Dissecting the Chloroplast Proteome of the Potato (Solanum Tuberosum L.) and Its Comparison with the Tuber Amyloplast Proteome

The chloroplast, the energy organelle unique to plants and green algae, performs many functions, including photosynthesis and biosynthesis of metabolites. However, as the most critical tuber crop worldwide, the chloroplast proteome of potato (Solanum tuberosum) has not been explored. Here, we use Percoll density gradient centrifugation to isolate intact chloroplasts from leaves of potato cultivar E3 and establish a reference proteome map of potato chloroplast by bottom-up proteomics. A total of 1834 non-redundant proteins were identified in the chloroplast proteome, including 51 proteins encoded by the chloroplast genome. Extensive sequence-based localization prediction revealed over 62% of proteins to be chloroplast resident by at least one algorithm. Sixteen proteins were selected to evaluate the prediction result by transient fluorescence assay, which confirmed that 14 were distributed in distinct internal compartments of the chloroplast. In addition, we identified 136 phosphorylation sites in 61 proteins encoded by chloroplast proteome. Furthermore, we reconstruct the snapshots along starch metabolic pathways in the two different types of plastids by a comparative analysis between chloroplast and previously reported amyloplast proteomes. Altogether, our results establish a comprehensive proteome map with post-translationally modified sites of potato chloroplast, which would provide the theoretical principle for the research of the photosynthesis pathway and starch metabolism.