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More than a billion years ago, a relationship began between the ancestor of all living plants and a type of bacteria that paved the way for the evolution of life. as we know it. The ancestor of unicellular algae has engulfed, but not especially destroyed, an organism similar to a cyanobacterium with which it has established a mutually beneficial link. This symbiotic relationship provided energy in the form of sugars derived from photosynthesis (by which sunlight is converted into chemical energy) from cyanobacteria to its host.
The symbiotic cell eventually became the first chloroplast. Even nowadays, these organelles are independent organisms with their own DNA and a double membrane. During evolution, several genes encoded by chloroplasts were transferred into the nuclear genome of the host. Thus, in modern plant and algal cells, many nuclear-coded chloroplast proteins synthesized in the cytosol of the cell must be imported through the inner and outer membranes of chloroplasts in a process requiring energy.
In 2013, researchers from Osaka University led by Masato Nakai discovered and characterized a new transport channel (TIC) in the internal membrane of the chloroplast through which proteins were transported (Science, 339, 571-574). However, the engine for importing proteins across the inner membrane remained a mystery.
Now in The plant cellThis same team collaborated with other Japanese researchers to point to the identification of the elusive protein transport engine essential for chloroplast formation.
"We have identified another new protein complex, twice the mbad of TIC, composed of six related proteins with an accessory protein and functioning as an import engine closely badociated with TIC," says Nakai. "Surprisingly, the six related components all evolved from an enzyme contained in the ancestral cyanobacterial type endosymbiont that degraded unwanted proteins after they were extracted from the membrane."
Although the role of protein degradation has been lost since then, the extraction function has been retained for use as an engine for importation. The team believes that the simultaneous increase in the size of ICT components and the newly identified engine occurred early in the evolution of the green alga, possibly to improve the efficiency of protein imports.
"These results revolutionize the molecular model of chloroplast protein import and help us understand the evolution of chloroplasts from plants and algae," Nakai explains. "This understanding could contribute to biotechnological improvements in the efficiency of crop photosynthesis or the development of plants and algae as factories that manufacture or store proteins in their chloroplasts."
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Material provided by University of Osaka. Note: Content can be changed for style and length.
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