Protein phosphorylation plays a key role in the synthesis and degradation of dry seed storage proteins. In contrast, no evidence for phosphorylation has been reported to date in vegetative storage proteins (VSPs). The patatin multigene family encodes the major VSP of the potato, Solanum tuberosum L. This study addresses for the first time the identification and mapping of phosphorylated patatin forms based on high-resolution two-dimensional electrophoresis (2-DE) profiles. Patatin isoforms from mature tubers of cultivar Kennebec were separated by 2-DE and subsequently identified by tandem mass spectrometry. In-gel identification and mapping of phosphorylated isoforms were performed using the multiplex phosphoprotein-specific staining Pro-Q DPS. We found that phosphorylation is a ubiquitous post-translational protein modification associated with isoforms of patatin. In addition, protein dephosphorylation with hydrogen fluoride-pyridine coupled to 2-DE was used for quantitative profiling of phosphorylated patatin. This experimental approach showed that patatin comprises multiple isoforms with very different phosphorylation level. Thus, phosphorylation rates over isoforms ranged from 4.6 to 52.3%. Overall, the identification and mapping of differentially phosphorylated patatin opens up new exploratory ways to unravel the molecular mechanisms underlying its mobilization along the tuber life cycle.
Part of the book: Seed Biology