ULTRAPETALA1 maintains Arabidopsis root stem cell niche independently of ARABIDOPSIS TRITHORAX1

• During plant development, morphogenetic processes rely on the activity of meristems. Meristem homeostasis depends on a complex regulatory network constituted by different factors and hormone signaling that regulate gene expression to coordinate the correct balance between cell proliferation and differentiation. • ULTRAPETALA1, a transcriptional regulatory protein described as an Arabidopsis Trithorax group factor, has been characterized as a regulator of the shoot and floral meristems activity. Here, we highlight the role of ULTRAPETALA1 in root stem cell niche maintenance. • We found that ULTRAPETALA1 is required to regulate both the quiescent center cell division rate and auxin signaling at the root tip. Furthermore, ULTRAPETALA1 regulates columella stem cell differentiation. • These roles are independent of the ARABIDOPSIS TRITHORAX1, suggesting a different mechanism by which ULTRAPETALA1 can act in the root apical meristem of Arabidopsis. This work introduces a new component of the regulatory network needed for the root stem cell niche maintenance.