Visualization of auxin-mediated transcriptional activation using a common auxin-responsive reporter system in the liverwort Marchantia polymorpha

The phytohormone auxin plays a pivotal role in various developmental aspects in land plants. However, little is known of the auxin response and distribution in non-vascular plants. In this study, we made transgenic plants of the liverwort Marchantia polymorpha which express the uidA (GUS) reporter gene under control of the soybean auxin-inducible promoter, ProGH3, and used it to indirectly monitor auxin-mediated transcriptional activation in planta. Transgenic plants carrying ProGH3:GUS showed GUS activity in an auxin-dependent manner. Histochemical GUS staining was observed at the bottom of gemma cups in the process of vegetative propagation. Significant GUS activity was also detected around the gametophyte-sporophyte junction as well as the developing sporophyte after fertilization. These results suggest that the activity of auxin is crucial in both gametophyte and sporophyte development in M. polymorpha, and that the mechanism for auxin-mediated transcriptional activation had already been established when plants emerged on the terrestrial environment.