A Two-Step Model for de Novo Activation of WUSCHEL during Plant Shoot Regeneration

Abstract

Plant cells are totipotent and competent to regenerate from differentiated organs. It has been known for six decades that cytokinin-rich medium induces shoot regeneration from callus cells. However, the underlying molecular mechanism remains elusive. The homeodomain transcription factor WUSCHEL (WUS) is essential for de novo establishment of the shoot stem cell niche in We found that WUS-positive (WUS) cells mark the shoot progenitor region during regeneration. A cytokinin-rich environment initially promotes the removal of the repressive histone mark H3K27me3 at the locus in a cell cycle-dependent manner. Subsequently, the B-type ARABIDOPSIS RESPONSE REGULATORs (ARRs) ARR1, ARR2, ARR10, and ARR12, which function as transcriptional activators in the cytokinin signaling pathway, spatially activate expression through binding with microRNA165/6-targeted HD-ZIP III transcription factors. Thus, our results provide important insights into the molecular framework for cytokinin-directed shoot regeneration and reveal a two-step mechanism for de novo activation of .

Thioredoxin-Mediated ROS Homeostasis Explains Natural Variation in Plant Regeneration

“…The correct distribution of auxin and cytokinin is essential for WUS induction during de novo shoot 71 regeneration (Cheng et al, 2013 (Meng et al, 2017;Zhang et al, 2017).…”

Root stem cell niche organizer specification by molecular convergence of PLETHORA and SCARECROW transcription factor modules

“…In the shoot apical meristem, the WOX5 sister protein WUS defines the organizing center for the overlying stem cells, and its expression domain is generated by different genetic programs to maintain the shoot stem cell niche (Meng et al 2017;Zhang et al 2017a,;Zubo et al 2017). During initiation of the embryonic shoot stem cells, a WOX2 module promotes the expression of HD-ZIPIII genes to ensure the appropriate ratio of cytokinin and auxin pathways (Zhang et al 2017b).…”

“…During initiation of the embryonic shoot stem cells, a WOX2 module promotes the expression of HD-ZIPIII genes to ensure the appropriate ratio of cytokinin and auxin pathways (Zhang et al 2017b). During de novo shoot regeneration, cytokinin B-type Arabidopsis response regulators (ARRs) combine with HD-ZIP III coactivators for region-specific activation of the WUS promoter (Zhang et al 2017a), whereas, in the SAM, ARRs appear to maintain mainly WUS expression (Meng et al 2017;Zhang et al 2017a). WUS expression is restricted by the stem cell-expressed CLAVATA3 (CLV3) peptide and interacting receptor kinase pathways (Clark et al 1997;Brand et al 2000;Schoof et al 2000;Müller et al 2008;Ogawa et al 2008;Nimchuk et al 2011).…”

“…Over the last two decades, research in animals and plants has revealed examples of considerable plasticity in the specification of organizer cells (Boyer et al 2006;Wilson et al 2008;Tian et al 2011;Dejana et al 2017;Hoeck et al 2017). A dramatic demonstration of this plasticity in plants is the regeneration of an entirely new stem cell niche upon surgical dissection (Xu et al 2006;Efroni et al 2016;Zhang et al 2017a). In both roots and shoots, this leads to the re-establishment of a new domain of expression of WOX5/WUS.…”

DNA METHYLTRANSFERASE1‐mediated shoot regeneration is regulated by cytokinin‐induced cell cycle in Arabidopsis

“…At the early stage of shoot induction, ARRs are widely expressed in the callus, but WUS is not activated (Meng et al ., ; Zhang et al ., ), implying that other factors might repress WUS expression. Several studies have shown that histone modifications, H3K9me2 and H3K27me3, as well as DNA methylation, can repress WUS expression in the callus (Li et al ., ; Zhang et al ., ). Reduced DNA methylation levels by the mutation of MET1 can lead to the early emergence of the WUS signal in the process of shoot induction (Li et al ., ).…”