Literature Review: Kinky Plant Genetics

by Carl Strang

They look so innocent, those plants. Who would suspect that there were kinky goings-on? Well, apparently some scientists have tested such suspicions, and today I report on two studies.

Richard J.A. Buggssend, et al. Rapid, Repeated, and Clustered Loss of Duplicate Genes in Allopolyploid Plant Populations of Independent Origin. Current Biology, 19 January 2012 DOI: 10.1016/j.cub.2011.12.027

As described in a ScienceDaily article. They looked at a hybrid species of goat’s beard which appeared 80 years ago in North America, resulting when complete genomes of separate species combined to produce a polyploid offspring. This appears to be one mechanism by which polyploidy could occur. When compared to a more ancient example of duplicated genomes within this plant group, the authors found similar patterns of gene retention and loss, improving understanding of how the evolutionary process would proceed from the establishment event.

The flower head of our common goat’s beard.

The flower head of our common goat’s beard.

Normally separate species cannot hybridize successfully, and in fact that is an important part of what defines a species. In this case, however, instead of the normal process in which offspring get half the genes of each parent, this new species got all the genes of both parents. Plants, and rarely animals, occasionally double the genetic complement of their offspring in what is essentially an error (the offspring have two copies of each gene). This doesn’t usually lead anywhere in animals, but in plants it has been an important contributor to species diversification, and there have been several episodes of plant species explosions that have followed genome duplications. This apparently is because, with a spare set of genes, there are fewer consequences of mutations and so the stage is set for massive evolutionary experimentation. The usual case is that both parents contributing to the genome duplication belong to the same species, but this goat’s beard provides an example combining the genes of two separate though closely related species.

S. Stegemann, M. Keuthe, S. Greiner, R. Bock. Horizontal transfer of chloroplast genomes between plant species. Proceedings of the National Academy of Sciences, 2012; DOI: 10.1073/pnas.1114076109

From ScienceDaily. They found that horizontal transfer of chloroplasts and their constituent genes can occur when different species grow in physical contact, for instance when trees grow so close together that their trunks fuse. This complicates genetic taxonomy studies.

Two trees side by side, almost with fused trunks. The possibility of gene transferal between them seems merely of academic interest until we look closer and realize that one of these “trees” is poison ivy.

Two trees side by side, almost with fused trunks. The possibility of gene transferal between them seems merely of academic interest until we look closer and realize that one of these “trees” is poison ivy.

Of course, the study found the transfer only in chloroplasts, which don’t carry the genes that make poison ivy a plant of concern to us. Nevertheless, chloroplasts and the similar mitochondria carry their own genes useful in evolutionary genetic studies, so this paper provided a significant cautionary note.

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