PLoS Genet. 11, e1005207 (2015)

Auxin is central to many aspects of plant development. The molecular mechanism leading to transcriptional changes is well understood, and significant complexity was thought to arise from the high number of components in each functional subfamily, which have overlapping spatiotemporal specificities and work in combination. But now, a plant with an unadorned pathway has been found. John Bowman and colleagues describe auxin signalling in the liverwort Marchantia polymorpha. The conserved but extremely simplified mechanism, with only one orthologue representing each subfamily, makes it the simplest known auxin pathway.

The authors first describe how manipulation of auxin content affects Marchantia development. Auxin sensitivity and plant architecture can be modified by transgenic disruption or overexpression of each signalling component. A severely auxin-insensitive plant almost completely loses its body organization, showing that a minimal set of conserved auxin components is enough to pilot plant development and establish a structured body pattern.

As a descendant of the earliest terrestrial plants, Marchantia is an interesting model for evolutionary studies of signalling pathways, and their importance in land colonization. Moreover, its genetic simplicity, vigorous growth, and the now available tools could soon make this plant a model background system for synthetic biology.