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From Cyanobacteria to Chloroplasts

Chloroplasts belong to a family of plant specific organelles called plastids. The most prominent feature of chloroplasts is their ability to carry out oxygenic photosynthesis, present also in photosynthetic bacteria.

Chloroplasts originated from an endosymbiotic event, by which a photosynthetic prokaryote was engulfed by an early eukaryotic host. The photosynthetic endosymbiont was most likely an early relative of today's cyanobacteria. During endosymbiosis most of the organellar genes were transferred to the host nucleus. Consequently the products of the transferred genes, i.e. the proteins, had to be targeted back into the organelle. The protein import machinery as we see it today is composed of cyanobacterial derived subunits and proteins, which newly developed during endosymbiosis. The protein import translocons in the outer and inner envelope of chloroplasts (Toc and Tic) act jointly and cooperate in the translocation of proteins with cytosolic proteins as well as with stroma proteins. The imported proteins continue their way to the thylakoids through soluble import intermediates. However thylakoid biogenesis requires also a vesicular transport system.

Chloroplasts cannot be made de novo, but multiply by division and are generally inherited maternally. Chloroplasts still use the bacterial FtsZ system for division, however other factors might have been acquired during endosymbiosis to adapt the process to the need of the eucaryotic cell.

The large biosynthetic capacity of chloroplasts requires the massive exchange of metabolites by transports in the inner envelope an selective ion channels in the outer envelope membrane.

Our work focuses around these fascinating aspects of molecular cell biology.