Abstract

Plant form is the outcome of the tightly regulated division of stem cells within meristems. In flowering plants the CLE gene CLV3 is a key player in this regulation and limits meristem size by restricting stem cell identity to the central meristematic zone. However, although all land plants grow from meristems it is not known if CLE genes also control stem cell number in early diverging land plant lineages. I am using the moss Physcomitrella patens to investigate the function of CLEs in one such plant. P. patens has a single stem cell at the tip of each organ and loss of CLE function causes defects in the apical stem cell division plane. This leads to larger meristems and an increased number of leaf tips. Localised expression of CLE is necessary to maintain wild type stem cell function, which suggests a conserved role for CLE in regulating the stem cell niche. This is the first evidence that the same genetic components regulate stem cell formation in land plants separated by 450 million years of evolution and is particularly interesting as it suggests that the genetic control of plant stem cell identity may be universal.