Countless cellular processes are regulated by protein phosphorylation. Kinases transfer the phosphate groups to specific target proteins. Addition of a phosphate group may affect the activity or the ability of the substrate to interact with other proteins. Phosphatase activity is directly opposite to kinase activity and removes phosphate groups from target proteins reversing its effects. In agreement with the large number of processes regulated by protein phosphorylation the Arabidopsis genome accounts for an estimated 1160 kinases. However, surprisingly few predicted kinases (around a dozen) are present in chloroplasts. The best studied of these kinases are STN7 and STN8 implicated in state transition and D1 repair at the thylakoid membrane and thus function to optimize photosynthetic activity at the protein level. In contrast, the non-typical ABC1-like kinases (ABC1Ks) in chloroplasts reside on lipid droplets (plastoglobules, PG) and function to optimize photosynthesis by modifying the neutral lipid composition of the thylakoid membrane. This includes key electron transporters (plastoquinone and phylloquinone), antioxidants (tocopherols) and photoprotectants (carotenoids). This project aims at unraveling the ABC1K phosphoprotein network using state of the art techniques including phosphoproteomics using the Chlorophos 1.0 peptide chip covering the known chloroplast phosphoproteome and lipidomics to analyze the downstream effects of target phosphorylation. The question whether the prototypical ABC1-like is itself a target of kinase regulation will be addressed. By analyzing the known ABC1K target, tocopherol cyclase (VTE1) we will determine whether phosphorylation affects activity of the enzyme or its attachment to its site of action, the lipid droplets. The effects of ABC1K activity on lipid droplet protein and lipid composition will also be determined. The results will give important insight in the activity of the major group of chloroplast kinases and give way to translation into crop plants such as tomato.