What's the News: Scientists have been rooting around in the rice genome
for years, and the same goes for wheat
. But now the long-recalcitrant potato genome has finally been sequenced. Time for a celebration? Perhaps, but biologists can't rest for long: in addition to the just-published genome, there are still three more to sequence in each commercial potato. What's the Context:
The human genome consists of two copies each of 23 chromosomes, one from Mom and one from Dad. And we tend to think of most other species' genomes as roughly comparable. Sure, dogs have 34 pairs and ferrets have 20, but everybody gets two of each chromosome, and each has the same kinds of genes on it, right?
Wrong. Things are a lot weirder in plants, which are known to have bizarre numbers of chromosomes that don't repeat each other much at all. In humans this kind of lackadaisical genetic policing usually means death before an embryo is born. But for some plants, it's normal.
Instead of having two basically similar copies of each of their twelve chromosomes, most potatoes have four wildly varying versions of each. Thus, each set of chromosomes is essentially a separate genome, which makes sequencing difficult, and it's also made breeding potatoes with specific traits a more haphazard process than with plants that just have chromosome pairs.
How the Heck:
To get around the problem of multiple genomes, researchers sought out an unusual South American potato variety that had just two copies of each chromosome.
Then they whittled down the number even further and grew a plant from a pollen cell, which, just like its human analog, a sperm, has one copy of each chromosome. To make the plant viable, they duplicated each of the chromosomes, but for all intents and purposes, the plant had just one set of genes. These could then be easily sequenced using available technology.
Using this sequence, the researchers, who hail from 26 different institutions and banded together specifically for this project, were able to help organize the results of earlier attempts to sequence the genome of a potato similar to those sold in stores. They learned that one reason the potato is so susceptible to blight (like the one that caused the Irish Potato Famine) is that many of the genes involved in disease resistance have been inactivated or destroyed, perhaps the result of years of inbreeding.
The Future Holds: Still, even with this new data, the researchers were only able to make sense of about half the commercial potato's genome. To tackle that challenge, they will need to wait for better technology, which will let them sequence longer sections of DNA---a must-have
for piecing together the arrangement of genes
in an organism with chromosomes as messy as the potato's. And after that? Perhaps we'll finally breed a spud that can stand up to blight. Reference: The Potato Genome Sequencing Consortium. Genome sequence and analysis of the tuber crop potato. Nature, 2011; DOI: 10.1038/nature10158
Image credit: Johannes Jander / flickr