PHOTOTROPIN-mediated blue light signaling orients the asymmetry of Marchantia polymorpha spores

The haploid multicellular stage of the plant, Marchantia polymorpha, develops from a single cell – the spore – that divides asymmetrically, producing an apical germ cell that generates the plant body and a smaller basal cell that differentiates as an anchoring germ rhizoid cell.

We show that the orientation of this asymmetric cell division is controlled by an external, environmental cue – blue light – that is perceived by the photoreceptor PHOTOTROPIN and signals in an NCH1-dependent manner. This defines core elements of the mechanism by which a directional environmental signal orients cell division, which in turn orients the first axis of symmetry.