WUSCHEL-mediated cellular feedback network imparts robustness to stem cell homeostasis

Abstract

Shoot apical meristem (SAM) stem cell niche is an interconnected network of distinct cell types; the central zone (CZ) harbors a small pool of stem cells, the stem cell progeny are displaced into the adjacent peripheral zone (PZ) and the rib zone (RZ) located beneath the CZ where they differentiate. Relative ratios of cell types remain constant. Genetic studies have shown that the levels or spatial confinement of WUS, a homeodomain transcription factor to few cells in the RZ is critical for regulating stem cell number. However, static analyses of terminal mutant phenotypes have not revealed WUS-mediated mechanisms of stem cell homeostasis. In a recent study we have employed transient manipulation of WUS levels and live imaging to show that it controls several interdependent processes such as regulation of stem cell number, cell division rates of stem cell progenitors and their patterns of differentiation, thus providing robustness to the process.

Figure 1

A schematic representation of dynamic readjustment of relative ratios of stem cells and differentiating cells of Arabidopsis SAMs to different levels of WUSCHEL. (A) A steady-state condition for a given amount of WUS. (B) A transient increase in WUS levels within the central region results in both the expansion of the stem cell domain/the CZ and increase in cell division rates of differentiating daughters within the PZ. (C) A transient decrease in WUS levels leads to a reduction in cell division rates of the PZ cells, a shift in differentiation program closer to the CZ along with an increase in organ primordia size.