Abstract
The phytohormone auxin regulates most aspects of plant growth and development. To understand the origin and evolution of auxin signaling in land plants, we utilized the basal land plant Marchantia polymorpha. We have previously isolated three ARFs (MpARFs), one AUX/IAA (MpIAA), and one TIR1/AFB (MpTIR1) gene from the M. polymorpha genome, implying that M. polymorpha and flowering plants share common auxin-signaling factors. To investigate the role of auxin in the development of M. polymorpha, we generated transgenic plants expressing an mDII-GR fusion protein consisting of degron-modified MpIAA, which dominantly reduces auxin sensitivity, and a C-terminally fused glucocorticoid receptor domain. Dexamethasone (DEX) treatment successfully reduced sensitivity to auxin in these mDII-GR plants. In the presence of DEX, mDII-GR gemmae developed into clumps of cells without forming any organs, such as rhizoids or air chambers, suggesting that auxin signaling mediated by MpIAA contributes to organogenesis from gemma. Based on the detailed observation of mDII-GR plants, we will discuss the role of auxin in the development of M. polymorpha.
