Phosphoproteomic Analysis of Paper Mulberry under Chilling

Paper mulberry as a valuable woody species has a well chilling tolerance. In this study, phosphoproteomic analysis in combination with physiological measurement and mRNA quantification were employed to explore the molecular mechanism of chilling (4 °C) tolerance in paper mulberry. After chilling for 6 hours, there were 427 significant changed phosphoproteins detected in paper mulberry seedlings without obvious physiological injury. When obvious physiological injury occurred after chilling for 48 hours, a total of 611 phosphoproteins were found significantly change at phosphorylation level. According to 9 phosphorylation motifs extracted by Motif-X analysis, MAPKs, CDPKs, CDKs and CKs were considered as the primary upstream protein kinases. Results of GO analysis showed that phosphoproteins were mainly responsible for signal transduction, protein modification and translation during chilling. Additionally, transport and cellular component organization were respectively enriched after chilling for 6 and 48 hours. Based on the analysis of protein-protein interaction network, a protein kinases and phosphatases hub protein was thought as the key of phosphorylation regulation, which probably modulates cross-talk between Ca2+, BR, ABA and ethylene mediated signaling pathways. Together with results, we concluded a schematic chilling tolerance mechanism at phosphorylation level.