Abstract

How changes of genetic mechanism led to the innovation of adaptive traits during origin of land plants still remain open. One of those questions is associated with the innovation of specialized cells for water transport, which enabled the transition from aquatic to terrestrial environment. Recent researches revealed a group of NAC transcription factors VNS (VND/NST/SND) orchestrate the development of xylem cell formation in vascular plants. However, the evolution of these cells is still unclear. Using the moss Physcomitrella patens, a non-vascular plant species, by studying NAC proteins homologous to VNS family in vascular plants, this research elucidated that these genes control the development of water-conducting cell (hydroid) and supporting cell (stereid) by regulating the similar family genes as their homologues function for xylem cell formation in vascular plants, indicating the conservation of VNS -based genetic regulation of water-conducting and supporting cells between moss and vascular plants. In addition, loss-of-function mutants are more prone to wilting when exposed to the condition with lower humidity, suggesting the diversification of NAC proteins to induce the specialized cells for more efficient water conduction was a pivotal event for early plants to maintain water balance when they were first exposed to the dry land.