Researchers in France, the United Kingdom and the United States have shed new light on how plants swap genes from plant to plant to help stimulate their evolutionary development. The findings, presented in the journal Current Biology, highlighted that enzymes key to photosynthesis had been shared among plants with only a distant ancestral relationship, and that the metabolic cycle of the recipient plant absorbed the genes, contributing to adaptation. The study was funded in part by a Marie Curie grant under the EU's Seventh Framework Programme (FP7).
Most scientists believe that the passing of genes from parent to offspring, whether it be animals or plants, contributes to their evolution. Genetic modifications are known to emerge throughout this process. But in this latest study, researchers from Brown University in the United States, the Laboratoire Evolution & Diversité Biologique in France, the University of Liverpool and the University of Sheffield in the United Kingdom have identified how genes travel from plant to plant between species with only a distant ancestral kinship.
The researchers observed that a grouping of grasses passed genes many times over millions of years; the genes that were transferred played a crucial role in the plants' photosynthetic machinery. This is especially true in C4 plants, found in hot and tropical climates. These plants also represent 20% of the vegetational covering of our planet.
'As far as we know, this is the first case where nuclear genes that have been transmitted between plants have been incorporated into the primary metabolism and contributed to the evolution of a new trait, in this case C4 photosynthesis,' explained Dr Pascal-Antoine Christin from the Department of Ecology and Evolutionary Biology at Brown University.
The researchers probed the ancestry of two genes encoding enzymes that are integral in C4 photosynthesis: phosphoenolpyruvate carboxylase (ppc) and phosphoenolpyruvate carboxykinase (pck). They also assessed the enzymes' historical presence and function in Alloteropsis, a common and commonly studied grass.
The team first assessed the genes in closely related species, three C4 plants (Alloteropsis angusta, Alloteropsis cimicina and Alloteropsis semialata) and one C3 plant (Alloteropsis eckloniana). They aimed to provide insight on the evolutionary history of the ppc and pck genes, which were found in their C3 common ancestor and were believed to have been adapted in order to stimulate photosynthesis in the offspring C4 plants.
'People were wondering how these genes evolved,' Dr Christin said. 'The global assumption was that an ancestor had the genes, but they weren't involved in photosynthesis, and so were later modified to become C4 photosynthetic agents.'
They evaluated C4 plants whose ppc enzyme was needed for photosynthesis as well as plants whose enzyme was present but that did not impact photosynthesis at all. The researchers hypothesised that the ppc enzymes used in C4 photosynthesis would be closely related to the non-photosynthetic genes from closely related C3 plants, given their common ancestry. But what they found was that the ppc genes involved in C4 photosynthesis were closely related to ppc genes of other C4 species with no close relation in the phylogeny, or family tree. The team also discovered that these plants sharing photosynthetic ppc enzymes had split as many as 20 million years ago. So in spite of the ancestral divergences, the researchers identified an exchange of genes.
'We've long understood how evolutionary adaptations are passed from parents to offspring,' said Dr Colin Osborne of the University of Sheffield, one of the authors of the paper. 'Now we've discovered in plants that they can be passed between distant cousins without direct contact between the species.'
Added Professor Erika Edwards of Brown University: 'What is so exciting here is that these genes are moving from plant to plant in a way we have not seen before. There is no host-parasite relationship between these plants, which is usually when we see this kind of gene movement.'