Identification and analysis of phosphorylation status of proteins in dormant terminal buds of poplar

We used mass spectrometry combined with TiO2 phosphopeptide-enrichment strategies to investigate the phosphoproteome of dormant terminal buds (DTBs) in poplar (Populus simonii × P. nigra). There were 161 unique phosphorylated sites in 161 phosphopeptides from 151 proteins; 141 proteins have orthologs in Arabidopsis, and 10 proteins are unique to poplar. Only 34 sites in proteins in poplar did not match well with the equivalent phosphorylation sites of their orthologs in Arabidopsis, indicating that regulatory mechanisms are well conserved between poplar and Arabidopsis. Further functional classifications showed that most of these phosphoproteins were involved in binding and catalytic activity. Extraction of the phosphorylation motif using Motif-X indicated that proline-directed kinases are a major kinase group involved in protein phosphorylation in dormant poplar tissues.This study provides evidence about the significance of protein phosphorylation during dormancy, and will be useful for similar studies on other woody plants.Dormancy is a key feature of perennial plants. During dormancy the meristem becomes insensitive to growth-promoting signals for a period of time, before it is released and growth resumes [1,2]. Bud dormancy is a critical developmental process that allows perennial plants to survive extreme seasonal variations in climate. The regulation of dormancy is a complex process that is necessary for plant survival, development, and architecture [3,4]. A thorough understanding of regulation mechanisms controlling dormancy in woody perennials would have a variety of applications for genetic improvement of woody trees [3,5,6]. Considerable progress has been made in understanding the molecular mechanisms and regulatory pathways involved in bud dormancy [2]. However, until recently such studies focused on regulation at the levels of transcription, post-transcription, and translation [1,7-12]. Despite the importance of dormancy regulation for perennial behavior