Chloroplast Pinch

Kristian Peters — Fabelfroh (Chloroplast)

The paper

Y. Yoshida et al., "Chloroplasts divide by contraction of a bundle of nanofilaments consisting of polyglucan," Science, 329:949-53, 2010. Free F1000 Evaluation

The finding

When a cell divides, it splits its organelles so that each daughter has the right starting material. But rather than using a band of proteins, Tsuneyoshi Kuroiwa at Rikkyo University and colleagues found that chloroplasts divide via a contractile ring made of starch-like fibers called polyglucans.

The surprise

Mitochondrial division occurs with the help of a contractile ring made from proteins, and although the mechanism in chloroplasts was unknown, researchers assumed it would be similar. Faculty Member Jim Umen calls it “pretty remarkable” that the structural element for division is a polysaccharide.

The squeeze

The red alga Cyanidioschyzon merolae only has a single chloroplast and mitochondrion, which divide synchronously during cell division. Kuroiwa’s group isolated the...

The unknown

“The quality of data is outstanding,” says Faculty Member Wataru Sakamoto. But it’s only a start: PDR1 doesn’t have clear homologs in higher plants or green algae. So whether a similar protein is involved in a model system such as Arabidopsis is a mystery. The actual mechanism—how a polysaccharide fiber can generate force—is also unknown. “It’s out there for somebody to figure out,” says Associate Faculty Member Brad Olson.

F1000 evaluators: W. Sakamoto (Okayama University) • B. Olson and J. Umen (The Salk Institute)

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