Regulation of CLV3 Expression by Two Homeobox Genes in Arabidopsis

Abstract

The ability of meristems to continuously produce new organs depends on the activity of their stem cell populations, which are located at the meristem tip. In Arabidopsis, the size of the stem cell domain is regulated by two antagonistic activities. TheWUS (WUSCHEL) gene, encoding a homeodomain protein, promotes the formation and maintenance of stem cells. These stem cells express CLV3(CLAVATA3), and signaling of CLV3 through the CLV1/CLV2 receptor complex restricts WUS activity. Homeostasis of the stem cell population may be achieved through feedback regulation, whereby changes in stem cell number result in corresponding changes inCLV3 expression levels, and adjustment ofWUS expression via the CLV signal transduction pathway. We have analyzed whether expression ofCLV3 is controlled by the activity of WUSor another homeobox gene, STM (SHOOT MERISTEMLESS), which is required for stem cell maintenance. We found that expression of CLV3 depends onWUS function only in the embryonic shoot meristem. At later developmental stages, WUS promotes the level ofCLV3 expression, together with STM. Within a meristem, competence to respond to WUS activity by expressing CLV3 is restricted to the meristem apex.