Comparative phosphoproteomic analysis reveals differentially phosphorylated proteins regulate anther and pollen development in kenaf cytoplasmic male sterility line

Cytoplasmic male sterility (CMS) is widely used in plant breeding and represents a perfect model to understand cyto-nuclear interactions and pollen development research. Protein phosphorylation is ubiquitous and is involved in the regulation of diverse cellular processes. To reveal the possible mechanism of CMS and pollen development in kenaf, we performed an iTRAQ-based comparative phosphoproteome analysis in the anthers of a CMS line and wild-type plant (Wt). Whole transcriptome unigenes of kenaf as the reference genome, we identified a total of 3045 phosphorylated sites on 1640 peptides corresponding to 974 unique proteins. 292 of the peptides which corresponding to 247 unique proteins were differentially phosphorylated (fold change ae 1.20 with P value < 0.05) between these two materials. 113 and 134 proteins were characterized as up-regulated or down-regulated phosphorylated, respectively. An evaluation of the phosphoproteome and proteomic results indicated that the most significantly phosphorylated proteins were not associated with abundant changes at the protein level. Bioinformatics analysis demonstrated that many of these proteins were involved in various biological processes which may play key roles in pollen development, including carbohydrate metabolism, energy metabolism, transport, gene expression regulation, signal transduction, and cell cycle control. Our results provide insight into the CMS mechanism and pollen development in kenaf from a protein phosphorylation perspective.