Reversible phosphorylation of WOX5 protein controls the homeostasis of QC

Abstract

SummaryFundamental questions of structural and functional homeostasis of theArabidopsisQC in root stem cell niche remain elusive. WUSCHEL-RELATED HOMEOBOX 5 (WOX5) protein, which serves as a QC marker, yet the regulation of its homeostasis remains unknown. Here, we characterize a novel role of PEST domain in WOX5 protein, which stabilizes WOX5 protein by phosphorylating GSK3 Motifs (GMs). Next, we demonstrate that the subfamily II ofArabidopsisSHAGGY-like Kinases (AtSKs) stabilizes WOX5 protein by phosphorylating the GMs in the PEST domain and the subfamily II of the catalytic subunit ofArabidopsisPP2A (AtPP2A-Cs) holoenzymes destabilizes WOX5 protein by dephosphorylating the GMs. Moreover, we find both in situ overexpressed and phosphate-mimicked WOX5 protein can reduce the proliferative activity of the original stele initials (SI) and its daughter cells (SID), leading to the production of more quiescent cells. Taken together, our findings suggest that the homeostasis of WOX5 protein is modulated by reversible phosphorylation, which functionally controls the homeostasis of the QC cells’ low proliferative activity. Furthermore, the subfamily II of AtPP2A-Cs structurally controls the homeostasis of one-layer QC by down-regulating WOX5 expression and destabilizing WOX5 protein in the SI and SID.HighlightsThe subfamily II of AtSKs stabilizes WOX5 protein by phosphorylating the GSK3 Motifs in the PEST domainThe subfamily II of the catalytic subunit of AtPP2A-Cs holoenzymes destabilizes WOX5 protein by dephosphorylating GSK3 MotifsReversible phosphorylation of WOX5 protein controls the homeostasis of the low proliferative activity of the QC cells and of the constant one-layer QCIn situ overexpressed WOX5 protein and phosphate-mimicked WOX5 protein are both sufficient for producing more quiescent cells