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 mossPhyscomitrium patenshas recently been developed as a model to dissect the genetic basis of 3D growth, an invariable and unifying feature of all land plants. The cytokinin-unresponsivePpnog1-Rmutant incorrectly orients division planes in developing buds and thus fails to make the transition to 3D growth. To reveal the genetic interactors of thePpNOG1gene, which encodes a protein with a C-terminal UBA domain, we performed a screen and identified thesuppressor of nog1a(snog1a) mutant. We have mapped the causative mutation to a gene that encodes a prion-like protein related to FLOE2/3 and demonstrated that the mutant phenotypes observed in both anog1disruptant mutant (nog1dis) andsnog1acan be attributed to changes in cytokinin perception. We present a revised model for 3D growth and suggest that the 2D-to-3D growth transition is regulated, at least in part, by liquid-liquid phase separation (LLPS).SUMMARY STATEMENTThe transition to 3D growth is negatively regulated by a prion-like protein that both alters cytokinin signaling and has been implicated in liquid-liquid phase separation (LLPS).