Abstract: Land plants developed water-conducting system to survive the drought condition during early plant evolution to colonize land. Several kinds of cells for water-conducting system are known in land plants, such as hydroids of mosses, tracheids of ferns and gymnosperms, and vessel cells of angiosperms. All the water-conducting cells are dead and most of them have thickened plant cell walls (so called secondary cell walls). Our recent efforts identified master regulators, VND6 and VND7 NAC transcription factors, of vessel cell differentiation in model angiosperm, Arabidopsis. Subsequent studies revealed that a gene family, VNS, composed of 13 genes including VND6 and VND7 is regulating differentiation of three different kinds of cells with thickened cell walls in angiosperms. In addition, we showed that VNS genes in a moss, Physcomitrella patens, control the differentiation of hydroids and that VND7-regulated artificial differentiation of vessel cells in Arabidopsis firstly offers us to analyze the fine processes of the differentiation including the dynamics of related proteins. Based on these findings, I would like to discuss about the evolution and revolution of cells contributing to water-conduction in land plants.