Abstract
Root stem cell niche functioning requires the formation and maintenance of the specific “auxin-rich domain” governed by directional auxin transport and local auxin production. Auxin maximum co-localizes with the WOX5 expression domain in the quiescent center that separates mitotically active proximal and distal root meristems. Here we unravel the interconnected processes happening under WOX5 overexpression by combining in vivo experiments and mathematical modeling. We showed that WOX5-induced TAA1-mediated auxin biosynthesis is the cause, whereas auxin accumulation, PIN transporters relocation, and auxin redistribution between proximal and distal root meristems are its subsequent effects that influence the formation of the well-described phenotype with an enlarged root cap. These findings helped us to clarify the role of WOX5, which serves as a local QC-specific regulator that activates biosynthesis of non-cell-autonomous signal auxin to regulate the distal meristem functioning. The mathematical model with WOX5-mediated auxin biosynthesis and auxin-regulated cell growth, division, and detachment reproduces the columella cells dynamics in both wild type and under WOX5 dysregulation.
Highlights
Plant root apical meristem is a classical stem cell niche where an organizing center produces local signals promoting maintenance of the adjacent stem cells
It was believed that the WOX5 transcription factor mobility that generates the WOX5 gradient from the QC to columella stem cells (CSCs) is essential for distal meristem maintenance
This tendency persisted after 48 h of DEX treatment, differentiated columella cells (DCC) layers differentiated before the DEX treatment onset were detached leaving in columella novel 10–12 layers generated from the cells being CSCs or CSC daughters (CSCDs) when the DEX incubation started (Figures 1E,F)
Summary
Plant root apical meristem is a classical stem cell niche where an organizing center (the quiescent center, QC) produces local signals promoting maintenance of the adjacent stem cells (initials). The QC-produced WOX5 (WUSCHEL-RELATED HOMEOBOX 5) transcription factor provides for maintenance of the columella stem cells (CSCs) in the distal meristem (van den Berg et al, 1997; Sarkar et al, 2007; Pi et al, 2015; Berckmans et al, 2020). It was believed that the WOX5 transcription factor mobility that generates the WOX5 gradient from the QC to CSCs is essential for distal meristem maintenance. It was suggested that other non-cell-autonomous regulators originating in the QC exist to maintain the distal meristem together with CLE40-ACR4-CLV1 circuit (Richards et al, 2015; Berckmans et al, 2020). The WOX5 role in distal meristem functioning needs to be revisited
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