Proteins turn plants into well-oiled machines

MICHIGAN STATE (US) — The discovery of a new class of proteins may lead to improvements in crops through breeding or genetic manipulation, new research shows.

The proteins, called Clumped Chloroplasts, play a key role in helping chloroplasts separate when they divide. The proteins are also critical in the perpetuation of chloroplasts during cell division. Chloroplasts are responsible for the process of photosynthesis.

The research is reported in Proceedings of the National Academy of Sciences.

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Green chloroplasts in plant cells are essentially molecular factories where carbon dioxide from air is used to produce sugar, which is food for plants. When leaves are growing, chloroplasts increase their numbers dramatically by dividing in half.  A single leaf cell can end up having more than 100 chloroplasts.

The expanded chloroplast population boosts photosynthesis and subsequently increases the plant’s growth. CLMP1 is one of many proteins that work together like a well-oiled machine to help chloroplasts divide and multiply.

Studying mutant Arabidopsis thaliana plants that failed to produce CLMP1, researchers saw that the chloroplasts had nearly completed the division process, but had failed to separate, instead remaining connected to each other through thin membranes.

“The mutant plants had chloroplasts that appeared like clusters of grapes,” says Katherine Osteryoung, a plant biologist at Michigan State University, who was recently named an AAAS Fellow.

“In normal plants, chloroplasts are separated and distributed throughout cells. This enables the chloroplasts to move freely around the cell to maximize photosynthesis. In the mutant, where the chloroplasts remain bunched together, they cannot move around as freely, which probably impairs photosynthesis. The discovery of CLMP1 helps explain how plants have evolved mechanisms to promote chloroplast division and dispersal and avoid clumping.”

In normal plants, the separation and distribution of chloroplasts also helps ensure that, when cells divide, each daughter cell inherits about half of the chloroplasts. Further investigation demonstrated that CLMP1 is required for this normal inheritance of chloroplasts during cell division.

Since genes closely related to CLMP1 are also present in crop plants, Osteryoung’s research could lead to improvements in corn, wheat, soybeans, and other food crops.

“In the long run, this could lead to improvements in crops through breeding and/or genetic manipulation for improved chloroplast distribution,” Osteryoung saYS.

Scientists from the University of Toronto and the University of California, San Francisco, contributed to the study, which was supported by the U.S. Department of Energy, the National Science Foundation, and MSU’s AgBioResearch.

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