Significantly enriched phosphorylation motifs from up-regulated phosphopeptides by Motif-X analysis. Significantly enriched phosphorylation motifs from up-regulated phosphopeptides by Motif-X analysis. The IPI Arabidopsis protein database was used as the background database to normalize the score against random peptide sequences. Motifs 1, SnRK2 kinase family motif; Motif 2, CKII motif; Motif 3 and 4, unknown phosphorylation motifs. Liang Xue et al. Mol Cell Proteomics 2013;12:2354-2369 © 2013 by The American Society for Biochemistry and Molecular Biology, Inc.