to determine the genetic/regulatory networks and positional signals involved in cell fate determination.

We have focused on the bHLH transcription factor GL3, as a window to explore the transcriptional regulatory networks that participate in trichome development. We have shown that trichome initiation is triggered within 4 hours of the induction of the GL3 protein function (Figure 1). Within this developmental window, GL3 binds to the promoters of at least three genes previously implicated in the development and patterning of trichomes (GL2, CPC, and ETC1) and activates their transcription. Chromatin immunoprecipitation (ChIP) experiments have shown the in vivo binding of GL3 to the promoters of these genes in the presence of the R2R3-MYB factor GL1, supporting a model in which a GL3-GL1 complex is part of the trichome initiation enhanceosome. In contrast, GL3 is recruited to its own promoter in a GL1-independent manner, resulting in decreased GL3 expression, suggesting the presence of a GL3 negative auto-regulatory loop (Figure 2). In addition to standard ChIP experiments, genome-wide location analyses (chip-chip) resulted in the identification of several novel GL3 and GL1 targets.