Modification-specific proteomics in plant biology

Post-translational modifications (PTMs) are involved in the regulation of a wide range of biological processes, and affect e.g. protein structure, activity and stability. Several hundred PTMs have been described in the literature, but relatively few have been studied using mass spectrometry and proteomics. In general, methods for PTM characterization are developed to study yeast and mammalian biology and later adopted to investigate plants. Our point of view is that it is advantageous to enrich for PTMs on the peptide level as part of a quantitative proteomics strategy to not only identify the PTM, but also to determine the functional relevance in the context of regulation, response to abiotic stress etc. Protein phosphorylation is the only PTM that has been studied extensively at the proteome wide level in plants using mass spectrometry based methods. We review phosphoproteomics studies in plants and discuss the redox mediated PTMs (S-nitrosylation, tyrosine nitration and S-glutathionylation), ubiquitylation, SUMOylation, and glycosylation, including GPI anchors, and the quantitative proteomics methods that are used to study these modification in plants. Where appropriate we contrast the methods to those used for mammalian PTM characterization.