A FLOE-related protein regulates the 2-dimensional to 3-dimensional growth transition in the moss Physcomitrium patens

The colonization of the land by plants coincided with the evolution of 3-dimensional (3D) growth; the acquisition of apical cells with the capacity to rotate the plane of cell division. The moss Physcomitrium patens has recently been developed as a model system in which to dissect the genetic basis of 3D growth, a unifying feature of all land plants. The cytokinin-unresponsive Ppnog1-R mutant incorrectly orients division planes in developing buds and thus fails to make the transition to 3D growth. To reveal the genetic interactors of the PpNOG1 gene, which encodes a protein with a C-terminal UBA domain, we performed a screen and identified the suppressor of nog1a (snog1a) mutant. We have mapped the causative mutation to a gene that encodes a prion-like protein related to FLOE2/3 from Arabidopsis and demonstrated that the mutant phenotypes observed in both a nog1 disruptant mutant (Ppnog1dis) and snog1a can be attributed to changes in cytokinin perception. We present a revised model in which PpNOG1 operates independently of the PpAPB transcription factors to promote 3D growth initiation.