The Protein Modifications of O-GlcNAcylation and Phosphorylation Mediate Vernalization Response for Flowering in Winter Wheat.

ABSTRACT

O-GlcNAcylation and phosphorylation are two posttranslational modifications that antagonistically regulate protein function. However, the regulation of and the cross talk between these two protein modifications are poorly understood in plants. Here we investigated the role of O-GlcNAcylation during vernalization, a process whereby prolonged cold exposure promotes flowering in winter wheat (Triticum aestivum), and analyzed the dynamic profile of O-GlcNAcylated and phosphorylated proteins in response to vernalization. Altering O-GlcNAc signaling by chemical inhibitors affected the vernalization response, modifying the expression of VRN genes and subsequently affecting flowering transition. Over a vernalization time-course, O-GlcNAcylated and phosphorylated peptides were enriched from winter wheat plumules by Lectin weak affinity chromatography and iTRAQ-TiO2, respectively. Subsequent mass spectrometry and gene ontology term enrichment analysis identified 168 O-GlcNAcylated proteins that are mainly involved in responses to abiotic stimulus and hormones, metabolic processing, and gene expression; and 124 differentially expressed phosphorylated proteins that participate in translation, transcription, and metabolic processing. Of note, 31 vernalization-associated proteins were identified that carried both phosphorylation and O-GlcNAcylation modifications, of which the majority (97%) exhibited the coexisting module and the remainder exhibited the potential competitive module. Among these, TaGRP2 was decorated with dynamic O-GlcNAcylation (S87) and phosphorylation (S152) modifications, and the mutation of S87 and S152 affected the binding of TaGRP2 to the RIP3 motif of TaVRN1 in vitro. Our data suggest that a dynamic network of O-GlcNAcylation and phosphorylation at key pathway nodes regulate the vernalization response and mediate flowering in wheat.