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Genome fusion at stem graft junctions can generate new plant species.

Jyoti Madhusoodanan
Aug 31, 2014

GENOMIC COMBO: The grafted stems of two plant species created Nicotiana tabauca, a new species carrying both parents’ genomes. RALPH BOCK


The paper
I. Fuentes et al., “Horizontal genome transfer as an asexual path to the formation of new species,” Nature, doi:10.1038/nature13291, 2014.

The seed
In nature, plants of different species frequently hybridize sexually to create polyploid offspring, which carry the genomes of both parents. These progeny often have superior traits and can constitute new species. Many modern crops, for instance, are the fruit of such past fusions. Ralph Bock of the Max Planck Institute of Molecular Plant Physiology in Potsdam, Germany, previously found that entire chloroplast genomes could slip from cell to cell across the grafted stem joints of individuals from two different species, leading Bock’s team to test whether nuclear genomes might also migrate and fuse to form polyploid cells in an asexual process.

The graft
Bock and his colleagues tagged tree tobacco (Nicotiana glauca) and cigarette tobacco (Nicotiana tabacum) genomes with genetic markers and grafted their stems together. Cells from the graft junction, when cultured into plantlets, had genomes that were the sum of both parent species and that bore both genetic markers. These plants, dubbed Nicotiana tabauca, were fertile and produced fertile offspring, fulfilling the criteria that qualify it as a new species.    

The fruit
Nuclear genome transfer across grafts might offer a method to create novel crops. One combination Bock is working on is that of tomatoes and chili peppers, “a salsa tomato, if it is successful.”

The field ahead
This is the first study to show “two genomes coming together without meiosis, simply by being adjacent,” says geneticist Annaliese Mason of the University of Queensland in St. Lucia, Australia. Whether this also occurs in the wild is unknown. “If they could take a cutting from a graft and demonstrate that this occurs naturally, that would be fantastic,” says Mason.