Abstract

SUMMARYPlant stem cells in the shoot apical meristem (SAM) and root apical meristem (RAM) provide for postembryonic development of above-ground tissues and roots, respectively, while secondary vascular stem cells sustain vascular development1–4. WUSCHEL (WUS), a homeodomain transcription factor expressed in the rib meristem of the SAM, is a key regulatory factor controlling stem cell populations in the Arabidopsis SAM5–6 and is thought to establish the shoot stem cell niche via a feedback circuit with the CLAVATA3 (CLV3) peptide signaling pathway7. WUSCHEL-RELATED HOMEOBOX5 (WOX5), specifically expressed in root quiescent center (QC), defines QC identity and functions interchangeably with WUS in control of shoot and root stem cell niches8. WOX4, expressed in Arabidopsis procambial cells, defines the vascular stem cell niche9–11. WUS/WOX family proteins are evolutionarily and functionally conserved throughout the plant kingdom12 and emerge as key actors in the specification and maintenance of stem cells within all meristems13. However, the nature of the genetic regime in stem cell niches that centers on WOX gene function has been elusive, and molecular links underlying conserved WUS/WOX function in stem cell niches remain unknown. Here we demonstrate that the Arabidopsis HAIRY MERISTEM (HAM)family transcription regulators act as conserved interacting co-factors with WUS/WOX proteins. HAM and WUS share common targets in vivo and their physical interaction is important in driving downstream transcriptional programs and in promoting shoot stem cell proliferation. Differences in the overlapping expression patterns of WOX and HAM family members underlie the formation of diverse stem cell niche locations, and the HAM family is essential for all of these stem cell niches. These findings establish a new framework for the control of stem cell production during plant development.

Highlights

  • We constructed various deleted derivatives of HAIRY MERISTEM1 (HAM1) and WUS for yeast-two-hybrid assays to identify essential regions for their interactions

  • We demonstrate that the Arabidopsis HAIRY MERISTEM (HAM)family transcription regulators act as conserved interacting co-factors with WUS/WOX proteins

  • HAM and WUS share common targets in vivo and their physical interaction is important in driving downstream transcriptional programs and in promoting shoot stem cell proliferation

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Summary

Introduction

We constructed various deleted derivatives of HAM1 and WUS for yeast-two-hybrid assays to identify essential regions for their interactions. Deleting amino acids from 117 to 230(D117-230) in HAM1abolished the interaction (Extended Data Fig. 2a). This N-terminal fragment is important for HAM1 function in stem cell maintenance, asHAM1 (D117-230)did not complement the ham1;2;4early termination phenotype, while full-length HAM1 driven by the same HAM1 promoter did(Extended Data Fig. 2b–g), and it is conserved in HAM proteins from Arabidopsis and across different plant species (Extended Data Fig. 2h–j). Deletion analyses of WUS identified a C-terminal region required for interaction with HAM1 (Extended Data Fig. 3a), which is required for WUS function (Extended Data Fig. 3b–d) and is conserved in different plant species (Extended Data Fig. 3e)

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