By Susan Milius
Plants of different species can swap chloroplasts, the little cellular factories that capture energy from sunlight, when stems graft together. The surprising discovery may explain why evolutionary histories based on chloroplasts sometimes disagree with those based on other sources of DNA.
“If you had asked me before I did this work, I would have said, ‘This isn’t happening,’” says plant geneticist Pal Maliga of Rutgers University in Piscataway, N.J.
Chloroplasts contain their own genetic material, which is typically passed to offspring as mother plants form seed. Now it appears that two plants of different species can exchange chloroplast DNA nonreproductively, by swapping the whole cellular organs through a graft, Maliga’s team and an independent group in Germany report online January 30 in the Proceedings of the National Academy of Sciences.
“It’s genetic engineering done by Mother Nature,” declares geneticist Ralph Bock of the Max Planck Institute for Molecular Plant Physiology in Potsdam-Golm, who led the team in Germany. Plenty of grafts fuse plant to plant in nature, he says, and traveling chloroplasts now offer one explanation for chloroplast-based evolutionary family trees that don’t agree with trees based on DNA from other cell structures.
Chloroplast swapping by grafts may also help researchers engineer better plants, Maliga says. Plants would need to be closely related enough for their tissues to fuse, but grafting could simplify such tasks as introducing specially efficient chloroplasts into lineages of plants, like potatoes, that can lose desirable trait mixes during the genetic shake-up of producing seeds.