Corn: 85% not corn, and missing big pieces
So I’m all excited about the genome festival that I’m seeing, related to the publication of the new sequence version of corn. You can access the main paper in Science, and there’s a very neat diagram in figure 1 that is like looking across time at the sequence data and into the corn nebula. But the thing that cracked me up was this line from the abstract:
Nearly 85% of the genome is composed of hundreds of families of transposable elements, dispersed nonuniformly across the genome.
That means 85% of corn isn’t corn!! And what business do those elements have messing with the genomes?? I am told all the time that messing with plant genomes is wrong and unnatural. Heh.
For full coverage of the big news today I’ll point you to James and the Giant Corn (appropriately enough) who seems to be the CNN (Corn News Network) of 24-hour coverage of many aspects of the work.
I spent my morning looking over the PLoS Maize Special Collection papers, including the intriguing appetizer: 10 Reasons to be Tantalized by the B73 Maize Genome. But I spent longer looking at the CNVs and PAVs paper. I’ve been thinking about CNVs a lot lately, and was interested to see this covered in a non-mammalian species.
Figure 1 is a nice example of how to use VISTA for effective displays in comparative genomics. (If you haven’t used VISTA before you might check out our sponsored free tutorial on that–we are currently working with the VISTA team to update that with their new features too.)
There’s a really striking segment of chromosome 6 that appears to be present in one of the strains they examine and absent in the other (illustrated in figure 4). And it looks like it has genes that are expressed and active in the B73 strain. The ongoing investigation of that is pretty intriguing as well.
The structural variations are not evenly distributed across the genomes. Some places have large occurrences, and some are untouched. It’s clear that just in these two strains there’s a lot more structural diversity than in other species that have been examined:
In the human, rat, dog, mouse, macaque and chimpanzee genomes the average number of CNVs between two individuals is between 15 and 75 –. A high resolution study of eight human genomes  revealed only several hundred insertions and deletions, including CNV and PAV sequences, in the comparison of any two human genomes. In contrast, even after very stringent filtering we identified >3,700 CNV or PAV sequences that represent at least 2,000 events between these two maize genomes.
Emphasis mine. Plants are so much more flexible, apparently….
This is going to lead to some neat clues on heterosis (or hybrid vigor) as the research proceeds with these new tools. What a great time to be a plant scientist. There are some very exciting projects coming along with the tools of genomics.
What I couldn’t locate was any reference to a CNV database (like DGV or CHOP CNV) where you can examine the whole set. I’ll dig through the supplement data to see if I can find out more on that. But I wanted get this post out to celebrate the very nice work and collection of papers on this project. Congrats to the teams involved!
Springer, N., Ying, K., Fu, Y., Ji, T., Yeh, C., Jia, Y., Wu, W., Richmond, T., Kitzman, J., Rosenbaum, H., Iniguez, A., Barbazuk, W., Jeddeloh, J., Nettleton, D., & Schnable, P. (2009). Maize Inbreds Exhibit High Levels of Copy Number Variation (CNV) and Presence/Absence Variation (PAV) in Genome Content PLoS Genetics, 5 (11) DOI: 10.1371/journal.pgen.1000734
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