Core pathways controlling shoot meristem maintenance.

Essential to the function of shoot meristems in plants to act as sites of continuous organ and tissue formation is the ability of cells within the meristem to remain undifferentiated and proliferate indefinitely. These are characteristics of the stem cells within meristems that are critical for their growth properties. Stem cells are found in tight association with the stem cell niche-those cells that signal to maintain stem cells. Shoot meristems are unique among stem cell systems in that the stem cell niche is a constantly changing population of recent daughter stem cells. Recent progress from Arabidopsis and other systems have uncovered a large number of genes with defined roles in meristem structure and maintenance. This review will focus on well-studied pathways that represent signaling between the stem cells and the niche, that prevent ectopic differentiation of stem cells, that regulate the chromatin status of stem cell factors, and that reveal intersection of hormone signaling and meristem maintenance.