Isolation of High-Quality Plastids from the Diatom Phaeodactylum tricornutum

Phaeodactylum tricornutum, a model pennate diatom, carries a secondary plastid surrounded by four membranes. Its biological function remains mysterious, supposed to combine features of the primary chloroplast and the endomembrane system. Isolation of high-quality plastid from the diatom enables a more conclusive understanding of the special structure and metabolic pathways in the plastid. Due to the direct continuity between the chloroplast endoplasmic reticulum membrane (cERM) and the outer nuclear envelope together with the integration of cERM into the cellular endoplasmic reticulum (ER) system, the plastid isolation is still challenging. In this study, highly purified P. tricornutum plastids with the four-layered membrane are obtained by Percoll density gradient centrifugation. The isolated plastids are unlikely to contain any residue of nuclear and coatomer compartments, and they might contain a relatively small contamination of mitochondrion and ER debris.