Overlapping and Distinct Roles of HAM Family Genes in Arabidopsis Shoot Meristems

In Arabidopsis shoot apical meristems (SAMs), a well-characterized regulatory loop between WUSCHEL (WUS) and CLAVATA3 (CLV3) maintains stem cell homeostasis by regulating the balance between cell proliferation and cell differentiation. WUS proteins, translated in deep cell layers, move into the overlaying stem cells to activate CLV3. The secreted peptide CLV3 then regulates WUS levels through a ligand-receptor mediated signaling cascade. CLV3 is specifically expressed in the stem cells and repressed in the deep cell layers despite presence of the WUS activator, forming an apical-basal polarity along the axis of the SAM. Previously, we proposed and validated a hypothesis that the HAIRY MERISTEM (HAM) family genes regulate this polarity, keeping the expression of CLV3 off in interior cells of the SAM. However, the specific role of each individual member of the HAM family in this process remains to be elucidated. Combining live imaging and molecular genetics, we have dissected the conserved and distinct functions of different HAM family members in control of CLV3 patterning in the SAMs and in the de novo shoot stem cell niches as well. ; © 2020 Han, Geng, Guo, Yan, Meyerowitz, Liu and Zhou. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms. Received: 11 March 2020; Accepted: 19 August 2020; Published: 04 September 2020. Edited by: Patrick Laufs, Institut National de la Recherche Agronomique (INRA), France. Reviewed by: David Jackson, Cold Spring Harbor Laboratory, United States. Mitsuhiro Aida, Kumamoto University, Japan. The authors thank the Purdue Bindley Bioscience Imaging Facility for access to the ZEISS LSM880 Laser ...