Plants, grafty little critters…

Plants seem to have hit upon an asexual method that can give rise to new species.
Image: Richard Reames/Wikimedia Commons, www.arborsmith.com.
Image: Richard Reames/Wikimedia Commons, www.arborsmith.com.

When it comes to making new combinations of genes – which may help to generate new species  in the evolutionary process known as speciation – the most usual route in eukaryotes  is via sexual reproduction.  In this ancient process, and speaking rather generally, gametes, made via meiosis (in which the complement of genetic material is reduced), fuse with each other and thereby create a new individual with the full genetic complement of the adult. Generally, this mode of reproduction, whether leading to development of new species or not, is viewed as ‘good’. And sex is favoured during adaptation to new environments. But sex is also ‘expensive’,  and one might expect some organisms to have found a cheaper – better? – way. Although alternatives to sexual reproduction exist – so-called asexual reproduction –  they don’t generate the genetic variety that could give rise to creation [oops, controversial term… – Ed.] of new species.

But, guess what? Plants seem to have hit upon an asexual method that can give rise to new species, as work by Ignacia Fuentes et al., straightforwardly entitled ‘Horizontal genome transfer as an asexual path to the formation of new species’, suggests. Using grafting (a time-honoured, horticultural technique used to join parts from two or more plants so that they appear to grow as a single plant), the team demonstrated that entire nuclear genomes  could be transferred between plant cells of unlike species (and which you wouldn’t expect to be able to be able to reproduce sexually in nature…). Or, in the technical language of a scientific paper, the authors ‘provide direct evidence for this process resulting in speciation by creating a new allopolyploid  plant species from a herbaceous species (Nicotiana tabacum, ‘cigarette tobacco’) and a woody species (N. glauca, ‘tree tobacco’) in the nightshade family (Solanaceae).  The new species is fertile and produces fertile progeny’ (and has even been christened N. tabauca).

All intriguing stuff. And which just goes to demonstrate – again, and if ’twere needed – how much more interesting (better?) plants are than animals! Finally, the authors suggest that this phenomenon could be exploited for the generation of novel allopolyploid crop species. But where will this all end? And isn’t this genetic engineering? Albeit of a kind that occurs naturally? And what should one make of the tree that’s been so multiply and repeatedly grafted that it’s a composite of dozens of different species? Or is it now just one species…? Discuss!

[Ed. – For more on plant grafting, why not check out Charles Melnyk and Elliot Meyerowitz’s ‘primer’ entitled “Plant grafting” in Current Biology 25(5): R184-R188, 2015 [doi:10.1016/j.cub.2015.01.029]? (Which may freely be available from: http://www.cell.com/current-biology/pdf/S0960-9822%2815%2900060-3.pdf). For more on the first author’s grafting ambitions in Arabidopsis and Zea mays, visit http://www.slcu.cam.ac.uk/directory/melnyk-charles, and http://www.slcu.cam.ac.uk/research/meyerowitz-group for ‘Distinguished Associate’ Elliot Meyerowitz]